core-ui/java/android/support/v4/view/PagerTitleStrip.java - platform/frameworks/support - Git at Google

 /*
  * Copyright (C) 2011 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 package android.support.v4.view;

 import android.content.Context;
 import android.content.res.TypedArray;
 import android.database.DataSetObserver;
 import android.graphics.drawable.Drawable;
 import android.support.annotation.ColorInt;
 import android.support.annotation.FloatRange;
 import android.support.v4.widget.TextViewCompat;
 import android.text.TextUtils.TruncateAt;
 import android.util.AttributeSet;
 import android.util.TypedValue;
 import android.view.Gravity;
 import android.view.ViewGroup;
 import android.view.ViewParent;
 import android.widget.TextView;

 import java.lang.ref.WeakReference;

 /**
  * PagerTitleStrip is a non-interactive indicator of the current, next,
  * and previous pages of a {@link ViewPager}. It is intended to be used as a
  * child view of a ViewPager widget in your XML layout.
  * Add it as a child of a ViewPager in your layout file and set its
  * android:layout_gravity to TOP or BOTTOM to pin it to the top or bottom
  * of the ViewPager. The title from each page is supplied by the method
  * {@link PagerAdapter#getPageTitle(int)} in the adapter supplied to
  * the ViewPager.
  *
  * <p>For an interactive indicator, see {@link PagerTabStrip}.</p>
  */
 @ViewPager.DecorView
 public class PagerTitleStrip extends ViewGroup {
     private static final String TAG = "PagerTitleStrip";

     ViewPager mPager;
     TextView mPrevText;
     TextView mCurrText;
     TextView mNextText;

     private int mLastKnownCurrentPage = -1;
     float mLastKnownPositionOffset = -1;
     private int mScaledTextSpacing;
     private int mGravity;

     private boolean mUpdatingText;
     private boolean mUpdatingPositions;

     private final PageListener mPageListener = new PageListener();

     private WeakReference<PagerAdapter> mWatchingAdapter;

     private static final int[] ATTRS = new int[] {
         android.R.attr.textAppearance,
         android.R.attr.textSize,
         android.R.attr.textColor,
         android.R.attr.gravity
     };

     private static final int[] TEXT_ATTRS = new int[] {
         0x0101038c // android.R.attr.textAllCaps
     };

     private static final float SIDE_ALPHA = 0.6f;
     private static final int TEXT_SPACING = 16; // dip

     private int mNonPrimaryAlpha;
     int mTextColor;

     interface PagerTitleStripImpl {
         void setSingleLineAllCaps(TextView text);
     }

     static class PagerTitleStripImplBase implements PagerTitleStripImpl {
         @Override
         public void setSingleLineAllCaps(TextView text) {
             text.setSingleLine();
         }
     }

     static class PagerTitleStripImplIcs implements PagerTitleStripImpl {
         @Override
         public void setSingleLineAllCaps(TextView text) {
             PagerTitleStripIcs.setSingleLineAllCaps(text);
         }
     }

     private static final PagerTitleStripImpl IMPL;
     static {
         if (android.os.Build.VERSION.SDK_INT >= 14) {
             IMPL = new PagerTitleStripImplIcs();
         } else {
             IMPL = new PagerTitleStripImplBase();
         }
     }

     private static void setSingleLineAllCaps(TextView text) {
         IMPL.setSingleLineAllCaps(text);
     }

     public PagerTitleStrip(Context context) {
         this(context, null);
     }

     public PagerTitleStrip(Context context, AttributeSet attrs) {
         super(context, attrs);

         addView(mPrevText = new TextView(context));
         addView(mCurrText = new TextView(context));
         addView(mNextText = new TextView(context));

         final TypedArray a = context.obtainStyledAttributes(attrs, ATTRS);
         final int textAppearance = a.getResourceId(0, 0);
         if (textAppearance != 0) {
             TextViewCompat.setTextAppearance(mPrevText, textAppearance);
             TextViewCompat.setTextAppearance(mCurrText, textAppearance);
             TextViewCompat.setTextAppearance(mNextText, textAppearance);
         }
         final int textSize = a.getDimensionPixelSize(1, 0);
         if (textSize != 0) {
             setTextSize(TypedValue.COMPLEX_UNIT_PX, textSize);
         }
         if (a.hasValue(2)) {
             final int textColor = a.getColor(2, 0);
             mPrevText.setTextColor(textColor);
             mCurrText.setTextColor(textColor);
             mNextText.setTextColor(textColor);
         }
         mGravity = a.getInteger(3, Gravity.BOTTOM);
         a.recycle();

         mTextColor = mCurrText.getTextColors().getDefaultColor();
         setNonPrimaryAlpha(SIDE_ALPHA);

         mPrevText.setEllipsize(TruncateAt.END);
         mCurrText.setEllipsize(TruncateAt.END);
         mNextText.setEllipsize(TruncateAt.END);

         boolean allCaps = false;
         if (textAppearance != 0) {
             final TypedArray ta = context.obtainStyledAttributes(textAppearance, TEXT_ATTRS);
             allCaps = ta.getBoolean(0, false);
             ta.recycle();
         }

         if (allCaps) {
             setSingleLineAllCaps(mPrevText);
             setSingleLineAllCaps(mCurrText);
             setSingleLineAllCaps(mNextText);
         } else {
             mPrevText.setSingleLine();
             mCurrText.setSingleLine();
             mNextText.setSingleLine();
         }

         final float density = context.getResources().getDisplayMetrics().density;
         mScaledTextSpacing = (int) (TEXT_SPACING * density);
     }

     /**
      * Set the required spacing between title segments.
      *
      * @param spacingPixels Spacing between each title displayed in pixels
      */
     public void setTextSpacing(int spacingPixels) {
         mScaledTextSpacing = spacingPixels;
         requestLayout();
     }

     /**
      * @return The required spacing between title segments in pixels
      */
     public int getTextSpacing() {
         return mScaledTextSpacing;
     }

     /**
      * Set the alpha value used for non-primary page titles.
      *
      * @param alpha Opacity value in the range 0-1f
      */
     public void setNonPrimaryAlpha(@FloatRange(from = 0.0, to = 1.0) float alpha) {
         mNonPrimaryAlpha = (int) (alpha * 255) & 0xFF;
         final int transparentColor = (mNonPrimaryAlpha << 24) | (mTextColor & 0xFFFFFF);
         mPrevText.setTextColor(transparentColor);
         mNextText.setTextColor(transparentColor);
     }

     /**
      * Set the color value used as the base color for all displayed page titles.
      * Alpha will be ignored for non-primary page titles. See {@link #setNonPrimaryAlpha(float)}.
      *
      * @param color Color hex code in 0xAARRGGBB format
      */
     public void setTextColor(@ColorInt int color) {
         mTextColor = color;
         mCurrText.setTextColor(color);
         final int transparentColor = (mNonPrimaryAlpha << 24) | (mTextColor & 0xFFFFFF);
         mPrevText.setTextColor(transparentColor);
         mNextText.setTextColor(transparentColor);
     }

     /**
      * Set the default text size to a given unit and value.
      * See {@link TypedValue} for the possible dimension units.
      *
      * <p>Example: to set the text size to 14px, use
      * setTextSize(TypedValue.COMPLEX_UNIT_PX, 14);</p>
      *
      * @param unit The desired dimension unit
      * @param size The desired size in the given units
      */
     public void setTextSize(int unit, float size) {
         mPrevText.setTextSize(unit, size);
         mCurrText.setTextSize(unit, size);
         mNextText.setTextSize(unit, size);
     }

     /**
      * Set the {@link Gravity} used to position text within the title strip.
      * Only the vertical gravity component is used.
      *
      * @param gravity {@link Gravity} constant for positioning title text
      */
     public void setGravity(int gravity) {
         mGravity = gravity;
         requestLayout();
     }

     @Override
     protected void onAttachedToWindow() {
         super.onAttachedToWindow();

         final ViewParent parent = getParent();
         if (!(parent instanceof ViewPager)) {
             throw new IllegalStateException(
                     "PagerTitleStrip must be a direct child of a ViewPager.");
         }

         final ViewPager pager = (ViewPager) parent;
         final PagerAdapter adapter = pager.getAdapter();

         pager.setInternalPageChangeListener(mPageListener);
         pager.addOnAdapterChangeListener(mPageListener);
         mPager = pager;
         updateAdapter(mWatchingAdapter != null ? mWatchingAdapter.get() : null, adapter);
     }

     @Override
     protected void onDetachedFromWindow() {
         super.onDetachedFromWindow();
         if (mPager != null) {
             updateAdapter(mPager.getAdapter(), null);
             mPager.setInternalPageChangeListener(null);
             mPager.removeOnAdapterChangeListener(mPageListener);
             mPager = null;
         }
     }

     void updateText(int currentItem, PagerAdapter adapter) {
         final int itemCount = adapter != null ? adapter.getCount() : 0;
         mUpdatingText = true;

         CharSequence text = null;
         if (currentItem >= 1 && adapter != null) {
             text = adapter.getPageTitle(currentItem - 1);
         }
         mPrevText.setText(text);

         mCurrText.setText(adapter != null && currentItem < itemCount
                 ? adapter.getPageTitle(currentItem) : null);

         text = null;
         if (currentItem + 1 < itemCount && adapter != null) {
             text = adapter.getPageTitle(currentItem + 1);
         }
         mNextText.setText(text);

         // Measure everything
         final int width = getWidth() - getPaddingLeft() - getPaddingRight();
         final int maxWidth = Math.max(0, (int) (width * 0.8f));
         final int childWidthSpec = MeasureSpec.makeMeasureSpec(maxWidth, MeasureSpec.AT_MOST);
         final int childHeight = getHeight() - getPaddingTop() - getPaddingBottom();
         final int maxHeight = Math.max(0, childHeight);
         final int childHeightSpec = MeasureSpec.makeMeasureSpec(maxHeight, MeasureSpec.AT_MOST);
         mPrevText.measure(childWidthSpec, childHeightSpec);
         mCurrText.measure(childWidthSpec, childHeightSpec);
         mNextText.measure(childWidthSpec, childHeightSpec);

         mLastKnownCurrentPage = currentItem;

         if (!mUpdatingPositions) {
             updateTextPositions(currentItem, mLastKnownPositionOffset, false);
         }

         mUpdatingText = false;
     }

     @Override
     public void requestLayout() {
         if (!mUpdatingText) {
             super.requestLayout();
         }
     }

     void updateAdapter(PagerAdapter oldAdapter, PagerAdapter newAdapter) {
         if (oldAdapter != null) {
             oldAdapter.unregisterDataSetObserver(mPageListener);
             mWatchingAdapter = null;
         }
         if (newAdapter != null) {
             newAdapter.registerDataSetObserver(mPageListener);
             mWatchingAdapter = new WeakReference<PagerAdapter>(newAdapter);
         }
         if (mPager != null) {
             mLastKnownCurrentPage = -1;
             mLastKnownPositionOffset = -1;
             updateText(mPager.getCurrentItem(), newAdapter);
             requestLayout();
         }
     }

     void updateTextPositions(int position, float positionOffset, boolean force) {
         if (position != mLastKnownCurrentPage) {
             updateText(position, mPager.getAdapter());
         } else if (!force && positionOffset == mLastKnownPositionOffset) {
             return;
         }

         mUpdatingPositions = true;

         final int prevWidth = mPrevText.getMeasuredWidth();
         final int currWidth = mCurrText.getMeasuredWidth();
         final int nextWidth = mNextText.getMeasuredWidth();
         final int halfCurrWidth = currWidth / 2;

         final int stripWidth = getWidth();
         final int stripHeight = getHeight();
         final int paddingLeft = getPaddingLeft();
         final int paddingRight = getPaddingRight();
         final int paddingTop = getPaddingTop();
         final int paddingBottom = getPaddingBottom();
         final int textPaddedLeft = paddingLeft + halfCurrWidth;
         final int textPaddedRight = paddingRight + halfCurrWidth;
         final int contentWidth = stripWidth - textPaddedLeft - textPaddedRight;

         float currOffset = positionOffset + 0.5f;
         if (currOffset > 1.f) {
             currOffset -= 1.f;
         }
         final int currCenter = stripWidth - textPaddedRight - (int) (contentWidth * currOffset);
         final int currLeft = currCenter - currWidth / 2;
         final int currRight = currLeft + currWidth;

         final int prevBaseline = mPrevText.getBaseline();
         final int currBaseline = mCurrText.getBaseline();
         final int nextBaseline = mNextText.getBaseline();
         final int maxBaseline = Math.max(Math.max(prevBaseline, currBaseline), nextBaseline);
         final int prevTopOffset = maxBaseline - prevBaseline;
         final int currTopOffset = maxBaseline - currBaseline;
         final int nextTopOffset = maxBaseline - nextBaseline;
         final int alignedPrevHeight = prevTopOffset + mPrevText.getMeasuredHeight();
         final int alignedCurrHeight = currTopOffset + mCurrText.getMeasuredHeight();
         final int alignedNextHeight = nextTopOffset + mNextText.getMeasuredHeight();
         final int maxTextHeight = Math.max(Math.max(alignedPrevHeight, alignedCurrHeight),
                 alignedNextHeight);

         final int vgrav = mGravity & Gravity.VERTICAL_GRAVITY_MASK;

         int prevTop;
         int currTop;
         int nextTop;
         switch (vgrav) {
             default:
             case Gravity.TOP:
                 prevTop = paddingTop + prevTopOffset;
                 currTop = paddingTop + currTopOffset;
                 nextTop = paddingTop + nextTopOffset;
                 break;
             case Gravity.CENTER_VERTICAL:
                 final int paddedHeight = stripHeight - paddingTop - paddingBottom;
                 final int centeredTop = (paddedHeight - maxTextHeight) / 2;
                 prevTop = centeredTop + prevTopOffset;
                 currTop = centeredTop + currTopOffset;
                 nextTop = centeredTop + nextTopOffset;
                 break;
             case Gravity.BOTTOM:
                 final int bottomGravTop = stripHeight - paddingBottom - maxTextHeight;
                 prevTop = bottomGravTop + prevTopOffset;
                 currTop = bottomGravTop + currTopOffset;
                 nextTop = bottomGravTop + nextTopOffset;
                 break;
         }

         mCurrText.layout(currLeft, currTop, currRight,
                 currTop + mCurrText.getMeasuredHeight());

         final int prevLeft = Math.min(paddingLeft, currLeft - mScaledTextSpacing - prevWidth);
         mPrevText.layout(prevLeft, prevTop, prevLeft + prevWidth,
                 prevTop + mPrevText.getMeasuredHeight());

         final int nextLeft = Math.max(stripWidth - paddingRight - nextWidth,
                 currRight + mScaledTextSpacing);
         mNextText.layout(nextLeft, nextTop, nextLeft + nextWidth,
                 nextTop + mNextText.getMeasuredHeight());

         mLastKnownPositionOffset = positionOffset;
         mUpdatingPositions = false;
     }

     @Override
     protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
         final int widthMode = MeasureSpec.getMode(widthMeasureSpec);
         if (widthMode != MeasureSpec.EXACTLY) {
             throw new IllegalStateException("Must measure with an exact width");
         }

         final int heightPadding = getPaddingTop() + getPaddingBottom();
         final int childHeightSpec = getChildMeasureSpec(heightMeasureSpec,
                 heightPadding, LayoutParams.WRAP_CONTENT);

         final int widthSize = MeasureSpec.getSize(widthMeasureSpec);
         final int widthPadding = (int) (widthSize * 0.2f);
         final int childWidthSpec = getChildMeasureSpec(widthMeasureSpec,
                 widthPadding, LayoutParams.WRAP_CONTENT);

         mPrevText.measure(childWidthSpec, childHeightSpec);
         mCurrText.measure(childWidthSpec, childHeightSpec);
         mNextText.measure(childWidthSpec, childHeightSpec);

         final int height;
         final int heightMode = MeasureSpec.getMode(heightMeasureSpec);
         if (heightMode == MeasureSpec.EXACTLY) {
             height = MeasureSpec.getSize(heightMeasureSpec);
         } else {
             final int textHeight = mCurrText.getMeasuredHeight();
             final int minHeight = getMinHeight();
             height = Math.max(minHeight, textHeight + heightPadding);
         }

         final int childState = ViewCompat.getMeasuredState(mCurrText);
         final int measuredHeight = ViewCompat.resolveSizeAndState(height, heightMeasureSpec,
                 childState << ViewCompat.MEASURED_HEIGHT_STATE_SHIFT);
         setMeasuredDimension(widthSize, measuredHeight);
     }

     @Override
     protected void onLayout(boolean changed, int l, int t, int r, int b) {
         if (mPager != null) {
             final float offset = mLastKnownPositionOffset >= 0 ? mLastKnownPositionOffset : 0;
             updateTextPositions(mLastKnownCurrentPage, offset, true);
         }
     }

     int getMinHeight() {
         int minHeight = 0;
         final Drawable bg = getBackground();
         if (bg != null) {
             minHeight = bg.getIntrinsicHeight();
         }
         return minHeight;
     }

     private class PageListener extends DataSetObserver implements ViewPager.OnPageChangeListener,
             ViewPager.OnAdapterChangeListener {
         private int mScrollState;

         PageListener() {
         }

         @Override
         public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
             if (positionOffset > 0.5f) {
                 // Consider ourselves to be on the next page when we're 50% of the way there.
                 position++;
             }
             updateTextPositions(position, positionOffset, false);
         }

         @Override
         public void onPageSelected(int position) {
             if (mScrollState == ViewPager.SCROLL_STATE_IDLE) {
                 // Only update the text here if we're not dragging or settling.
                 updateText(mPager.getCurrentItem(), mPager.getAdapter());

                 final float offset = mLastKnownPositionOffset >= 0 ? mLastKnownPositionOffset : 0;
                 updateTextPositions(mPager.getCurrentItem(), offset, true);
             }
         }

         @Override
         public void onPageScrollStateChanged(int state) {
             mScrollState = state;
         }

         @Override
         public void onAdapterChanged(ViewPager viewPager, PagerAdapter oldAdapter,
                 PagerAdapter newAdapter) {
             updateAdapter(oldAdapter, newAdapter);
         }

         @Override
         public void onChanged() {
             updateText(mPager.getCurrentItem(), mPager.getAdapter());

             final float offset = mLastKnownPositionOffset >= 0 ? mLastKnownPositionOffset : 0;
             updateTextPositions(mPager.getCurrentItem(), offset, true);
         }
     }
 }
	/*
	* Copyright (C) 2011 The Android Open Source Project
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	package android.support.v4.view;

	import android.content.Context;
	import android.content.res.TypedArray;
	import android.database.DataSetObserver;
	import android.graphics.drawable.Drawable;
	import android.support.annotation.ColorInt;
	import android.support.annotation.FloatRange;
	import android.support.v4.widget.TextViewCompat;
	import android.text.TextUtils.TruncateAt;
	import android.util.AttributeSet;
	import android.util.TypedValue;
	import android.view.Gravity;
	import android.view.ViewGroup;
	import android.view.ViewParent;
	import android.widget.TextView;

	import java.lang.ref.WeakReference;

	/**
	* PagerTitleStrip is a non-interactive indicator of the current, next,
	* and previous pages of a {@link ViewPager}. It is intended to be used as a
	* child view of a ViewPager widget in your XML layout.
	* Add it as a child of a ViewPager in your layout file and set its
	* android:layout_gravity to TOP or BOTTOM to pin it to the top or bottom
	* of the ViewPager. The title from each page is supplied by the method
	* {@link PagerAdapter#getPageTitle(int)} in the adapter supplied to
	* the ViewPager.
	*
	* <p>For an interactive indicator, see {@link PagerTabStrip}.</p>
	*/
	@ViewPager.DecorView
	public class PagerTitleStrip extends ViewGroup {
	private static final String TAG = "PagerTitleStrip";

	ViewPager mPager;
	TextView mPrevText;
	TextView mCurrText;
	TextView mNextText;

	private int mLastKnownCurrentPage = -1;
	float mLastKnownPositionOffset = -1;
	private int mScaledTextSpacing;
	private int mGravity;

	private boolean mUpdatingText;
	private boolean mUpdatingPositions;

	private final PageListener mPageListener = new PageListener();

	private WeakReference<PagerAdapter> mWatchingAdapter;

	private static final int[] ATTRS = new int[] {
	android.R.attr.textAppearance,
	android.R.attr.textSize,
	android.R.attr.textColor,
	android.R.attr.gravity
	};

	private static final int[] TEXT_ATTRS = new int[] {
	0x0101038c // android.R.attr.textAllCaps
	};

	private static final float SIDE_ALPHA = 0.6f;
	private static final int TEXT_SPACING = 16; // dip

	private int mNonPrimaryAlpha;
	int mTextColor;

	interface PagerTitleStripImpl {
	void setSingleLineAllCaps(TextView text);
	}

	static class PagerTitleStripImplBase implements PagerTitleStripImpl {
	@Override
	public void setSingleLineAllCaps(TextView text) {
	text.setSingleLine();
	}
	}

	static class PagerTitleStripImplIcs implements PagerTitleStripImpl {
	@Override
	public void setSingleLineAllCaps(TextView text) {
	PagerTitleStripIcs.setSingleLineAllCaps(text);
	}
	}

	private static final PagerTitleStripImpl IMPL;
	static {
	if (android.os.Build.VERSION.SDK_INT >= 14) {
	IMPL = new PagerTitleStripImplIcs();
	} else {
	IMPL = new PagerTitleStripImplBase();
	}
	}

	private static void setSingleLineAllCaps(TextView text) {
	IMPL.setSingleLineAllCaps(text);
	}

	public PagerTitleStrip(Context context) {
	this(context, null);
	}

	public PagerTitleStrip(Context context, AttributeSet attrs) {
	super(context, attrs);

	addView(mPrevText = new TextView(context));
	addView(mCurrText = new TextView(context));
	addView(mNextText = new TextView(context));

	final TypedArray a = context.obtainStyledAttributes(attrs, ATTRS);
	final int textAppearance = a.getResourceId(0, 0);
	if (textAppearance != 0) {
	TextViewCompat.setTextAppearance(mPrevText, textAppearance);
	TextViewCompat.setTextAppearance(mCurrText, textAppearance);
	TextViewCompat.setTextAppearance(mNextText, textAppearance);
	}
	final int textSize = a.getDimensionPixelSize(1, 0);
	if (textSize != 0) {
	setTextSize(TypedValue.COMPLEX_UNIT_PX, textSize);
	}
	if (a.hasValue(2)) {
	final int textColor = a.getColor(2, 0);
	mPrevText.setTextColor(textColor);
	mCurrText.setTextColor(textColor);
	mNextText.setTextColor(textColor);
	}
	mGravity = a.getInteger(3, Gravity.BOTTOM);
	a.recycle();

	mTextColor = mCurrText.getTextColors().getDefaultColor();
	setNonPrimaryAlpha(SIDE_ALPHA);

	mPrevText.setEllipsize(TruncateAt.END);
	mCurrText.setEllipsize(TruncateAt.END);
	mNextText.setEllipsize(TruncateAt.END);

	boolean allCaps = false;
	if (textAppearance != 0) {
	final TypedArray ta = context.obtainStyledAttributes(textAppearance, TEXT_ATTRS);
	allCaps = ta.getBoolean(0, false);
	ta.recycle();
	}

	if (allCaps) {
	setSingleLineAllCaps(mPrevText);
	setSingleLineAllCaps(mCurrText);
	setSingleLineAllCaps(mNextText);
	} else {
	mPrevText.setSingleLine();
	mCurrText.setSingleLine();
	mNextText.setSingleLine();
	}

	final float density = context.getResources().getDisplayMetrics().density;
	mScaledTextSpacing = (int) (TEXT_SPACING * density);
	}

	/**
	* Set the required spacing between title segments.
	*
	* @param spacingPixels Spacing between each title displayed in pixels
	*/
	public void setTextSpacing(int spacingPixels) {
	mScaledTextSpacing = spacingPixels;
	requestLayout();
	}

	/**
	* @return The required spacing between title segments in pixels
	*/
	public int getTextSpacing() {
	return mScaledTextSpacing;
	}

	/**
	* Set the alpha value used for non-primary page titles.
	*
	* @param alpha Opacity value in the range 0-1f
	*/
	public void setNonPrimaryAlpha(@FloatRange(from = 0.0, to = 1.0) float alpha) {
	mNonPrimaryAlpha = (int) (alpha * 255) & 0xFF;
	final int transparentColor = (mNonPrimaryAlpha << 24) \| (mTextColor & 0xFFFFFF);
	mPrevText.setTextColor(transparentColor);
	mNextText.setTextColor(transparentColor);
	}

	/**
	* Set the color value used as the base color for all displayed page titles.
	* Alpha will be ignored for non-primary page titles. See {@link #setNonPrimaryAlpha(float)}.
	*
	* @param color Color hex code in 0xAARRGGBB format
	*/
	public void setTextColor(@ColorInt int color) {
	mTextColor = color;
	mCurrText.setTextColor(color);
	final int transparentColor = (mNonPrimaryAlpha << 24) \| (mTextColor & 0xFFFFFF);
	mPrevText.setTextColor(transparentColor);
	mNextText.setTextColor(transparentColor);
	}

	/**
	* Set the default text size to a given unit and value.
	* See {@link TypedValue} for the possible dimension units.
	*
	* <p>Example: to set the text size to 14px, use
	* setTextSize(TypedValue.COMPLEX_UNIT_PX, 14);</p>
	*
	* @param unit The desired dimension unit
	* @param size The desired size in the given units
	*/
	public void setTextSize(int unit, float size) {
	mPrevText.setTextSize(unit, size);
	mCurrText.setTextSize(unit, size);
	mNextText.setTextSize(unit, size);
	}

	/**
	* Set the {@link Gravity} used to position text within the title strip.
	* Only the vertical gravity component is used.
	*
	* @param gravity {@link Gravity} constant for positioning title text
	*/
	public void setGravity(int gravity) {
	mGravity = gravity;
	requestLayout();
	}

	@Override
	protected void onAttachedToWindow() {
	super.onAttachedToWindow();

	final ViewParent parent = getParent();
	if (!(parent instanceof ViewPager)) {
	throw new IllegalStateException(
	"PagerTitleStrip must be a direct child of a ViewPager.");
	}

	final ViewPager pager = (ViewPager) parent;
	final PagerAdapter adapter = pager.getAdapter();

	pager.setInternalPageChangeListener(mPageListener);
	pager.addOnAdapterChangeListener(mPageListener);
	mPager = pager;
	updateAdapter(mWatchingAdapter != null ? mWatchingAdapter.get() : null, adapter);
	}

	@Override
	protected void onDetachedFromWindow() {
	super.onDetachedFromWindow();
	if (mPager != null) {
	updateAdapter(mPager.getAdapter(), null);
	mPager.setInternalPageChangeListener(null);
	mPager.removeOnAdapterChangeListener(mPageListener);
	mPager = null;
	}
	}

	void updateText(int currentItem, PagerAdapter adapter) {
	final int itemCount = adapter != null ? adapter.getCount() : 0;
	mUpdatingText = true;

	CharSequence text = null;
	if (currentItem >= 1 && adapter != null) {
	text = adapter.getPageTitle(currentItem - 1);
	}
	mPrevText.setText(text);

	mCurrText.setText(adapter != null && currentItem < itemCount
	? adapter.getPageTitle(currentItem) : null);

	text = null;
	if (currentItem + 1 < itemCount && adapter != null) {
	text = adapter.getPageTitle(currentItem + 1);
	}
	mNextText.setText(text);

	// Measure everything
	final int width = getWidth() - getPaddingLeft() - getPaddingRight();
	final int maxWidth = Math.max(0, (int) (width * 0.8f));
	final int childWidthSpec = MeasureSpec.makeMeasureSpec(maxWidth, MeasureSpec.AT_MOST);
	final int childHeight = getHeight() - getPaddingTop() - getPaddingBottom();
	final int maxHeight = Math.max(0, childHeight);
	final int childHeightSpec = MeasureSpec.makeMeasureSpec(maxHeight, MeasureSpec.AT_MOST);
	mPrevText.measure(childWidthSpec, childHeightSpec);
	mCurrText.measure(childWidthSpec, childHeightSpec);
	mNextText.measure(childWidthSpec, childHeightSpec);

	mLastKnownCurrentPage = currentItem;

	if (!mUpdatingPositions) {
	updateTextPositions(currentItem, mLastKnownPositionOffset, false);
	}

	mUpdatingText = false;
	}

	@Override
	public void requestLayout() {
	if (!mUpdatingText) {
	super.requestLayout();
	}
	}

	void updateAdapter(PagerAdapter oldAdapter, PagerAdapter newAdapter) {
	if (oldAdapter != null) {
	oldAdapter.unregisterDataSetObserver(mPageListener);
	mWatchingAdapter = null;
	}
	if (newAdapter != null) {
	newAdapter.registerDataSetObserver(mPageListener);
	mWatchingAdapter = new WeakReference<PagerAdapter>(newAdapter);
	}
	if (mPager != null) {
	mLastKnownCurrentPage = -1;
	mLastKnownPositionOffset = -1;
	updateText(mPager.getCurrentItem(), newAdapter);
	requestLayout();
	}
	}

	void updateTextPositions(int position, float positionOffset, boolean force) {
	if (position != mLastKnownCurrentPage) {
	updateText(position, mPager.getAdapter());
	} else if (!force && positionOffset == mLastKnownPositionOffset) {
	return;
	}

	mUpdatingPositions = true;

	final int prevWidth = mPrevText.getMeasuredWidth();
	final int currWidth = mCurrText.getMeasuredWidth();
	final int nextWidth = mNextText.getMeasuredWidth();
	final int halfCurrWidth = currWidth / 2;

	final int stripWidth = getWidth();
	final int stripHeight = getHeight();
	final int paddingLeft = getPaddingLeft();
	final int paddingRight = getPaddingRight();
	final int paddingTop = getPaddingTop();
	final int paddingBottom = getPaddingBottom();
	final int textPaddedLeft = paddingLeft + halfCurrWidth;
	final int textPaddedRight = paddingRight + halfCurrWidth;
	final int contentWidth = stripWidth - textPaddedLeft - textPaddedRight;

	float currOffset = positionOffset + 0.5f;
	if (currOffset > 1.f) {
	currOffset -= 1.f;
	}
	final int currCenter = stripWidth - textPaddedRight - (int) (contentWidth * currOffset);
	final int currLeft = currCenter - currWidth / 2;
	final int currRight = currLeft + currWidth;

	final int prevBaseline = mPrevText.getBaseline();
	final int currBaseline = mCurrText.getBaseline();
	final int nextBaseline = mNextText.getBaseline();
	final int maxBaseline = Math.max(Math.max(prevBaseline, currBaseline), nextBaseline);
	final int prevTopOffset = maxBaseline - prevBaseline;
	final int currTopOffset = maxBaseline - currBaseline;
	final int nextTopOffset = maxBaseline - nextBaseline;
	final int alignedPrevHeight = prevTopOffset + mPrevText.getMeasuredHeight();
	final int alignedCurrHeight = currTopOffset + mCurrText.getMeasuredHeight();
	final int alignedNextHeight = nextTopOffset + mNextText.getMeasuredHeight();
	final int maxTextHeight = Math.max(Math.max(alignedPrevHeight, alignedCurrHeight),
	alignedNextHeight);

	final int vgrav = mGravity & Gravity.VERTICAL_GRAVITY_MASK;

	int prevTop;
	int currTop;
	int nextTop;
	switch (vgrav) {
	default:
	case Gravity.TOP:
	prevTop = paddingTop + prevTopOffset;
	currTop = paddingTop + currTopOffset;
	nextTop = paddingTop + nextTopOffset;
	break;
	case Gravity.CENTER_VERTICAL:
	final int paddedHeight = stripHeight - paddingTop - paddingBottom;
	final int centeredTop = (paddedHeight - maxTextHeight) / 2;
	prevTop = centeredTop + prevTopOffset;
	currTop = centeredTop + currTopOffset;
	nextTop = centeredTop + nextTopOffset;
	break;
	case Gravity.BOTTOM:
	final int bottomGravTop = stripHeight - paddingBottom - maxTextHeight;
	prevTop = bottomGravTop + prevTopOffset;
	currTop = bottomGravTop + currTopOffset;
	nextTop = bottomGravTop + nextTopOffset;
	break;
	}

	mCurrText.layout(currLeft, currTop, currRight,
	currTop + mCurrText.getMeasuredHeight());

	final int prevLeft = Math.min(paddingLeft, currLeft - mScaledTextSpacing - prevWidth);
	mPrevText.layout(prevLeft, prevTop, prevLeft + prevWidth,
	prevTop + mPrevText.getMeasuredHeight());

	final int nextLeft = Math.max(stripWidth - paddingRight - nextWidth,
	currRight + mScaledTextSpacing);
	mNextText.layout(nextLeft, nextTop, nextLeft + nextWidth,
	nextTop + mNextText.getMeasuredHeight());

	mLastKnownPositionOffset = positionOffset;
	mUpdatingPositions = false;
	}

	@Override
	protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
	final int widthMode = MeasureSpec.getMode(widthMeasureSpec);
	if (widthMode != MeasureSpec.EXACTLY) {
	throw new IllegalStateException("Must measure with an exact width");
	}

	final int heightPadding = getPaddingTop() + getPaddingBottom();
	final int childHeightSpec = getChildMeasureSpec(heightMeasureSpec,
	heightPadding, LayoutParams.WRAP_CONTENT);

	final int widthSize = MeasureSpec.getSize(widthMeasureSpec);
	final int widthPadding = (int) (widthSize * 0.2f);
	final int childWidthSpec = getChildMeasureSpec(widthMeasureSpec,
	widthPadding, LayoutParams.WRAP_CONTENT);

	mPrevText.measure(childWidthSpec, childHeightSpec);
	mCurrText.measure(childWidthSpec, childHeightSpec);
	mNextText.measure(childWidthSpec, childHeightSpec);

	final int height;
	final int heightMode = MeasureSpec.getMode(heightMeasureSpec);
	if (heightMode == MeasureSpec.EXACTLY) {
	height = MeasureSpec.getSize(heightMeasureSpec);
	} else {
	final int textHeight = mCurrText.getMeasuredHeight();
	final int minHeight = getMinHeight();
	height = Math.max(minHeight, textHeight + heightPadding);
	}

	final int childState = ViewCompat.getMeasuredState(mCurrText);
	final int measuredHeight = ViewCompat.resolveSizeAndState(height, heightMeasureSpec,
	childState << ViewCompat.MEASURED_HEIGHT_STATE_SHIFT);
	setMeasuredDimension(widthSize, measuredHeight);
	}

	@Override
	protected void onLayout(boolean changed, int l, int t, int r, int b) {
	if (mPager != null) {
	final float offset = mLastKnownPositionOffset >= 0 ? mLastKnownPositionOffset : 0;
	updateTextPositions(mLastKnownCurrentPage, offset, true);
	}
	}

	int getMinHeight() {
	int minHeight = 0;
	final Drawable bg = getBackground();
	if (bg != null) {
	minHeight = bg.getIntrinsicHeight();
	}
	return minHeight;
	}

	private class PageListener extends DataSetObserver implements ViewPager.OnPageChangeListener,
	ViewPager.OnAdapterChangeListener {
	private int mScrollState;

	PageListener() {
	}

	@Override
	public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
	if (positionOffset > 0.5f) {
	// Consider ourselves to be on the next page when we're 50% of the way there.
	position++;
	}
	updateTextPositions(position, positionOffset, false);
	}

	@Override
	public void onPageSelected(int position) {
	if (mScrollState == ViewPager.SCROLL_STATE_IDLE) {
	// Only update the text here if we're not dragging or settling.
	updateText(mPager.getCurrentItem(), mPager.getAdapter());

	final float offset = mLastKnownPositionOffset >= 0 ? mLastKnownPositionOffset : 0;
	updateTextPositions(mPager.getCurrentItem(), offset, true);
	}
	}

	@Override
	public void onPageScrollStateChanged(int state) {
	mScrollState = state;
	}

	@Override
	public void onAdapterChanged(ViewPager viewPager, PagerAdapter oldAdapter,
	PagerAdapter newAdapter) {
	updateAdapter(oldAdapter, newAdapter);
	}

	@Override
	public void onChanged() {
	updateText(mPager.getCurrentItem(), mPager.getAdapter());

	final float offset = mLastKnownPositionOffset >= 0 ? mLastKnownPositionOffset : 0;
	updateTextPositions(mPager.getCurrentItem(), offset, true);
	}
	}
	}