library/main/src/com/android/setupwizardlib/view/FillContentLayout.java

/*
 * Copyright (C) 2017 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 com.android.setupwizardlib.view;

import android.content.Context;
import android.content.res.TypedArray;
import android.util.AttributeSet;
import android.view.View;
import android.widget.FrameLayout;
import com.android.setupwizardlib.R;

/**
 * A layout that will measure its children size based on the space it is given, by using its {@code
 * android:minWidth}, {@code android:minHeight}, {@code android:maxWidth}, and {@code
 * android:maxHeight} values.
 *
 * <p>Typically this is used to show an illustration image or video on the screen. For optimal UX,
 * those assets typically want to occupy the remaining space available on screen within a certain
 * range, and then stop scaling beyond the min/max size attributes. Therefore this view is typically
 * used inside a ScrollView with {@code fillViewport} set to true, together with a linear layout
 * weight or relative layout to fill the remaining space visible on screen.
 *
 * <p>When measuring, this view ignores its children and simply layout according to the minWidth /
 * minHeight given. Therefore it is common for children of this layout to have width / height set to
 * {@code match_parent}. The maxWidth / maxHeight values will then be applied to the children to
 * make sure they are not too big.
 */
public class FillContentLayout extends FrameLayout {

  private int maxWidth;
  private int maxHeight;

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

  public FillContentLayout(Context context, AttributeSet attrs) {
    this(context, attrs, R.attr.suwFillContentLayoutStyle);
  }

  public FillContentLayout(Context context, AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
    init(context, attrs, defStyleAttr);
  }

  private void init(Context context, AttributeSet attrs, int defStyleAttr) {
    TypedArray a =
        context.obtainStyledAttributes(attrs, R.styleable.SuwFillContentLayout, defStyleAttr, 0);

    maxHeight = a.getDimensionPixelSize(R.styleable.SuwFillContentLayout_android_maxHeight, -1);
    maxWidth = a.getDimensionPixelSize(R.styleable.SuwFillContentLayout_android_maxWidth, -1);

    a.recycle();
  }

  @Override
  protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    // Measure this view with the minWidth and minHeight, without asking the children.
    // (Children size is the drawable's intrinsic size, and we don't want that to influence
    // the size of the illustration).
    setMeasuredDimension(
        getDefaultSize(getSuggestedMinimumWidth(), widthMeasureSpec),
        getDefaultSize(getSuggestedMinimumHeight(), heightMeasureSpec));

    int childCount = getChildCount();
    for (int i = 0; i < childCount; i++) {
      measureIllustrationChild(getChildAt(i), getMeasuredWidth(), getMeasuredHeight());
    }
  }

  private void measureIllustrationChild(View child, int parentWidth, int parentHeight) {
    // Modified from ViewGroup#measureChildWithMargins
    final MarginLayoutParams lp = (MarginLayoutParams) child.getLayoutParams();

    // Create measure specs that are no bigger than min(parentSize, maxSize)

    int childWidthMeasureSpec =
        getMaxSizeMeasureSpec(
            Math.min(maxWidth, parentWidth),
            getPaddingLeft() + getPaddingRight() + lp.leftMargin + lp.rightMargin,
            lp.width);
    int childHeightMeasureSpec =
        getMaxSizeMeasureSpec(
            Math.min(maxHeight, parentHeight),
            getPaddingTop() + getPaddingBottom() + lp.topMargin + lp.bottomMargin,
            lp.height);

    child.measure(childWidthMeasureSpec, childHeightMeasureSpec);
  }

  private static int getMaxSizeMeasureSpec(int maxSize, int padding, int childDimension) {
    // Modified from ViewGroup#getChildMeasureSpec
    int size = Math.max(0, maxSize - padding);

    if (childDimension >= 0) {
      // Child wants a specific size... so be it
      return MeasureSpec.makeMeasureSpec(childDimension, MeasureSpec.EXACTLY);
    } else if (childDimension == LayoutParams.MATCH_PARENT) {
      // Child wants to be our size. So be it.
      return MeasureSpec.makeMeasureSpec(size, MeasureSpec.EXACTLY);
    } else if (childDimension == LayoutParams.WRAP_CONTENT) {
      // Child wants to determine its own size. It can't be
      // bigger than us.
      return MeasureSpec.makeMeasureSpec(size, MeasureSpec.AT_MOST);
    }
    return 0;
  }
}