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

/*
 * Copyright (C) 2015 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.annotation.TargetApi;
import android.content.Context;
import android.os.Build;
import android.util.AttributeSet;
import android.view.View;
import android.view.WindowInsets;

/**
 * This class provides sticky header functionality in a scroll view, to use with
 * SetupWizardIllustration. To use this, add a subview tagged with "sticky", or a subview tagged
 * with "stickyContainer" and one of its child tagged as "sticky". The sticky container will be
 * drawn when the sticky element hits the top of the view.
 *
 * <p>There are a few things to note:
 * <ol>
 *   <li>The two supported scenarios are StickyHeaderScrollView -> subview (stickyContainer) ->
 *   sticky, and StickyHeaderScrollView -> container -> subview (sticky).
 *   The arrow (->) represents parent/child relationship and must be immediate child.
 *   <li>If fitsSystemWindows is true, then this will offset the sticking position by the height of
 *   the system decorations at the top of the screen.
 *   <li>For versions before Honeycomb, this will behave like a regular ScrollView.
 * </ol>
 *
 * @see StickyHeaderListView
 */
public class StickyHeaderScrollView extends BottomScrollView {

    private View mSticky;
    private View mStickyContainer;
    private int mStatusBarInset = 0;

    public StickyHeaderScrollView(Context context) {
        super(context);
    }

    public StickyHeaderScrollView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

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

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        super.onLayout(changed, l, t, r, b);
        if (mSticky == null) {
            updateStickyView();
        }
        updateStickyHeaderPosition();
    }

    public void updateStickyView() {
        mSticky = findViewWithTag("sticky");
        mStickyContainer = findViewWithTag("stickyContainer");
    }

    private void updateStickyHeaderPosition() {
        // Note: for pre-Honeycomb the header will not be moved, so this ScrollView essentially
        // behaves like a normal BottomScrollView.
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
            if (mSticky != null) {
                // The view to draw when sticking to the top
                final View drawTarget = mStickyContainer != null ? mStickyContainer : mSticky;
                // The offset to draw the view at when sticky
                final int drawOffset = mStickyContainer != null ? mSticky.getTop() : 0;
                // Position of the draw target, relative to the outside of the scrollView
                final int drawTop = drawTarget.getTop() - getScrollY();
                if (drawTop + drawOffset < mStatusBarInset || !drawTarget.isShown()) {
                    // ScrollView translates the whole canvas so we have to compensate for that
                    drawTarget.setTranslationY(getScrollY() - drawOffset);
                } else {
                    drawTarget.setTranslationY(0);
                }
            }
        }
    }

    @Override
    protected void onScrollChanged(int l, int t, int oldl, int oldt) {
        super.onScrollChanged(l, t, oldl, oldt);
        updateStickyHeaderPosition();
    }

    @Override
    @TargetApi(Build.VERSION_CODES.LOLLIPOP)
    public WindowInsets onApplyWindowInsets(WindowInsets insets) {
        if (getFitsSystemWindows()) {
            mStatusBarInset = insets.getSystemWindowInsetTop();
            insets = insets.replaceSystemWindowInsets(
                    insets.getSystemWindowInsetLeft(),
                    0, /* top */
                    insets.getSystemWindowInsetRight(),
                    insets.getSystemWindowInsetBottom()
            );
        }
        return insets;
    }
}