main/src/com/google/android/setupdesign/view/StickyHeaderListView.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.google.android.setupdesign.view;

import android.annotation.TargetApi;
import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Canvas;
import android.graphics.RectF;
import android.os.Build;
import android.util.AttributeSet;
import android.view.LayoutInflater;
import android.view.MotionEvent;
import android.view.View;
import android.view.WindowInsets;
import android.view.accessibility.AccessibilityEvent;
import android.widget.ListView;
import com.google.android.setupdesign.R;

/**
 * This class provides sticky header functionality in a list view, to use with
 * SetupWizardIllustration. To use this, add a header tagged with "sticky", or a header 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 StickyHeaderListView -> Header (stickyContainer) -> sticky,
 *       and StickyHeaderListView -> Header (sticky). The arrow (->) represents parent/child
 *       relationship and must be immediate child.
 *   <li>The view does not work well with padding. b/16190933
 *   <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.
 * </ol>
 *
 * @see StickyHeaderScrollView
 */
public class StickyHeaderListView extends ListView {

  private View sticky;
  private View stickyContainer;
  private int statusBarInset = 0;
  private final RectF stickyRect = new RectF();

  public StickyHeaderListView(Context context) {
    super(context);
    init(null, android.R.attr.listViewStyle);
  }

  public StickyHeaderListView(Context context, AttributeSet attrs) {
    super(context, attrs);
    init(attrs, android.R.attr.listViewStyle);
  }

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

  private void init(AttributeSet attrs, int defStyleAttr) {
    final TypedArray a =
        getContext()
            .obtainStyledAttributes(attrs, R.styleable.SudStickyHeaderListView, defStyleAttr, 0);
    int headerResId = a.getResourceId(R.styleable.SudStickyHeaderListView_sudHeader, 0);
    if (headerResId != 0) {
      LayoutInflater inflater = LayoutInflater.from(getContext());
      View header = inflater.inflate(headerResId, this, false);
      addHeaderView(header, null, false);
    }
    a.recycle();
  }

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

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

  @Override
  public boolean dispatchTouchEvent(MotionEvent ev) {
    if (stickyRect.contains(ev.getX(), ev.getY())) {
      ev.offsetLocation(-stickyRect.left, -stickyRect.top);
      return stickyContainer.dispatchTouchEvent(ev);
    } else {
      return super.dispatchTouchEvent(ev);
    }
  }

  @Override
  public void draw(Canvas canvas) {
    super.draw(canvas);
    if (sticky != null) {
      final int saveCount = canvas.save();
      // The view to draw when sticking to the top
      final View drawTarget = stickyContainer != null ? stickyContainer : sticky;
      // The offset to draw the view at when sticky
      final int drawOffset = stickyContainer != null ? sticky.getTop() : 0;
      // Position of the draw target, relative to the outside of the scrollView
      final int drawTop = drawTarget.getTop();
      if (drawTop + drawOffset < statusBarInset || !drawTarget.isShown()) {
        // ListView does not translate the canvas, so we can simply draw at the top
        stickyRect.set(
            0,
            -drawOffset + statusBarInset,
            drawTarget.getWidth(),
            drawTarget.getHeight() - drawOffset + statusBarInset);
        canvas.translate(0, stickyRect.top);
        canvas.clipRect(0, 0, drawTarget.getWidth(), drawTarget.getHeight());
        drawTarget.draw(canvas);
      } else {
        stickyRect.setEmpty();
      }
      canvas.restoreToCount(saveCount);
    }
  }

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

  @Override
  public void onInitializeAccessibilityEvent(AccessibilityEvent event) {
    super.onInitializeAccessibilityEvent(event);

    // Decoration-only headers should not count as an item for accessibility, adjust the
    // accessibility event to account for that.
    final int numberOfHeaders = sticky != null ? 1 : 0;
    event.setItemCount(event.getItemCount() - numberOfHeaders);
    event.setFromIndex(Math.max(event.getFromIndex() - numberOfHeaders, 0));
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.ICE_CREAM_SANDWICH) {
      event.setToIndex(Math.max(event.getToIndex() - numberOfHeaders, 0));
    }
  }
}