content: /*
   * 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.content.Context;
  import androidx.annotation.VisibleForTesting;
  import android.util.AttributeSet;
  import android.view.View;
  import android.widget.ScrollView;
  
  /**
   * An extension of ScrollView that will invoke a listener callback when the ScrollView needs
   * scrolling, and when the ScrollView is being scrolled to the bottom. This is often used in Setup
   * Wizard as a way to ensure that users see all the content before proceeding.
   */
  public class BottomScrollView extends ScrollView {
  
    public interface BottomScrollListener {
      void onScrolledToBottom();
  
      void onRequiresScroll();
    }
  
    private BottomScrollListener listener;
    private int scrollThreshold;
    private boolean requiringScroll = false;
  
    private final Runnable checkScrollRunnable =
        new Runnable() {
          @Override
          public void run() {
            checkScroll();
          }
        };
  
    public BottomScrollView(Context context) {
      super(context);
    }
  
    public BottomScrollView(Context context, AttributeSet attrs) {
      super(context, attrs);
    }
  
    public BottomScrollView(Context context, AttributeSet attrs, int defStyle) {
      super(context, attrs, defStyle);
    }
  
    public void setBottomScrollListener(BottomScrollListener l) {
      listener = l;
    }
  
    @VisibleForTesting
    public BottomScrollListener getBottomScrollListener() {
      return listener;
    }
  
    @VisibleForTesting
    public int getScrollThreshold() {
      return scrollThreshold;
    }
  
    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
      super.onLayout(changed, l, t, r, b);
      final View child = getChildAt(0);
      if (child != null) {
        scrollThreshold = Math.max(0, child.getMeasuredHeight() - b + t - getPaddingBottom());
      }
      if (b - t > 0) {
        // Post check scroll in the next run loop, so that the callback methods will be invoked
        // after the layout pass. This way a new layout pass will be scheduled if view
        // properties are changed in the callbacks.
        post(checkScrollRunnable);
      }
    }
  
    @Override
    protected void onScrollChanged(int l, int t, int oldl, int oldt) {
      super.onScrollChanged(l, t, oldl, oldt);
      if (oldt != t) {
        checkScroll();
      }
    }
  
    private void checkScroll() {
      if (listener != null) {
        if (getScrollY() >= scrollThreshold) {
          listener.onScrolledToBottom();
        } else if (!requiringScroll) {
          requiringScroll = true;
          listener.onRequiresScroll();
        }
      }
    }
  }
  