react-native/ReactAndroid/src/main/java/com/facebook/react/flat/FlatViewGroup.java

/**
 * Copyright (c) 2015-present, Facebook, Inc.
 * All rights reserved.
 *
 * This source code is licensed under the BSD-style license found in the
 * LICENSE file in the root directory of this source tree. An additional grant
 * of patent rights can be found in the PATENTS file in the same directory.
 */

package com.facebook.react.flat;

import java.lang.ref.WeakReference;

import javax.annotation.Nullable;

import android.content.Context;
import android.graphics.Canvas;
import android.view.View;
import android.view.ViewGroup;
import android.view.ViewParent;

import com.facebook.react.uimanager.ReactCompoundView;

/**
 * A view that FlatShadowNode hierarchy maps to. Performs drawing by iterating over
 * array of DrawCommands, executing them one by one.
 */
/* package */ final class FlatViewGroup extends ViewGroup implements ReactCompoundView {
  /**
   * Helper class that allows AttachDetachListener to invalidate the hosting View.
   */
  static final class InvalidateCallback extends WeakReference<FlatViewGroup> {

    private InvalidateCallback(FlatViewGroup view) {
      super(view);
    }

    /**
     * Propagates invalidate() call up to the hosting View (if it's still alive)
     */
    public void invalidate() {
      FlatViewGroup view = get();
      if (view != null) {
        view.invalidate();
      }
    }
  }

  private @Nullable InvalidateCallback mInvalidateCallback;
  private DrawCommand[] mDrawCommands = DrawCommand.EMPTY_ARRAY;
  private AttachDetachListener[] mAttachDetachListeners = AttachDetachListener.EMPTY_ARRAY;
  private NodeRegion[] mNodeRegions = NodeRegion.EMPTY_ARRAY;
  private int mDrawChildIndex = 0;
  private boolean mIsAttached = false;

  /* package */ FlatViewGroup(Context context) {
    super(context);
  }

  @Override
  protected void detachAllViewsFromParent() {
    super.detachAllViewsFromParent();
  }

  @Override
  public int reactTagForTouch(float touchX, float touchY) {
    for (NodeRegion nodeRegion : mNodeRegions) {
      if (nodeRegion.mLeft <= touchX && touchX < nodeRegion.mRight &&
          nodeRegion.mTop <= touchY && touchY < nodeRegion.mBottom) {
        return nodeRegion.mTag;
      }
    }

    // no children found
    return getId();
  }

  @Override
  public void dispatchDraw(Canvas canvas) {
    super.dispatchDraw(canvas);

    for (DrawCommand drawCommand : mDrawCommands) {
      drawCommand.draw(this, canvas);
    }

    if (mDrawChildIndex != getChildCount()) {
      throw new RuntimeException(
          "Did not draw all children: " + mDrawChildIndex + " / " + getChildCount());
    }
    mDrawChildIndex = 0;
  }

  @Override
  protected boolean drawChild(Canvas canvas, View child, long drawingTime) {
    // suppress
    // no drawing -> no invalidate -> return false
    return false;
  }

  @Override
  protected void onLayout(boolean changed, int l, int t, int r, int b) {
    // nothing to do here
  }

  @Override
  protected void onAttachedToWindow() {
    if (mIsAttached) {
      // this is possible, unfortunately.
      return;
    }

    mIsAttached = true;

    super.onAttachedToWindow();
    dispatchOnAttached(mAttachDetachListeners);
  }

  @Override
  protected void onDetachedFromWindow() {
    if (!mIsAttached) {
      throw new RuntimeException("Double detach");
    }

    mIsAttached = false;

    super.onDetachedFromWindow();
    dispatchOnDetached(mAttachDetachListeners);
  }

  /* package */ void drawNextChild(Canvas canvas) {
    View child = getChildAt(mDrawChildIndex);
    super.drawChild(canvas, child, getDrawingTime());

    ++mDrawChildIndex;
  }

  /* package */ void mountDrawCommands(DrawCommand[] drawCommands) {
    mDrawCommands = drawCommands;
    invalidate();
  }

  /* package */ void mountAttachDetachListeners(AttachDetachListener[] listeners) {
    if (mIsAttached) {
      // Ordering of the following 2 statements is very important. While logically it makes sense to
      // detach old listeners first, and only then attach new listeners, this is not very efficient,
      // because a listener can be in both lists. In this case, it will be detached first and then
      // re-attached immediately. This is undesirable for a couple of reasons:
      // 1) performance. Detaching is slow because it may cancel an ongoing network request
      // 2) it may cause flicker: an image that was already loaded may get unloaded.
      //
      // For this reason, we are attaching new listeners first. What this means is that listeners
      // that are in both lists need to gracefully handle a secondary attach and detach events,
      // (i.e. onAttach() being called when already attached, followed by a detach that should be
      // ignored) turning them into no-ops. This will result in no performance loss and no flicker,
      // because ongoing network requests don't get cancelled.
      dispatchOnAttached(listeners);
      dispatchOnDetached(mAttachDetachListeners);
    }
    mAttachDetachListeners = listeners;
  }

  /* package */ void mountNodeRegions(NodeRegion[] nodeRegions) {
    mNodeRegions = nodeRegions;
  }

  /* package */ void mountViews(ViewResolver viewResolver, int[] viewsToAdd, int[] viewsToDetach) {
    for (int viewToAdd : viewsToAdd) {
      if (viewToAdd > 0) {
        View view = ensureViewHasNoParent(viewResolver.getView(viewToAdd));
        addView(view, -1, ensureLayoutParams(view.getLayoutParams()));
      } else {
        View view = ensureViewHasNoParent(viewResolver.getView(-viewToAdd));
        attachViewToParent(view, -1, ensureLayoutParams(view.getLayoutParams()));
      }
    }

    for (int viewToDetach : viewsToDetach) {
      removeDetachedView(viewResolver.getView(viewToDetach), false);
    }
  }

  private View ensureViewHasNoParent(View view) {
    ViewParent oldParent = view.getParent();
    if (oldParent != null) {
      throw new RuntimeException(
          "Cannot add view " + view + " to " + this + " while it has a parent " + oldParent);
    }

    return view;
  }

  private void dispatchOnAttached(AttachDetachListener[] listeners) {
    int numListeners = listeners.length;
    if (numListeners == 0) {
      return;
    }

    InvalidateCallback callback = getInvalidateCallback();
    for (AttachDetachListener listener : listeners) {
      listener.onAttached(callback);
    }
  }

  private InvalidateCallback getInvalidateCallback() {
    if (mInvalidateCallback == null) {
      mInvalidateCallback = new InvalidateCallback(this);
    }
    return mInvalidateCallback;
  }

  private static void dispatchOnDetached(AttachDetachListener[] listeners) {
    for (AttachDetachListener listener : listeners) {
      listener.onDetached();
    }
  }

  private ViewGroup.LayoutParams ensureLayoutParams(ViewGroup.LayoutParams lp) {
    if (checkLayoutParams(lp)) {
      return lp;
    }
    return generateDefaultLayoutParams();
  }
}