Android 系统源码分析——Launcher3自定义控件之Workspace

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https://rainmonth.github.io/posts/A180705.html

Android Launcher3分析——自定义控件之Workspace

绘制方面

可以参考文章Android View的绘制流程分析

onMeasure

Workspace 并没有进行什么测量工作，测量工作都交给其父类PagedView处理，看看PagedView的onMeasure如何处理的。

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protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
  // 没有子View直接调用View的onMeasure方法，退出
  if (getChildCount() == 0) {
    super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    return;
  }

  // We measure the dimensions of the PagedView to be larger than the pages so that when we
  // zoom out (and scale down), the view is still contained in the parent
  int widthMode = MeasureSpec.getMode(widthMeasureSpec);
  int widthSize = MeasureSpec.getSize(widthMeasureSpec);
  int heightMode = MeasureSpec.getMode(heightMeasureSpec);
  int heightSize = MeasureSpec.getSize(heightMeasureSpec);
  // NOTE: We multiply by 2f to account for the fact that depending on the offset of the
  // viewport, we can be at most one and a half screens offset once we scale down
  DisplayMetrics dm = getResources().getDisplayMetrics();
  int maxSize = Math.max(dm.widthPixels + mInsets.left + mInsets.right,
                         dm.heightPixels + mInsets.top + mInsets.bottom);

  int parentWidthSize = (int) (2f * maxSize);
  int parentHeightSize = (int) (2f * maxSize);
  int scaledWidthSize, scaledHeightSize;
  if (mUseMinScale) {
    scaledWidthSize = (int) (parentWidthSize / mMinScale);
    scaledHeightSize = (int) (parentHeightSize / mMinScale);
  } else {
    scaledWidthSize = widthSize;
    scaledHeightSize = heightSize;
  }
  mViewport.set(0, 0, widthSize, heightSize);

  if (widthMode == MeasureSpec.UNSPECIFIED || heightMode == MeasureSpec.UNSPECIFIED) {
    super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    return;
  }

  // Return early if we aren't given a proper dimension
  if (widthSize <= 0 || heightSize <= 0) {
    super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    return;
  }

  /* Allow the height to be set as WRAP_CONTENT. This allows the particular case
   * of the All apps view on XLarge displays to not take up more space then it needs. Width
   * is still not allowed to be set as WRAP_CONTENT since many parts of the code expect
   * each page to have the same width.
   */
  final int verticalPadding = getPaddingTop() + getPaddingBottom();
  final int horizontalPadding = getPaddingLeft() + getPaddingRight();

  int referenceChildWidth = 0;
  // The children are given the same width and height as the workspace
  // unless they were set to WRAP_CONTENT
  if (DEBUG) Log.d(TAG, "PagedView.onMeasure(): " + widthSize + ", " + heightSize);
  if (DEBUG) Log.d(TAG, "PagedView.scaledSize: " + scaledWidthSize + ", " + scaledHeightSize);
  if (DEBUG) Log.d(TAG, "PagedView.parentSize: " + parentWidthSize + ", " + parentHeightSize);
  if (DEBUG) Log.d(TAG, "PagedView.horizontalPadding: " + horizontalPadding);
  if (DEBUG) Log.d(TAG, "PagedView.verticalPadding: " + verticalPadding);
  final int childCount = getChildCount();
  // 遍历子View（只处理可见的子View）
  for (int i = 0; i < childCount; i++) {
    // disallowing padding in paged view (just pass 0)
    final View child = getPageAt(i);
    // 处理可见子View
    if (child.getVisibility() != GONE) {
      // 获取子布局的布局参数
      final LayoutParams lp = (LayoutParams) child.getLayoutParams();

      int childWidthMode;// 子View的宽度测量规范
      int childHeightMode;// 子View的高度测量规范
      int childWidth;// 子View的宽
      int childHeight;// 子View的高

      // 根据布局参数来设置子View的宽、高以及宽高规范
      if (!lp.isFullScreenPage) {
        if (lp.width == LayoutParams.WRAP_CONTENT) {
          childWidthMode = MeasureSpec.AT_MOST;
        } else {
          childWidthMode = MeasureSpec.EXACTLY;
        }

        if (lp.height == LayoutParams.WRAP_CONTENT) {
          childHeightMode = MeasureSpec.AT_MOST;
        } else {
          childHeightMode = MeasureSpec.EXACTLY;
        }

        childWidth = getViewportWidth() - horizontalPadding
          - mInsets.left - mInsets.right;
        childHeight = getViewportHeight() - verticalPadding
          - mInsets.top - mInsets.bottom;
        mNormalChildHeight = childHeight;
      } else {
        childWidthMode = MeasureSpec.EXACTLY;
        childHeightMode = MeasureSpec.EXACTLY;

        childWidth = getViewportWidth() - mInsets.left - mInsets.right;
        childHeight = getViewportHeight();
      }
      if (referenceChildWidth == 0) {
        referenceChildWidth = childWidth;
      }

      // 获取子View的宽高测量规范
      final int childWidthMeasureSpec =
        MeasureSpec.makeMeasureSpec(childWidth, childWidthMode);
      final int childHeightMeasureSpec =
        MeasureSpec.makeMeasureSpec(childHeight, childHeightMode);
      // 根据获取到的测量规范测量每个子View
      child.measure(childWidthMeasureSpec, childHeightMeasureSpec);
    }
  }
  setMeasuredDimension(scaledWidthSize, scaledHeightSize);
}

onLayout

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@Override
protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
  if (mFirstLayout && mCurrentPage >= 0 && mCurrentPage < getChildCount()) {
    mWallpaperOffset.syncWithScroll();
    mWallpaperOffset.jumpToFinal();
  }
  super.onLayout(changed, left, top, right, bottom);
}

主要还是调用PagedView的onLayout方法，只是在调用之前根据是否第一次Layout及当前页是否在有效范围来对Launcher壁纸的偏移量做处理。

onDraw

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@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);

// Call back to LauncherModel to finish binding after the first draw
post(mBindPages);
}

调用PagedView的onDraw方法，然后告知通知LauncherModel绑定完成。

注意：ViewGroup作为一个View的容器，为了性能上的考虑，通常是不需要调用自己的onDraw函数的（不需要重写），只有在我们设置了ViewGroup的背景或者调用setWillNotDraw(false)时才会调用。

事件处理方面

可以参考文章Android View的事件处理流程分析

onInterceptTouchEvent(MotionEvent ev)

onTouchEvent(MotionEvent ev)