View的几个高度/宽度

自定义view的过程

onMeasure()–>onLayout()–>onDraw()

• onMeasure() 计算当前各个子view的高宽度

• onLayout() 确定各个子view在父容器的位置

  需要4个参数确定子view的位置。都是相对父容器的
  left 左边距离
  top 上边距离
  right 右边距离
  bottom 下边距离
  如果我想让某个子view占据父布局的上一半。就是 child.layout(0,0,0,1/2*父容器的高度)

• onDraw() 开始绘制 真正开始具体绘制

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1 view.getLayoutParams().height/width

获取当前view在父容器中的布局宽高度, 父容器根据LayoutParams()可以确定这个view的怎么布局。这里的height 和 width 可以是具体的数，也可以是如下的参数。每个不一样的ViewGroup拥有不一样的LayoutParams。LayoutParams()不仅仅是确定高度和宽度，还可以确定Margin，gravity。

获取来源：1.动态布局，可以任何时候手动setLayoutParams，setLayoutParams方法里面会触发requestLayout();requestLayout触发父容器重新依次计算子view在父布局的位置。
2.android.view.ViewGroup 的绘制过程中的方法会自动调用 view.setLayoutParams(params);注意可能获取为null，还没没有添加到布局中，自然不存在 LayoutParams。在方法 public void addView(**)会创建params = generateDefaultLayoutParams();每一种不同的布局类型，不同的generateDefaultLayoutParams初始化策略。

获取时机：addView之后

public static class LayoutParams {
       /**
        * Special value for the height or width requested by a View.
        * FILL_PARENT means that the view wants to be as big as its parent,
        * minus the parent's padding, if any. This value is deprecated
        * starting in API Level 8 and replaced by {@link #MATCH_PARENT}.
        */
       @SuppressWarnings({"UnusedDeclaration"})
       @Deprecated
       public static final int FILL_PARENT = -1;

       /**
        * Special value for the height or width requested by a View.
        * MATCH_PARENT means that the view wants to be as big as its parent,
        * minus the parent's padding, if any. Introduced in API Level 8.
        */
       public static final int MATCH_PARENT = -1;

       /**
        * Special value for the height or width requested by a View.
        * WRAP_CONTENT means that the view wants to be just large enough to fit
        * its own internal content, taking its own padding into account.
        */
       public static final int WRAP_CONTENT = -2;

       /**
        * Information about how wide the view wants to be. Can be one of the
        * constants FILL_PARENT (replaced by MATCH_PARENT
        * in API Level 8) or WRAP_CONTENT, or an exact size.
        */
       @ViewDebug.ExportedProperty(category = "layout", mapping = {
           @ViewDebug.IntToString(from = MATCH_PARENT, to = "MATCH_PARENT"),
           @ViewDebug.IntToString(from = WRAP_CONTENT, to = "WRAP_CONTENT")
       })
       public int width;

       /**
        * Information about how tall the view wants to be. Can be one of the
        * constants FILL_PARENT (replaced by MATCH_PARENT
        * in API Level 8) or WRAP_CONTENT, or an exact size.
        */
       @ViewDebug.ExportedProperty(category = "layout", mapping = {
           @ViewDebug.IntToString(from = MATCH_PARENT, to = "MATCH_PARENT"),
           @ViewDebug.IntToString(from = WRAP_CONTENT, to = "WRAP_CONTENT")
       })
       public int height;

       ...
}

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2 view().getHeight()/getWidth()

获取当前view的高度和宽度，需在onLayout之后获取，就是用laout中的 宽度就是=左边-去右边 高度 = 上边-下边

获取时机：必须在onLayout 之后

public final int getHeight() {
        return mBottom - mTop;
    }

     public final int getWidth() {
        return mRight - mLeft;
    }

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3 view().getMeasuredHeight()/getMeasuredWidth()

获取view自己的原始高度,

  //The raw measured width of this view.
  public final int getMeasuredWidth() {
        //取mod  MEASURED_SIZE_MASK = 0x00ffffff;
        return mMeasuredWidth & MEASURED_SIZE_MASK;
    }
    //The raw measured height of this view.
    public final int getMeasuredHeight() {
    return mMeasuredHeight & MEASURED_SIZE_MASK;
}

值的来源 onMeasure中调用的setMeasuredDimensionRaw

private void setMeasuredDimensionRaw(int measuredWidth, int measuredHeight) {
       mMeasuredWidth = measuredWidth;
       mMeasuredHeight = measuredHeight;

       mPrivateFlags |= PFLAG_MEASURED_DIMENSION_SET;
   }

setMeasuredDimensionRaw来源于view#measure(int widthMeasureSpec, int heightMeasureSpec)
widthMeasureSpec 和 heightMeasureSpec 和 view 和 原始layoutpram 又相关。

获取时机：必须在view的onMeasure之后

关于MeasuredHeight() 请参考 MeasureSpec

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4. 出发点的BUG 为什么view重叠的时候，有时可以点击？而有时不可以点击？

如图所示，存在以为视图布局如下,当以你以为的布局进行点击的时候，发现点击小view时而可以，时而不行？why？本质是点击事件的分发有关，点击事件由ViewGroup发往子View的时候，是从后面向前遍历的。也就是说，当2个view重叠的情况，谁在后面，谁响应本次事件。

可见android.view.ViewGroup#dispatchTouchEvent

public boolean dispatchTouchEvent(MotionEvent ev){
   ---
   if (newTouchTarget == null && childrenCount != 0) {
    final float x = ev.getX(actionIndex);
    final float y = ev.getY(actionIndex);
    // Find a child that can receive the event.
    // Scan children from front to back.
    // 从后向前遍历 一个可以接受点击事件的 view
    final ArrayList<View> preorderedList = buildTouchDispatchChildList();
    final boolean customOrder = preorderedList == null
            && isChildrenDrawingOrderEnabled();
    final View[] children = mChildren;
    for (int i = childrenCount - 1; i >= 0; i--) {
        final int childIndex = getAndVerifyPreorderedIndex(
                childrenCount, i, customOrder);
        final View child = getAndVerifyPreorderedView(
                preorderedList, children, childIndex);
        if (childWithAccessibilityFocus != null) {
            if (childWithAccessibilityFocus != child) {
                continue;
            }
            childWithAccessibilityFocus = null;
            i = childrenCount - 1;
        }

        //判断子 view 能不能收到 点击事件，和点击事件是不是在 子view的范围中
        if (!canViewReceivePointerEvents(child)
                || !isTransformedTouchPointInView(x, y, child, null)) {
            ev.setTargetAccessibilityFocus(false);
            continue;
        }

        if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) 
   ---
}

最后才在 dispatchTransformedTouchEvent 调用 child.dispatchTouchEvent(event)

在onMeasure 调用 super.onMeasure 在super.onMeasure中计算子view的高度的时候会用到子view原来的LayoutParams，然后再计算 set子view的LayoutParams的，最后在onLayout的时候 通过 getMeasuredWidth()获取高度。问题在于getMeasuredWidth()获取的高度是在super.onMeasure的时候就已经确定了的，并不是在在onMeasure计算的高度，实际在于刚才set的LayoutParams。后面进入的时候 LayoutParams已经被更新了，再次super.onMeasure 更新的MeasuredWidth()就是和新的LayoutParams相关了,展示就会正确。

问题就是第一次进来的时候就会获取错误的高度，onlayout并不是我们手动计算的高度。