View工作原理一：坐标系

1.android坐标系

屏幕的左上角顶点作为坐标系原点，向左，向下为正方向。

Android坐标系

View.getLocationInWindow(int[] location)一个控件在其父窗口中的坐标位置

//View#getLocationInWindow
   public void getLocationInWindow(int[] location) {  
        if (location == null || location.length < 2) {  
            throw new IllegalArgumentException("location must be an array of two integers");  
        }  
        if (mAttachInfo == null) {  
            // When the view is not attached to a window, this method does not make sense  
            location[0] = location[1] = 0;  
            return;  
        }  
        float[] position = mAttachInfo.mTmpTransformLocation;  
        position[0] = position[1] = 0.0f;  
        if (!hasIdentityMatrix()) {  
            getMatrix().mapPoints(position);  
        }  
        position[0] += mLeft;  
        position[1] += mTop;  
        ViewParent viewParent = mParent;  
        while (viewParent instanceof View) {  
            final View view = (View) viewParent;  
            position[0] -= view.mScrollX;  
            position[1] -= view.mScrollY;  
            if (!view.hasIdentityMatrix()) {  
                view.getMatrix().mapPoints(position);  
            }  
            position[0] += view.mLeft;  
            position[1] += view.mTop;  
            viewParent = view.mParent;  
         }  
        if (viewParent instanceof ViewRootImpl) {  
            // *cough*  
            final ViewRootImpl vr = (ViewRootImpl) viewParent;  
            position[1] -= vr.mCurScrollY;  
        }  
        location[0] = (int) (position[0] + 0.5f);  
        location[1] = (int) (position[1] + 0.5f);  
    }  

View.getLocationOnScreen(int[] location) 一个控件在其整个屏幕上的坐标位置

//View#getLocationOnScreen
 public void getLocationOnScreen(int[] location) {
    getLocationInWindow(location);
    final AttachInfo info = mAttachInfo;
    if (info != null) {
      location[0] += info.mWindowLeft;
      location[1] += info.mWindowTop;
    }
  }

2.View坐标系

View坐标系与Android 坐标系并不冲突。

View自身坐标

View提供的API
•getTop()：获取View顶边到其父布局顶边的距离
•getLeft()：获取View左边到其父布局左边的距离
•getRight()：获取View右边到其父布局左边的距离
•getBottom()：获取View底边到其父布局顶边的距离

根据上图得到的数据，我们可以计算出View的宽高。View源码中getHeight()和getWidth()也是使用相同方法实现的，如下：

    @ViewDebug.ExportedProperty(category = "layout")
    public final int getWidth() {
        return mRight - mLeft;
    }
    @ViewDebug.ExportedProperty(category = "layout")
    public final int getHeight() {
        return mBottom - mTop;
    }

假设圆点是我们的触摸点，它会激活相应的触摸事件

触摸后的坐标

• getX()：获取点击位置离View左边的距离
• getY()：获取点击位置离View顶边的距离
• getRawX()：获取点击位置离屏幕左边的距离
• getRawY()：获取点击位置离屏幕顶边的距离