安卓自定义 View 启航

<?xml version="1.0" encoding="utf-8"?>
<resources>

    <attr name="titleText" format="string" />
    <attr name="titleTextColor" format="color" />
    <attr name="titleTextSize" format="dimension" />

    <declare-styleable name="CustomTitleView">
        <attr name="titleText" />
        <attr name="titleTextColor" />
        <attr name="titleTextSize" />
    </declare-styleable>

</resources>

mVelocityTracker = VelocityTracker.obtain();
mVelocityTracker.addMovement(MotionEvent event);

// 获取1000毫秒内运行的像素
mVelocityTracker.computeCurrentVeleocity(1000)

// 获取1S内 X 方向上移动的像素
mVelocityTracker.getXVelocity()

// 最后记得释放
mVelocityTracker.recycle()

ViewDragHelper mViewDragHelper = ViewDragHelper.create(context, 1.0f, new ViewDragHelper.Callback(){
    clampViewPositionHorizontal(View child, int left, int dx)
    clampViewPositionVertical(View child, int left, int dx)
    onViewDragStateChanged(int state){
      ViewDragHelper.STATE_DRAGGING:
      ViewDragHelper.STATE_IDLE:
      ViewDragHelper.STATE_SETTLING:
    }
}

然后代理两个方法

```java
public boolean onINterrceptTouchEvent(MotionEvent ev) {
  return mViewDragHelper.shouldInterceptTouchEvent(ev);
}

public boolean onTouchEvent(MotionEvent ev) {
  mViewDragHelper.processTouchEvent(ev);
  return true;
}

int specMode = MeasureSpec.getMode(measureSpec);
int specSize = MeasureSpec.getSize(measureSpec);

int measureSpec = MeasureSpec.makeMeasureSpec(size, mode);