How to Use VelocityTracker in Android Basic Knowledge

VelocityTracker is a tool class in Android used to track the speed of touch events. It can be used to calculate the speed of touch events within a specified time interval, as well as the speed between two touch events.

The basic steps for using VelocityTracker are as follows:

1. Initialize a VelocityTracker object, which can be created within the onCreate() method of an Activity.

VelocityTracker velocityTracker = VelocityTracker.obtain();

1. Use VelocityTracker to track the velocity in the handling of touch events.

@Override
public boolean onTouchEvent(MotionEvent event) {
    // 将触摸事件传递给VelocityTracker
    velocityTracker.addMovement(event);
    // 处理触摸事件
    // ...
    return true;
}

1. Call the computeCurrentVelocity() method of VelocityTracker to calculate the speed at places where speed calculation is needed, such as when a touch event ends.

@Override
public boolean onTouchEvent(MotionEvent event) {
    // 处理触摸事件
    // ...
    if (event.getAction() == MotionEvent.ACTION_UP) {
        // 计算速度
        velocityTracker.computeCurrentVelocity(1000); // 1000表示时间间隔，单位为毫秒
        // 获取X轴和Y轴方向上的速度
        float xVelocity = velocityTracker.getXVelocity();
        float yVelocity = velocityTracker.getYVelocity();
        // 处理速度
        // ...
    }
    return true;
}

1. VelocityTracker objects need to be recycled when no longer in use.

@Override
protected void onDestroy() {
    super.onDestroy();
    // 回收VelocityTracker对象
    velocityTracker.recycle();
}

Important points to note:

1. When using VelocityTracker, it is important to ensure that there is only one VelocityTracker object in each touch event sequence.
2. Before calculating the speed, it is necessary to call the computeCurrentVelocity() method, which will calculate the speed within the specified time interval.
3. If you are no longer using the VelocityTracker object, you need to call the recycle() method to recycle it for future reuse.