How to use velocitytracker
VelocityTracker usage: 1. Create a java example; 2. Reset the VelocityTracker object in the ACTION_DOWN event and add the touch event to the VelocityTracker; 3. In the ACTION_MOVE event, add the touch event to the VelocityTracker again , and call the `computeCurrentVelocity()` method to calculate the current velocity.
VelocityTracker is a class in the Android framework used to track the velocity of touch events. It can help developers implement complex gesture operations such as sliding, dragging, and quick swiping. This article will introduce the usage of VelocityTracker and how to use it.
First, we need to create a VelocityTracker object. You can obtain a VelocityTracker instance by calling the static method obtain(), as shown below:
java VelocityTracker velocityTracker = VelocityTracker.obtain();
Next, we need to use the VelocityTracker object in the callback method of the touch event to track the speed of the touch event. Usually, we use VelocityTracker in the `onTouchEvent()` method. At the beginning and end of the touch event, we need to call the `addMovement()` method to add the touch event to the VelocityTracker as follows:
java
@Override
public boolean onTouchEvent(MotionEvent event) {
int action = event.getActionMasked();
switch (action) {
case MotionEvent.ACTION_DOWN:
// 触摸事件开始时，重置VelocityTracker
velocityTracker.clear();
velocityTracker.addMovement(event);
break;
case MotionEvent.ACTION_MOVE:
velocityTracker.addMovement(event);
velocityTracker.computeCurrentVelocity(1000); // 计算速度，单位是像素/秒
float xVelocity = velocityTracker.getXVelocity();
float yVelocity = velocityTracker.getYVelocity();
// 使用速度进行相应的操作
break;
case MotionEvent.ACTION_UP:
case MotionEvent.ACTION_CANCEL:
velocityTracker.recycle(); // 释放VelocityTracker对象
break;
}
return true;
}
In the above code, we first repeat the action in the ACTION_DOWN event Set up the VelocityTracker object and add touch events to the VelocityTracker. Then, in the ACTION_MOVE event, we add the touch event to the VelocityTracker again and call the `computeCurrentVelocity()` method to calculate the current velocity. The parameter 1000 here represents the number of pixels per second. Finally, in the ACTION_UP and ACTION_CANCEL events, we need to call the `recycle()` method to release the VelocityTracker object.
Through the above code, we can get the speed in the x-axis and y-axis directions. We can implement some gesture operations based on these speeds, such as sliding, dragging, and quick swiping. For example, we can determine whether the user has performed a fast sliding operation based on the speed, thereby triggering the corresponding animation effect.
To summarize, VelocityTracker is a very useful tool class that can help us track the speed of touch events. By using VelocityTracker, we can implement some complex gesture operations and provide users with a smoother and more natural interactive experience. I hope this article will help you understand the usage of VelocityTracker and how to use it
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