android - 在 Android 中获取 onTouch ACTION_MOVE 事件的速度

Question

这应该是一件非常简单的事情。用户将手指放在屏幕上并在屏幕上拖动。 onTouch 触发了两个事件:

• MotionEvent.ACTION_DOWN
• MotionEvent.ACTION_MOVE

现在，我如何计算 ACTION_MOVE 手势的速度？用户在手势过程中手指拖得更慢或更快，所以我想我需要计算两个中间触摸点之间的速度:lastTouchedPointX,lastTouchedPointY 和 event.getX(),event.getY()。

以前有人做过吗？

Answer 1

您所需要的可以通过使用标准 VelocityTracker 来实现类(class)。更多关于谷歌用户输入最佳实践的详细信息，同时跟踪移动here .下面的大部分代码(通过在 X 和 Y 轴上显示每个抛掷/移动的速度来演示 VelocityTracker 的使用)取自之前的资源链接:

import android.os.Bundle;
import android.app.Activity;
import android.support.v4.view.VelocityTrackerCompat;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.widget.TextView;

public class MainActivity extends Activity {

    private VelocityTracker mVelocityTracker = null;
    private TextView mTextView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mTextView = new TextView(this);
        mTextView.setText("Move finger on screen to get velocity.");
        setContentView(mTextView);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        int index = event.getActionIndex();
        int action = event.getActionMasked();
        int pointerId = event.getPointerId(index);

        switch (action) {
        case MotionEvent.ACTION_DOWN:
            if (mVelocityTracker == null) {

                // Retrieve a new VelocityTracker object to watch the velocity
                // of a motion.
                mVelocityTracker = VelocityTracker.obtain();
            } else {

                // Reset the velocity tracker back to its initial state.
                mVelocityTracker.clear();
            }

            // Add a user's movement to the tracker.
            mVelocityTracker.addMovement(event);
            break;
        case MotionEvent.ACTION_MOVE:
            mVelocityTracker.addMovement(event);
            // When you want to determine the velocity, call
            // computeCurrentVelocity(). Then call getXVelocity()
            // and getYVelocity() to retrieve the velocity for each pointer ID.
            mVelocityTracker.computeCurrentVelocity(1000);

            // Log velocity of pixels per second
            // Best practice to use VelocityTrackerCompat where possible.
            mTextView.setText("X velocity: "
                    + VelocityTrackerCompat.getXVelocity(mVelocityTracker,
                            pointerId)
                    + "\nY velocity: "
                    + VelocityTrackerCompat.getYVelocity(mVelocityTracker,
                            pointerId));
            break;
        case MotionEvent.ACTION_UP:
            break;
        case MotionEvent.ACTION_CANCEL:
            // Return a VelocityTracker object back to be re-used by others.
            mVelocityTracker.recycle();
            break;
        }
        return true;
    }

}