Android onTouch() 方法不起作用（滑动检测）

Question

我正在使用 Android Studio 2.3.2 在 Android 上对 Snake 进行编程

为了移动蛇，我制作了一个 onTouchListener 来检测用户是否在滑动以及朝哪个方向（北、南、东、西）滑动

下面是View.onTouchListener的onTouch方法：

@Override
public boolean onTouch(View v, MotionEvent event) {
    switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN:
            prevX = event.getX();
            prevY = event.getY();

            break;
        case MotionEvent.ACTION_UP:
            float newX = event.getX();
            float newY = event.getY();


            //Calculates where we swiped

            if (Math.abs(newX - prevX) > Math.abs(newY - prevY)) {
                //LEFT - RiGHT Direction

                if( newX > prevX) {
                    //RIGHT
                    gameEngine.updateDirection(Direction.East);
                } else {
                    //LEFT
                    gameEngine.updateDirection(Direction.West);
                }
            } else {
                // UP-DOWN Direction
                if (newY > prevY) {
                    //DOWN
                    gameEngine.updateDirection(Direction.South);
                } else {
                    //UP
                    gameEngine.updateDirection(Direction.North);
                }
            }

            break;
    }
    return false;
}

问题在于它只检测 LEFT 和 RIGHT（即 EAST 和 WEST）。 而且我不知道为什么没有检测到 UP 和 DOWN。

Answer 1

试试下面的代码。它对我有用。

Java：

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;

public class MainSnake extends AppCompatActivity implements View.OnTouchListener {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main_snake);
        findViewById(R.id.main_view).setOnTouchListener(this);
    }


    float prevX, prevY;
    @Override
    public boolean onTouch(View v, MotionEvent event) {
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                prevX = event.getX();
                prevY = event.getY();

                return true;
            case MotionEvent.ACTION_UP:
                float newX = event.getX();
                float newY = event.getY();


                //Calculates where we swiped

                if (Math.abs(newX - prevX) > Math.abs(newY - prevY)) {
                    //LEFT - RiGHT Direction

                    if( newX > prevX) {
                        //RIGHT
                        Log.i("TOUCH INFO", "Right");
                    } else {
                        //LEFT
                        Log.i("TOUCH INFO", "Left");
                    }
                } else {
                    // UP-DOWN Direction
                    if (newY > prevY) {
                        //DOWN
                        Log.i("TOUCH INFO", "Down");
                    } else {
                        //UP
                        Log.i("TOUCH INFO", "Up");
                    }
                }

                break;
        }
        return false;
    }
}

XML：

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/main_view">

</android.support.constraint.ConstraintLayout>

Answer 2

您必须在 ACTION_DOWN 之后返回“True”。这告诉 Android 监视 ACTION_UP 事件。

switch (event.getAction()) {
    case MotionEvent.ACTION_DOWN:
        prevX = event.getX();
        prevY = event.getY();

        return true;