java - 获取触摸输入的 x 和 y 坐标(Android studio，Java)

Question

我想获取触摸输入的 x 和 y 坐标。我正在尝试使用:

package com.example.benjamin.labb3;

import android.app.Activity;
import android.content.Context;
import android.content.res.AssetManager;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Point;
import android.os.Bundle;
import android.view.Display;
import android.view.MotionEvent;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.view.View;
import android.view.Window;
import java.io.IOException;
import java.io.InputStream;
import java.util.Random;

import android.view.View.OnTouchListener;

    public class Main extends Activity implements OnTouchListener {

    DrawView drawView;
    String inputAction = "";
    Point touch;

    @Override public void onCreate(Bundle savedInstanceState){
        super.onCreate(savedInstanceState);
        requestWindowFeature(Window.FEATURE_NO_TITLE);

        drawView = new DrawView(this);
        setContentView(drawView);
        drawView.setOnTouchListener(this);
    }

    @Override public void onResume(){
        super.onResume();
        drawView.resume();
    }

    @Override public void onPause(){
        super.onPause();
        drawView.pause();
    }

    public boolean onTouch (View v, MotionEvent event) {
        touch.x = (int)event.getX();
        touch.y= (int)event.getY();
        return true;
    }

    public class  DrawView extends SurfaceView implements Runnable {
        Thread gameloop = null;
        SurfaceHolder surface;
        volatile boolean running = false;
        AssetManager assets = null;
        BitmapFactory.Options options = null;
        Bitmap incect[];
        int frame = 0;

        public DrawView(Context context){
            super(context);
            surface = getHolder();
            assets = context.getAssets();
            options = new BitmapFactory.Options();
            options.inPreferredConfig = Bitmap.Config.ARGB_8888;

            incect = new Bitmap[2];

            try {
                for (int n = 0; n < 2; n++){
                    String fileName = "incect"+Integer.toString(n+1)+".png";
                    InputStream istream = assets.open(fileName);
                    incect[n] = BitmapFactory.decodeStream(istream,null,options);
                    istream.close();
                }
            } catch (IOException e){
                e.printStackTrace();
            }
        }

        public void resume() {
            running = true;
            gameloop = new Thread(this);
            gameloop.start();
        }

        public void pause() {
            running = false;
            boolean retry = true;
            while (retry) {
                try {
                    gameloop.join();
                    retry = false;
                } catch (InterruptedException e){}
            }
        }

        @Override public void run(){

            Point size = new Point();
            Display display = getWindowManager().getDefaultDisplay();
            display.getSize(size);
            Random wR = new Random();
            Random hR = new Random();
            int width = size.x;
            int height = size.y;
            int randomW = wR.nextInt(width-20)+20;
            int randomH = hR.nextInt(height-20)+20;

            while (running){

                if(!surface.getSurface().isValid())
                    continue;

                Canvas canvas = surface.lockCanvas();
                canvas.drawColor(Color.rgb(85,107,47));
                canvas.drawBitmap(incect[frame],randomW-10,randomH-10,null);
                surface.unlockCanvasAndPost(canvas);
                frame ++;
                if (frame > 1){
                    frame = 0;
                }

                try {
                    Thread.sleep(500);
                }catch (InterruptedException e){
                    e.printStackTrace();
                }
            }
        }
    }
}

但是当我尝试在我的手机上运行该应用程序(并触摸屏幕)时，我会返回到之前的 Activity 。截至目前，我无法在 android studio 中使用日志，所以我知道这是否是一个难以回答的问题。

Answer 1

您的 Point 触摸始终为 NULL，不是吗？可能你忘了初始化它:

touch = new Point();

如果没有这一行，变量 touch 始终为 null，因此当调用 onTouch() 时，Logcat 会说: java.lang.NullPointerException:尝试写入空对象引用上的字段“int android.graphics.Point.x”

所以在 onCreate() 或在 onTouch() 调用之前可以初始化的地方添加上面的行，希望这会有所帮助。