問題是當我進入游戲并單擊“主頁”按鈕時,gameLoop線程(我想)被弄亂了,然后彈出“不幸的是,“應用名稱”已停止”.

我已經制作了一個非常簡單的程序來解決此問題.該程序所做的全部工作就是在屏幕上顯示一個數字,并在您觸摸屏幕時增加它.

當我在GameLoopThread中注釋掉view.onDraw(c)時,一切似乎運行良好.

錯誤信息：

FATAL EXEPTION: Thread-23207

java.lang.NullPointerExeption

at com.example.crashtest.GameView.onDraw(GameView.java:61)

at com.example.crashtest.GameLoopThread.run(GameLoopThread.java:34)

這是代碼：

MainActivity.java

package com.example.crashtest;

import android.os.Bundle;

import android.app.Activity;

import android.content.res.Configuration;

import android.view.KeyEvent;

import android.view.Window;

public class MainActivity extends Activity {

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

requestWindowFeature(Window.FEATURE_NO_TITLE);

setContentView(new GameView(this));

}

@Override

public void onConfigurationChanged(Configuration newConfig) {

super.onConfigurationChanged(newConfig);

}

@Override

public boolean onKeyDown(int keyCode, KeyEvent event) {

switch (keyCode) {

case KeyEvent.KEYCODE_BACK:

return true;

case KeyEvent.KEYCODE_MENU:

return true;

case KeyEvent.KEYCODE_VOLUME_UP:

return true;

case KeyEvent.KEYCODE_VOLUME_DOWN:

return true;

default:

return false;

}

}

}

GameView.java

package com.example.crashtest;

import android.annotation.SuppressLint;

import android.content.Context;

import android.graphics.Canvas;

import android.graphics.Color;

import android.graphics.Paint;

import android.graphics.Paint.Align;

import android.view.MotionEvent;

import android.view.SurfaceHolder;

import android.view.SurfaceView;

public class GameView extends SurfaceView {

private SurfaceHolder holder;

private GameLoopThread gameLoopThread;

private int num = 0;

public GameView(final Context context) {

super(context);

holder = getHolder();

holder.addCallback(new SurfaceHolder.Callback() {

@Override

public void surfaceDestroyed(SurfaceHolder holder) {

boolean retry = true;

gameLoopThread.setRunning(false);

while (retry) {

try {

gameLoopThread.join();

retry = false;

} catch (InterruptedException e) {}

}

}

@Override

public void surfaceCreated(SurfaceHolder holder) {

makeThread();

gameLoopThread.start();

gameLoopThread.setRunning(true);

}

@Override

public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {

}

});

}

private void makeThread() {

gameLoopThread = new GameLoopThread(this);

}

@SuppressLint({ "WrongCall", "DrawAllocation" })

@Override

protected void onDraw(Canvas canvas) {

// Draw black background - Write variable 'num' on the screen

canvas.drawColor(Color.BLACK);

Paint paint = new Paint();

paint.setARGB(255, 0, 255, 0);

paint.setTextSize(50);

paint.setTextAlign(Align.CENTER);

canvas.drawText(Integer.toString(num), getWidth() / 2, getHeight() / 2, paint);

}

public boolean onTouchEvent(MotionEvent event) {

if(event.getAction() == MotionEvent.ACTION_DOWN) {

// Increase 'num' with 1 every touch

num++;

}

return super.onTouchEvent(event);

}

}

GameLoopThread.java

package com.example.crashtest;

import android.annotation.SuppressLint;

import android.graphics.Canvas;

public class GameLoopThread extends Thread {

static final long FPS = 10;

private GameView view;

public boolean running = false;

public boolean pause = false;

public GameLoopThread(GameView view) {

this.view = view;

}

public void setRunning(boolean run) {

running = run;

}

@SuppressLint("WrongCall")

@Override

public void run() {

long ticksPS = 1000 / FPS;

long startTime = 0;

long sleepTime = 0;

while (running) {

Canvas c = null;

startTime = System.currentTimeMillis();

try {

c = view.getHolder().lockCanvas();

synchronized (view.getHolder()) {

view.onDraw(c);

}

} finally {

if (c != null) {

view.getHolder().unlockCanvasAndPost(c);

}

}

sleepTime = ticksPS-(System.currentTimeMillis() - startTime);

try {

if (sleepTime > 0)

sleep(sleepTime);

else

sleep(10);

} catch (Exception e) {}

}

}

}

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