谁能帮助我解决asynctask中的错误?我想我知道为什么会出现错误,但是我不知道该怎么解决。非常感谢你。
这是我的asynctask代码(只想使用Surfaceview将其用于操纵杆)
public class MySurfaceThread extends AsyncTask<Void, Void, Void> {
SurfaceHolder mSurfaceHolder;
CustomSurfaceView cSurfaceView;
public MySurfaceThread(SurfaceHolder sh, CustomSurfaceView csv) {
mSurfaceHolder = sh;
cSurfaceView = csv;
x = y = 0;
cSurfaceView.setOnTouchListener(new OnTouchListener() {
@Override
public boolean onTouch(View v, MotionEvent event) {
x = event.getX();
y = event.getY();
calculateValues(x, y);
switch (event.getAction() & MotionEvent.ACTION_MASK) {
case MotionEvent.ACTION_DOWN:
break;
case MotionEvent.ACTION_UP:
x = y = 0;
dx = dy = 0;
break;
case MotionEvent.ACTION_CANCEL:
break;
case MotionEvent.ACTION_MOVE:
break;
}
return true;
}
private void calculateValues(float xx, float yy) {
dx = xx - zeroX;
dy = yy - zeroY;
angle = (float)Math.atan(Math.abs(dy/dx));
hyp = (float)Math.sqrt((dx * dx) + (dy * dy));
if(hyp > radius) {
if(dx > 0 && dy > 0){ //bottom right
xx = (zeroX + (radius*(float)Math.cos(angle)));
yy = (zeroY + (radius*(float)Math.sin(angle)));
}
else if(dx > 0 && dy < 0){ //top right
xx = (zeroX + (radius*(float)Math.cos(angle)));
yy = (zeroY - (radius*(float)Math.sin(angle)));
}
else if(dx < 0 && dy < 0){ //top left
xx = (zeroX - (radius*(float)Math.cos(angle)));
yy = (zeroY - (radius*(float)Math.sin(angle)));
}
else if(dx < 0 && dy > 0) { //bottom left
xx = (zeroX - (radius*(float)Math.cos(angle)));
yy = (zeroY + (radius*(float)Math.sin(angle)));
}
}
else {
xx = zeroX + dx;
yy = zeroY + dy;
}
x = xx;
y = yy;
}
});
}
@Override
protected Void doInBackground(Void... params) {
Canvas canvas = null;
while (running) {
try {
canvas = mSurfaceHolder.lockCanvas();
synchronized (mSurfaceHolder) {
zeroX = canvas.getWidth()/2;
zeroY = canvas.getHeight()/2;
cSurfaceView.onDraw(canvas, x, y, zeroX, zeroY);
}
Thread.sleep(10);
} catch (InterruptedException e) {
} finally {
if (canvas != null) {
mSurfaceHolder.unlockCanvasAndPost(canvas);
}
}
}
return null;
}
}
我可以使用runnable和thread来执行相同的任务吗?如果是这样,怎么办?谢谢你。
编辑
这是logcat中的错误消息:
03-09 15:23:52.394 4135-4159/com.example.r.bluetoothsample E/AndroidRuntime﹕ FATAL EXCEPTION: AsyncTask #1
Process: com.example.r.bluetoothsample, PID: 4135
java.lang.RuntimeException: An error occured while executing doInBackground()
at android.os.AsyncTask$3.done(AsyncTask.java:300)
at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355)
at java.util.concurrent.FutureTask.setException(FutureTask.java:222)
at java.util.concurrent.FutureTask.run(FutureTask.java:242)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
at java.lang.Thread.run(Thread.java:841)
Caused by: java.lang.NullPointerException
at com.example.r.bluetoothsample.CustomSurfaceView$MySurfaceThread.doInBackground(CustomSurfaceView.java:182)
at com.example.r.bluetoothsample.CustomSurfaceView$MySurfaceThread.doInBackground(CustomSurfaceView.java:95)
at android.os.AsyncTask$2.call(AsyncTask.java:288)
at java.util.concurrent.FutureTask.run(FutureTask.java:237)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
at java.lang.Thread.run(Thread.java:841)
最佳答案
如果您的表面不可用,那么 lockCanvas()
将返回null(我假设它在您离开 Activity 时会变为null)。这意味着您将在NullPointerException
调用中遇到getWidth()
。
附带说明,我希望您在 Activity 的running
方法中停止该后台循环(也许通过将false
设置为onPause()
吗?)-否则,它将继续在后台循环,这是不希望的。
关于java - 每当我单击“后退”/“主页”按钮时,代码的asynctask部分就会关闭/停止该应用程序,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/35885156/