我是Android的新手，并不知道如何处理这个问题：我有一个AsyncTask从XML文件中读取位置（X，Y，Z）。由于这个位置每秒都会改变，我想按下一个按钮（用“StartListener”调用）来连续读取和绘制每个新位置，当我再次按下按钮时停止读取它...
有人可以帮帮我吗？ - 这是我的MainActivity的一部分
（目前我的应用程序只有在按下按钮时才会读取并绘制位置...）
private OnClickListener StartListener = new OnClickListener() {
@Override
public void onClick(View v) {
TextView ButText = (TextView)findViewById(R.id.buttonStart);
String value=ButText.getText().toString();
if(value.equals("Start positioning")){
ButText.setText("Stop positioning");
new PositionAsync().execute(); //read data from XML file
}
else if(value.equals("Stop positioning")){
ButText.setText("Start positioning");
//new PositionAsync().cancel(true);
}
}
}; // END LISTENER START BUTTON
// READ XML FILE
class PositionAsync extends AsyncTask<Void, Void, Void> {
XMLHelper helper;
@Override
protected Void doInBackground(Void... arg0) {
helper = new XMLHelper();
helper.get();
return null;
}
@Override
protected void onPostExecute(Void result) {
Paint paintBlack = new Paint(); paintBlack.setAntiAlias(true); paintBlack.setColor(Color.BLACK);
BitmapFactory.Options myOptions = new BitmapFactory.Options();
myOptions.inDither = true;
myOptions.inScaled = false;
myOptions.inPreferredConfig = Bitmap.Config.ARGB_8888;// important
myOptions.inPurgeable = true;
File ImageSource = new File("/sdcard/app_background3.jpg");
Bitmap bitmap2 = BitmapFactory.decodeFile(ImageSource.getAbsolutePath(),myOptions);
Bitmap workingBitmap = Bitmap.createBitmap(bitmap2);
Bitmap mutableBitmap2 = workingBitmap.copy(Bitmap.Config.ARGB_8888, true);
Canvas canvas2 = new Canvas(mutableBitmap2);
float RoomWidthPx = canvas2.getWidth();
float RoomHeightPx = canvas2.getHeight();
float RoomXmeter = (float) 9.3;
float RoomZmeter = (float) 14.7;
for (PositionValue position : helper.positions) {
String PosX = position.getPositionX(); String PosY = position.getPositionY(); String PosZ = position.getPositionZ();
float x = Float.valueOf(PosX); float y = Float.valueOf(PosY); float z = Float.valueOf(PosZ);
float xm = x*RoomWidthPx/RoomXmeter;
float zm = z*RoomHeightPx/RoomZmeter;
canvas2.drawCircle(xm, zm, 25, paintBlack);
ImageView imageView = (ImageView)findViewById(R.id.imageView1);
imageView.setAdjustViewBounds(true);
imageView.setImageBitmap(mutableBitmap2);
// SAVE DRAWINGS INTO FILE
FileOutputStream fos = null;
try {
fos = new FileOutputStream ("/sdcard/app_background3.jpg");
mutableBitmap2.compress (Bitmap.CompressFormat.JPEG, 95, fos);
} catch (Throwable ex) {ex.printStackTrace (); }
};
}
} //END READ XML FILE
答案 0 :(得分：1)
您可以使用处理程序来处理此问题：
private boolean isBusy = false;//this flag to indicate whether your async task completed or not
private boolean stop = false;//this flag to indicate whether your button stop clicked
private Handler handler = new Handler();
public void startHandler()
{
handler.postDelayed(new Runnable()
{
@Override
public void run()
{
if(!isBusy) callAysncTask();
if(!stop) startHandler();
}
}, 1000);
}
private void callAysncTask()
{
//TODO
new PositionAsync().execute();
}
当您点击停止按钮设置停止为true时，点击开始按钮时将停止设置为false
答案 1 :(得分：1)
我认为你在一秒钟内完成了太多任务。相反，您可以在AsyncTask的onPreExecute()中准备好所有重要人员，阅读XML并在doInBackground()中进行绘制，在onProgressUpdate()中重新刷新ImageView，最后，任务完成后，将图像保存到sdcard。
我已经修改了你的Asynctask以完成上述情况，我没有对其进行测试，但它可以为您提供这个想法。
在您的活动的onCreate()方法中，您只启动一次AsyncTask。在您将Quit_Task变量设置为true之前，它将保持执行或休眠状态。按下按钮后，您可以切换变量Do_Drawing: Do_Drawing=!Do_Drawing;，就可以了。
private boolean Do_Drawing = false;
private boolean Quit_Task = false;
// READ XML FILE
class PositionAsync extends AsyncTask<Void, Void, Void>
{
Paint paintBlack;
BitmapFactory.Options myOptions;
Bitmap mutableBitmap2;
Canvas canvas2;
XMLHelper helper;
void Sleep(int ms)
{
try
{
Thread.sleep(ms);
}
catch (Exception e)
{
}
}
@Override
protected void onPreExecute()
{
// Prepare everything for doInBackground thread
paintBlack = new Paint();
paintBlack.setAntiAlias(true);
paintBlack.setColor(Color.BLACK);
myOptions = new BitmapFactory.Options();
myOptions.inDither = true;
myOptions.inScaled = false;
myOptions.inPreferredConfig = Bitmap.Config.ARGB_8888;// important
myOptions.inPurgeable = true;
File ImageSource = new File("/sdcard/app_background3.jpg");
Bitmap bitmap2 = BitmapFactory.decodeFile(ImageSource.getAbsolutePath(), myOptions);
Bitmap workingBitmap = Bitmap.createBitmap(bitmap2);
mutableBitmap2 = workingBitmap.copy(Bitmap.Config.ARGB_8888, true);
canvas2 = new Canvas(mutableBitmap2);
helper = new XMLHelper();
}
@Override
protected Void doInBackground(Void... arg0)
{
while (!Quit_Task)
{
// Sleep until button is pressed or quit
while (!Do_Drawing)
{
Sleep(1000);
if (Quit_Task)
return null;
}
float RoomWidthPx = canvas2.getWidth();
float RoomHeightPx = canvas2.getHeight();
float RoomXmeter = (float) 9.3;
float RoomZmeter = (float) 14.7;
// keep drawing until button is pressed again or quit
while (Do_Drawing)
{
if (Quit_Task)
return null;
helper.get();
for (PositionValue position : helper.positions)
{
String PosX = position.getPositionX();
String PosY = position.getPositionY();
String PosZ = position.getPositionZ();
float x = Float.valueOf(PosX);
float y = Float.valueOf(PosY);
float z = Float.valueOf(PosZ);
float xm = x * RoomWidthPx / RoomXmeter;
float zm = z * RoomHeightPx / RoomZmeter;
canvas2.drawCircle(xm, zm, 25, paintBlack);
}
this.publishProgress((Void) null);
Sleep(1000);
}
}
return null;
}
@Override
protected void onProgressUpdate(Void... progress)
{
// once all points are read & drawn refresh the imageview
try
{
ImageView imageView = (ImageView) findViewById(R.id.imageView1);
imageView.setAdjustViewBounds(true);
imageView.setImageBitmap(mutableBitmap2);
}
catch (Exception e)
{
e.printStackTrace();
}
}
@Override
protected void onPostExecute(Void result)
{
// SAVE DRAWINGS INTO FILE once the task is done.
FileOutputStream fos = null;
try
{
fos = new FileOutputStream(Environment.getExternalStorageDirectory().getPath() + "app_background3.jpg");
mutableBitmap2.compress(Bitmap.CompressFormat.JPEG, 95, fos);
}
catch (Throwable ex)
{
ex.printStackTrace();
}
}
} // END READ XML FILE