我是 Android 新手，并不知道如何处理这个问题:我有一个 AsyncTask，它从 XML 文件中读取位置 (X,Y,Z)。由于这个位置每秒都在变化，我希望在我按下一个按钮(用“StartListener”调用)后连续读取和绘制每个新位置并在我再次按下按钮时停止读取它......
有人可以帮助我吗？ - 这是我的 MainActivity 的一部分
(目前我的应用程序仅在我按下按钮时读取和绘制位置...)
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
最佳答案
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() 中准备所有繁重的工作人员，在 doInBackground() 中读取 XML 并进行绘制，在onProgressUpdate() 最后，当任务完成时，将图像保存到 sdcard。
我已经修改了您的 Asynctask 来完成上述场景，我没有测试它，但它给了您想法。
在 Activity 的 onCreate() 方法中，您只需启动 AsyncTask 一次。它会一直执行或休眠，直到您将 Quit_Task 变量设置为 true。当按下按钮时，您切换变量 Do_Drawing: Do_Drawing=!Do_Drawing; 就这样。
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
关于Android 如何每秒运行一个 AsyncTask？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/18702298/