[英]Canceling AsyncTask from AsyncTask ProgressDialog
(这与nullpointer无关):我在AsyncTask中有一个进度条,并且添加了一个Cancel按钮来取消asynctask。
我可以从asynctask外部取消asynctask,但是我需要在progressdialog中实现cancel函数,该功能是在asynctask下实现的。
那么问题是如何使用在asynctask下的progressdialog中实现的cancel按钮取消asynctask?
请做检查“ doInBackground” .. asynctask没有得到取消
Download_result.java类:
public class Download_result extends AsyncTask<String,Integer,Void>{
ProgressDialog progressDialog;
Context context;
String pdfFile;
Download_result(Context context, String pdfFile){
this.context=context;
this.pdfFile=pdfFile;
}
@Override
protected void onPreExecute() {
progressDialog = new ProgressDialog(context);
progressDialog.setTitle("Downloading...");
progressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
progressDialog.setMax(200);
progressDialog.setCancelable(false);
progressDialog.setProgress(0);
progressDialog.setButton(DialogInterface.BUTTON_NEGATIVE, "Cancel", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
Download_result.this.cancel(true);
dialog.dismiss();
}
});
progressDialog.show();
}
@Override
protected Void doInBackground(String... params) {
//given below
}
@Override
protected void onProgressUpdate(Integer... values) {
progressDialog.setProgress(values[0]);
}
@Override
protected void onPostExecute(Void result) {
progressDialog.cancel();
}
}
我的“ doInBackground”方法:
@Override
protected Void doInBackground(String... params) {
String url_1=params[0];
int file_length=0;
try {
URL url = new URL(url_1);
URLConnection urlConnection = url.openConnection();
urlConnection.connect();
file_length=urlConnection.getContentLength();
filesize=file_length;
File sdCard = Environment.getExternalStorageDirectory();
File new_folder = new File (sdCard.getAbsolutePath() + "/xxx");
File input_file = new File(new_folder,pdfFile);
InputStream inputStream = new BufferedInputStream(url.openStream(),8192);
byte[] data=new byte[1024];
int total=0,count=0;
OutputStream outputStream = new FileOutputStream(input_file);
while ((count=inputStream.read(data))!=-1){
total+=count;
outputStream.write(data,0,count);
int progress= (total*200)/file_length;
downloadedsize=total;
publishProgress(progress);
if(isCancelled()){
break; or return null; // same result
}
}
inputStream.close();
outputStream.close();
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
return null;//"Download completed!";
}
您尚未取消按取消按钮中的对话框。也请使用setButton
代替
尝试这个:
@Override
protected void onPreExecute() {
progressDialog = new ProgressDialog(context);
progressDialog.setTitle("Downloading...");
progressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
progressDialog.setMax(200);
progressDialog.setCancelable(false);
progressDialog.setProgress(0);
progressDialog.setButton(DialogInterface.BUTTON_NEGATIVE, "Cancel", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
download.cancel(true);
downloadstatus=false; //add boolean check
dialog.dismiss();
}
});
progressDialog.show();
}
要取消异步任务,请使用:
Public Download_result download;
download = new Download_result();
download.execute();
download.cancel(true);
在doInbackGround
()中尝试一下
while ((count=inputStream.read(data))!=-1){
if(!your_AsyncTask.isCancelled() || downloadstatus !=false){
total+=count;
outputStream.write(data,0,count);
int progress= (total*200)/file_length;
downloadedsize=total;
publishProgress(progress);
}else{
break;
}
}
Download_result(Context context, String pdfFile,Download_result download)
将Download_result
作为参数发送到其自己的构造函数没有任何意义。 您永远不会有有效的引用来传递构造函数。 您应该将此构造函数更改为
Download_result(Context context, String pdfFile)
Download_result
每个方法已经具有对名为this
的Download_result
对象的引用。 由于您需要在内部类中访问它,因此请使用Download_result.this
:
progressDialog.setButton(DialogInterface.BUTTON_NEGATIVE, "Cancel", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
Download_result.this.cancel(true);
dialog.dismiss();
}
});
在AsyncTask中创建一个“ boolean keepGoing”并将其设置为true。 在您的“ doInBackground”过程中,定期对其进行轮询并返回(如果为false)。 将取消按钮绑定到AsyncTask中的设置器,该设置器将“ keepGoing”标志设置为false。 那应该做的。
在ProgressDialog的按钮上使用DialogInterface侦听器,例如:
protected void onPreExecute() {
pd = new ProgressDialog(MainActivity.this);
pd.setTitle("PAUL app");
pd.setMessage("Loading data ...");
pd.setButton("Cancel", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
// User has cancelled task ... just quit!
MainActivity.this.finish();
return;
}
});
pd.show();
}
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