如何使用对话框按钮取消在android中下载的文件？

Question

public class ExampleActivity extends Activity {

    public static final int DIALOG_DOWNLOAD_PROGRESS = 0;
    private Button startBtn;
    private ProgressDialog mProgressDialog;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        startBtn = (Button)findViewById(R.id.startBtn);
        startBtn.setOnClickListener(new OnClickListener(){
            public void onClick(View v) {
                startDownload();
            }
        });
    }

    private void startDownload() {
        String url = "http://farm1.static.flickr.com/114/298125983_0e4bf66782_b.jpg";
        new DownloadFileAsync().execute(url);
    }


    @Override
    protected Dialog onCreateDialog(int id) {
        switch (id) {
        case DIALOG_DOWNLOAD_PROGRESS:
            mProgressDialog = new ProgressDialog(this);
            mProgressDialog.setMessage("Downloading file..");
            mProgressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
            mProgressDialog.setCancelable(true);
            mProgressDialog.setButton("Cancel", new CancelOnClickListener());

            mProgressDialog.show();
            return mProgressDialog;
        default:
            return null;
        }

    }
    private final class CancelOnClickListener implements DialogInterface.OnClickListener {
        public void onClick(DialogInterface dialog, int which) {
        ExampleActivity.this.finish();
        dismissDialog(DIALOG_DOWNLOAD_PROGRESS);
        new DownloadFileAsync().cancel(true);
    }

    }

class DownloadFileAsync extends AsyncTask<String, String, String> {

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        showDialog(DIALOG_DOWNLOAD_PROGRESS);
    }

    @Override
    protected String doInBackground(String... aurl) {
        int count;

    try 
    {
    URL url = new URL(aurl[0]);
    URLConnection conexion = url.openConnection();
    conexion.connect();

    int lenghtOfFile = conexion.getContentLength();
    Log.d("ANDRO_ASYNC", "Lenght of file: " + lenghtOfFile);

    InputStream input = new BufferedInputStream(url.openStream());
    OutputStream output = new FileOutputStream("/sdcard/some_photo_from_gdansk_poland.jpg");

    byte data[] = new byte[1024];

    long total = 0;

        while ((count = input.read(data)) != -1) {
            total += count;
            publishProgress(""+(int)((total*100)/lenghtOfFile));
            output.write(data, 0, count);
        }

        output.flush();
        output.close();
        input.close();
    }
    catch (Exception e) {

    }
    return null;

    }
    protected void onProgressUpdate(String... progress) {
         Log.d("ANDRO_ASYNC",progress[0]);
         mProgressDialog.setProgress(Integer.parseInt(progress[0]));
    }

    @Override
    protected void onPostExecute(String unused) {
        dismissDialog(DIALOG_DOWNLOAD_PROGRESS);
    }


 }
}

如果我点击开始按钮，它将自动下载文件。但我想取消下载（如果我不喜欢），所以我输入mProgressDialog.setButton("Cancel", new CancelOnClickListener());this 退出应用程序。但文件正在下载.如何改变doInBackground()里面的函数

Answer 1

您在startDownload() 和CancelOnClickListener 中使用了DownloadFileAsync 的两个不同实例。试试下面的代码：

public class ExampleActivity extends Activity {

public static final int DIALOG_DOWNLOAD_PROGRESS = 0;
private Button startBtn;
private ProgressDialog mProgressDialog;

DownloadFileAsync dfa = new DownloadFileAsync();

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    startBtn = (Button)findViewById(R.id.startBtn);
    startBtn.setOnClickListener(new OnClickListener(){
        public void onClick(View v) {
            startDownload();
        }
    });
}

private void startDownload() {
    String url = "http://farm1.static.flickr.com/114/298125983_0e4bf66782_b.jpg";
    dfa.execute(url);
}


@Override
protected Dialog onCreateDialog(int id) {
    switch (id) {
    case DIALOG_DOWNLOAD_PROGRESS:
        mProgressDialog = new ProgressDialog(this);
        mProgressDialog.setMessage("Downloading file..");
        mProgressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
        mProgressDialog.setCancelable(true);
        mProgressDialog.setButton("Cancel", new CancelOnClickListener());

        mProgressDialog.show();
        return mProgressDialog;
    default:
        return null;
    }

}
private final class CancelOnClickListener implements DialogInterface.OnClickListener {
    public void onClick(DialogInterface dialog, int which) {
    ExampleActivity.this.finish();
    dismissDialog(DIALOG_DOWNLOAD_PROGRESS);
    dfa.cancel(true);
}

}

class DownloadFileAsync extends AsyncTask<String, String, String> {

@Override
protected void onPreExecute() {
    super.onPreExecute();
    showDialog(DIALOG_DOWNLOAD_PROGRESS);
}

@Override
protected String doInBackground(String... aurl) {
    int count;

try 
{
URL url = new URL(aurl[0]);
URLConnection conexion = url.openConnection();
conexion.connect();

int lenghtOfFile = conexion.getContentLength();
Log.d("ANDRO_ASYNC", "Lenght of file: " + lenghtOfFile);

InputStream input = new BufferedInputStream(url.openStream());
OutputStream output = new FileOutputStream("/sdcard/some_photo_from_gdansk_poland.jpg");

byte data[] = new byte[1024];

long total = 0;
if(!isCancelled()){
    while (!isCancelled() && (count = input.read(data)) != -1) {
        total += count;
        publishProgress(""+(int)((total*100)/lenghtOfFile));
        output.write(data, 0, count);
    }

    output.flush();
    output.close();
    input.close();
}
}
catch (Exception e) {

}
return null;

}
protected void onProgressUpdate(String... progress) {
     Log.d("ANDRO_ASYNC",progress[0]);
     mProgressDialog.setProgress(Integer.parseInt(progress[0]));
}

@Override
protected void onPostExecute(String unused) {
    dismissDialog(DIALOG_DOWNLOAD_PROGRESS);
}


}
}