下面是我尝试通过 onProgressUpdate 方法在 Asynctask 中显示进度的代码，但它不会显示在警报对话框中。仅显示初始消息。
class DownloadFileFromURL extends AsyncTask<String, String, String> {
private AlertDialog.Builder alert;
private int progress = 0;
/**
* Before starting background thread Show Progress Bar Dialog
*/
@Override
protected void onPreExecute() {
super.onPreExecute();
alert = new AlertDialog.Builder(context);
alert.setTitle("Downloading..");
alert.setMessage("1");
alert.setCancelable(false);
alert.show();
}
/**
* Downloading file in background thread
*/
@Override
protected String doInBackground(String... f_url) {
int count;
try {
URL url = new URL(f_url[0]);
URLConnection conection = url.openConnection();
conection.connect();
// this will be useful so that you can show a tipical 0-100%
// progress bar
int lenghtOfFile = conection.getContentLength();
// download the file
InputStream input = new BufferedInputStream(url.openStream(),
8192);
// Output stream
OutputStream output = new FileOutputStream(file);
byte data[] = new byte[1024];
long total = 0;
while ((count = input.read(data)) != -1) {
total += count;
// publishing the progress....
// After this onProgressUpdate will be called
publishProgress("" + (int) ((total * 100) / lenghtOfFile));
// writing data to file
output.write(data, 0, count);
}
// flushing output
output.flush();
// closing streams
output.close();
input.close();
} catch (Exception e) {
Log.e("Error: ", e.getMessage());
}
return null;
}
/**
* Updating progress bar
*/
@Override
protected void onProgressUpdate(String... progress) {
Log.d("Myapp","progress :"+progress[0]);
alert.setMessage(""+progress[0]);
}
/**
* After completing background task Dismiss the progress dialog
**/
@Override
protected void onPostExecute(String file_url) {
// dismiss the dialog after the file was downloaded
}
}
由于我还编写了一个日志来显示 onProgressUpdate 中的进度更新，因此打印了日志，但 onProgressUpdate 中的alert.setMessage 似乎没有将消息设置到我的警报对话框中。
根据你的代码，alert is an AlertDialog.Builder而不是一个AlertDialog本身。这引起了我的担忧，因为它可能不会改变的原因是你已经向构建器展示了，但没有给AlertDialog。所以我尝试了一个简单的代码：
public class MainActivity extends AppCompatActivity {
private AlertDialog.Builder alert;
private AlertDialog ad;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
alert = new AlertDialog.Builder(this);
alert.setTitle("Downloading..");
alert.setMessage("1");
alert.setCancelable(false);
ad = alert.show();
Log.d("SAMPLE", "SET MESSAGE 2");
alert.setMessage("2");
Log.d("SAMPLE", "SET MESSAGE 3");
ad.setMessage("3");
}
}
起初，我只是使用alert.setMessage（这是AlertDialog.Builder），并且消息根本没有改变。但将其放入后AlertDialog然后设置消息AlertDialog例如，消息发生了变化。小心尝试一下这种方法。通过AlertDialog.Builder to an AlertDialog首先然后setMessage使用AlertDialog实例。
文档用于警报对话框 http://developer.android.com/reference/android/app/AlertDialog.html and AlertDialog.Builder http://developer.android.com/reference/android/app/AlertDialog.Builder.html.
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