Handling ProgressBars
ProgressBar is used to display the progress of an activity while the user is waiting. You can display an indeterminate progress (spinning wheel) or result-based progress.
We can display an indeterminate progress bar which we show to indicate waiting:
<ProgressBar
android:id="@+id/pbLoading"
android:visibility="invisible"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />and then manage the visibility in the activity:
// on some click or some loading we need to wait for...
ProgressBar pb = (ProgressBar) findViewById(R.id.pbLoading);
pb.setVisibility(ProgressBar.VISIBLE);
// run a background job and once complete
pb.setVisibility(ProgressBar.INVISIBLE);Typically you want to try to put the ProgressBar in the place where data is going to show (i.e. as a placeholder for an image). For a ListView, you put the ProgressBar in the header or footer, which lets you put an arbitrary layout outside of the adapter.
ProgressBar can be used to report the progress of a long-running AsyncTask. In this case:
- ProgressBar can report numerical results for a task.
- Must specify horizontal style and result max value.
- Must
publishProgress(value)in your AsyncTask
<ProgressBar
android:id="@+id/progressBar1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:visibility="invisible"
style="?android:attr/progressBarStyleHorizontal"
android:max="100" />and then within the AsyncTask:
public class DelayTask extends AsyncTask<Void, Integer, String> {
int count = 0;
@Override
protected void onPreExecute() {
pb.setVisibility(ProgressBar.VISIBLE);
}
@Override
protected String doInBackground(Void... params) {
while (count < 5) {
SystemClock.sleep(1000); count++;
publishProgress(count * 20);
}
return "Complete";
}
@Override
protected void onProgressUpdate(Integer... values) {
pb.setProgress(values[0]);
}
}and using this pattern any background tasks can be reflected by an on-screen progress report.