进度对话框未显示在异步任务android中

Question

I am using Facebook SDK to upload photos to Facebook. While the photos are uploading I want to show a progress dialog, and I am facing a strange issue.

When I declare the ProgressDialog in the onPreExecute() method, the dialog box is shown.

protected void onPreExecute() {
    super.onPreExecute();
    ProgressDialog dialog = new ProgressDialog(Second.this);
    dialog.setProgressStyle(ProgressDialog.STYLE_SPINNER);
    dialog.setCancelable(true);
    dialog.setMessage("Uploading...");
    dialog.show();
}

But when I declare it globally, then nothing happens.

class newPhotoUpload extends AsyncTask<Void, Void, Void> {
    ProgressDialog dialog = new ProgressDialog(Second.this);
    Intent viewIntent;
    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        dialog.setProgressStyle(ProgressDialog.STYLE_SPINNER);
        dialog.setCancelable(true);
        dialog.setMessage("Uploading...");
        dialog.show();
    }

Why is this happening??

Answer 1

Put your progress bar as a global variable (below MainActivity extends Activity ) like,

ProgressDialog dialog=null;

Then

class newPhotoUpload extends AsyncTask<Void, Void, Void> {

    Intent viewIntent;
    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        dialog = new ProgressDialog(Second.this);
        dialog.setProgressStyle(ProgressDialog.STYLE_SPINNER);
        dialog.setCancelable(true);
        dialog.setMessage("Uploading...");
        dialog.show();
    }