ProgressDialog新活动Asynctask未显示,为什么?

我使用以下代码创建了一个AsyncTask类

public class removeDialog extends AsyncTask<Void, Void, Void> {

Context c;
ProgressDialog asyncDialog;
String page;

public removeDialog(Context c, String page) {
    this.c = c;
    this.page = page;

    asyncDialog = new ProgressDialog(c);
}

@Override
protected void onPreExecute() {
    //set message of the dialog
    asyncDialog.setTitle("Please wait");
    asyncDialog.setMessage("Loading...");
    asyncDialog.setCancelable(false);
    //show dialog
    asyncDialog.show();

    if (page == "algemeneVoorwaarden") {
        Intent intent = new Intent(c, algemeneVoorwaarden.class);
        c.startActivity(intent);
    }
    if (page == "contact") {
        Intent intent = new Intent(c, contactTest.class);
        c.startActivity(intent);
    }

    super.onPreExecute();
}

@Override
protected Void doInBackground(Void... arg0) {

    //don't touch dialog here it'll break the application
    //do some lengthy stuff like calling login webservice

    return null;
}

@Override
protected void onPostExecute(Void result) {
    //hide the dialog
    asyncDialog.dismiss();

    super.onPostExecute(result);
}
}

我第一次尝试: 第一次我看到ProgressDialog,但第二次我想打开活动时,我什么也没有得到。

我第二次尝试: 即使是第一次尝试,我也没有得到任何进展。

我在异步任务类中执行代码,代码:

voorwaarden.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                new removeDialog(c, "algemeneVoorwaarden").execute();
            }
        });

有人知道为什么它不工作吗?请帮助我。