AlertDialog is not shown when i create it with a AndroidDialog.Builder

i'm new to create dynamic dialog, and this is my issue:

When i show the dialog with builder.create().show(), everything works fine, but when I try to show after assign it to AlertDialog it doesn't show.

this is my code:

    final EnablerButton enablerPositiveButton=new EnablerButton(TextToMonitor);

    final AlertDialog.Builder builder = new AlertDialog.Builder(MyAct.this)
                          .setView(ll)
                          .setPositiveButton("Ok", new DialogInterface.OnClickListener() {

                             @Override
                            public void onClick(DialogInterface dialog, int whichButton) {
                                                        enablerPositiveButton.interrupt();

                                      ProgressDialog progressBar;



                                      progressBar = new ProgressDialog(parentActivity);
                                      progressBar.setCancelable(false);
                                      progressBar.setProgressStyle(ProgressDialog.STYLE_SPINNER);
                                      progressBar.setProgress(1);
                                      progressBar.setMax(10000);
                                      progressBar.show();


                                      }
             }).setCancelable(false);

    AlertDialog alert = builder.create();

    alert.getButton(AlertDialog.BUTTON_POSITIVE).setEnabled(false);
    enablerPositiveButton.setButtonToEnable(alert.getButton(AlertDialog.BUTTON_POSITIVE));
    enablerPositiveButton.start();
    alert.show();

And this is my thread that check if the fields are empty:

public class EnablerButton extends Thread {

public boolean run=true;
Button btnToEnable;
LinkedList <EditText> editTextsToCheck;


public EnablerButton(LinkedList<EditText> editTexts){

    this.editTextsToCheck = editTexts;
}

@Override
public void run(){

    while (run) {
        boolean alright = true;
        for (EditText editText : editTextsToCheck) {
            if (editText.getText().toString().isEmpty()) alright = false;
        }
        if (alright) btnToEnable.setEnabled(true);
        else btnToEnable.setEnabled(false);
        try {
            sleep(500);
        }catch(InterruptedException e){
            e.printStackTrace();
            run=false;
        }
    }
}

public void setButtonToEnable(Button toEnable){
    this.btnToEnable = toEnable;
}
public void interrupt(){
    run=false;
}


}