问对话框在主屏幕上显示30秒后不显示

EN

 package com.example.homescreendialog;
    
    import androidx.appcompat.app.AppCompatActivity;
    
    import android.app.AlarmManager;
    import android.app.PendingIntent;
    import android.content.Intent;
    import android.os.Bundle;
    import android.os.SystemClock;
    import android.view.View;
    import android.widget.Button;
    
    public class MainActivity extends AppCompatActivity {
        Button mAlertButton;
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
            mAlertButton = (Button)findViewById(R.id.ID_Alert_dialog);
            mAlertButton.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View arg0) {
    
                    //Alarm manager
    
                    long timestamp = 30000;
                    Intent intent = new Intent(getApplicationContext(), AlertDialogReceiver.class);
                    PendingIntent mAlarmSender = PendingIntent.getBroadcast(getApplicationContext(),
                            167, intent, PendingIntent.FLAG_UPDATE_CURRENT);
    
                    AlarmManager amgr = (AlarmManager) getApplicationContext()
                            .getSystemService(getApplicationContext().ALARM_SERVICE);
    
                    amgr.set(AlarmManager.ELAPSED_REALTIME_WAKEUP, SystemClock.elapsedRealtime() + timestamp,
                            mAlarmSender);
                }
            });
        }
    }

 package com.example.homescreendialog;
    
    import android.app.Activity;
    import android.app.AlertDialog;
    import android.os.Bundle;
    import android.view.LayoutInflater;
    import android.view.View;
    import android.widget.Button;
    
    public class AlertDialogClass extends Activity {
        AlertDialog.Builder mAlertDlgBuilder;
        AlertDialog mAlertDialog;
        View mDialogView = null;
        Button mOKBtn, mCancelBtn;
        @Override
        protected void onCreate(Bundle savedInstanceState) {
    
            super.onCreate(savedInstanceState);
    
            //setContentView(R.layout.activity_main);
    
            LayoutInflater inflater = getLayoutInflater();
    
            mAlertDlgBuilder = new AlertDialog.Builder(this);
            mDialogView = inflater.inflate(R.layout.dialog_layout, null);
            mOKBtn = (Button)mDialogView.findViewById(R.id.ID_Ok);
            mCancelBtn = (Button)mDialogView.findViewById(R.id.ID_Cancel);
            mOKBtn.setOnClickListener(mDialogbuttonClickListener);
            mCancelBtn.setOnClickListener(mDialogbuttonClickListener);
            mAlertDlgBuilder.setCancelable(false);
            mAlertDlgBuilder.setInverseBackgroundForced(true);
            mAlertDlgBuilder.setView(mDialogView);
            mAlertDialog = mAlertDlgBuilder.create();
            mAlertDialog.show(); 
        }
      View.OnClickListener mDialogbuttonClickListener = new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if(v.getId() == R.id.ID_Ok) {
                    mAlertDialog.dismiss();
                    finish();
                } else if(v.getId() == R.id.ID_Cancel) {
                    mAlertDialog.dismiss();
                    finish();
                }
            }
        };
    }

package com.example.homescreendialog;

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;

public class AlertDialogReceiver extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {
        Intent alarmIntent = new Intent("android.intent.action.MAIN");
        alarmIntent.setClass(context, AlertDialogClass.class);
        alarmIntent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        context.startActivity(alarmIntent);
    }
}