show an alert dialog in broadcast receiver after a system reboot

The problem is you are trying to show an AlertDialog from a BroadcastReceiver, which isn't allowed. You can't show an AlertDialog from a BroadcastReceiver. Only activities can display dialogs.

You should do something else, have the BroadcastReceiver start on boot as you do and start an activity to show the dialog.

Here is a blog post more on this.

EDIT:

Here is how I would recommend doing it. From your BroadcastReceiver start an Activity with an AlertDialog as such..

public class NotifySMSReceived extends Activity 
{
    private static final String LOG_TAG = "SMSReceiver";
    public static final int NOTIFICATION_ID_RECEIVED = 0x1221;
    static final String ACTION = "android.provider.Telephony.SMS_RECEIVED";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        IntentFilter filter = new IntentFilter(ACTION);
        this.registerReceiver(mReceivedSMSReceiver, filter);
    }

    private void displayAlert()
    {
        AlertDialog.Builder builder = new AlertDialog.Builder(this);
        builder.setMessage("Are you sure you want to exit?").setCancelable(
            false).setPositiveButton("Yes",
            new DialogInterface.OnClickListener() {
                public void onClick(DialogInterface dialog, int id) {
                    dialog.cancel();
                }
            }).setNegativeButton("No",
            new DialogInterface.OnClickListener() {
                public void onClick(DialogInterface dialog, int id) {
                    dialog.cancel();
                }
            });
        AlertDialog alert = builder.create();
        alert.show();
    }

    private final BroadcastReceiver mReceivedSMSReceiver = new BroadcastReceiver() {

        @Override
        public void onReceive(Context context, Intent intent) {
            String action = intent.getAction();

            if (ACTION.equals(action)) 
            {
                //your SMS processing code
                displayAlert();
            }
        }
    }
}

As you see here I NEVER called setContentView(). This is because the activity will have a transparent view and only the alert dialog will show.

You can't use dialog on BroadcastReceiver, so instead you better call an activity for the dialog box from the BroadcastReceiver,

add this code in your onReceive function :

@Override
public void onReceive(Context context, Intent intent) 
{
    Intent i = new Intent(context, {CLASSNAME}.class); 
    i.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK); 
    context.startActivity(i);
}

fill the {CLASSNAME} with the dialog activity, heres my dialog activity :

package com.example.mbanking;

import android.os.Bundle;
import android.app.Activity;
import android.app.AlertDialog;
import android.content.DialogInterface;


// ALERT DIALOG
// Sources : http://techblogon.com/alert-dialog-with-edittext-in-android-example-with-source-code/

public class AlertDialogActivity extends Activity 
{

@Override
protected void onCreate(Bundle savedInstanceState) 
{
    super.onCreate(savedInstanceState);

    AlertDialog.Builder builder = new AlertDialog.Builder(this);
    builder
        .setTitle("Test")
        .setMessage("Are you sure you want to exit?")
        .setCancelable(false)
        .setPositiveButton("Yes", new DialogInterface.OnClickListener() 
        {
            public void onClick(DialogInterface dialog, int id) 
            {
                dialog.cancel();
            }
        })
        .setNegativeButton("No", new DialogInterface.OnClickListener() 
        {
            public void onClick(DialogInterface dialog, int id) 
            {
                dialog.cancel();
            }
        });
    AlertDialog alert = builder.create();
    alert.show();
}
}

where I got the answer ?, here : How do you use an alert dialog box in a broadcast receiver in android? thanks to Femi !!, I just spread the news :D

Here is a post on how to do it. You can get the source code from here.

You can't show dialog directly from your broadcast receiver. You have to use an Activity. Also, in order to receive ACTION_BOOT_COMPLETED your activity must be first explicitly started by user or by another application (google application stopped state for more information).

Basically, to achieve the required functionality, you need to do:

1. Create transparent activity that shows dialog.
2. Create BroadcastReceiver that receives ACTION_BOOT_COMPLETED and starts your activity.
3. Register your broadcast receiver in the manifest and acquire a proper permission.

Also, this question provides more information on how to create a transparent activity.

The best way is to make an activity and set its "Theme" attribute to "Theme.Translucen"

 <activity
        android:name=".MyAlertDialog"
        android:label="@string/title_activity_alert_dialog"
        android:launchMode="singleInstance"
        android:theme="@android:style/Theme.Translucent" >
    </activity>

and in your activity create an Alert dialog:

public class MyAlertDialog extends Activity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    requestWindowFeature(Window.FEATURE_NO_TITLE); //hide activity title
    setContentView(R.layout.activity_my_alert_dialog);

    AlertDialog.Builder Builder=new AlertDialog.Builder(this)
            .setMessage("Do You Want continue ?")
            .setTitle("exit")
            .setIcon(android.R.drawable.ic_dialog_alert)
            .setNegativeButton(R.string.No, new DialogInterface.OnClickListener() {
                @Override
                public void onClick(DialogInterface dialog, int which) {
                    MyAlertDialog.this.finish();
                }
            })
            .setPositiveButton(R.string.Yes,null);
    AlertDialog alertDialog=Builder.create();
    alertDialog.show();

}

}

and in brodcastreciver:

 @Override
public void onReceive(Context context, Intent intent) {

    Intent i=new Intent(context.getApplicationContext(),MyAlertDialog.class);
    i.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
    context.startActivity(i);

}
}