How to put AlertDialog in static method

Question

How to show Alert Dialog in static method, i am trying to put a condition, in which i am checking for the folder inside the SD Card, if exist then listing Items, otherwise i want to show AlertDialog - with message no folder found with Church Name

  public static List <String> fromSDCard()
    {
        List <String> listChurchWall = new ArrayList <String>();
        // listing Wallpaper using church names
        String string = "/mnt/sdcard/Church/Wallpaper/";
        f = new File (string+name+"/");
        if (f.exists()) 
         {
            files = f.listFiles ();
         }else{
        // here i want to put AlertDialog       
         }                          
    return listChurchWall;  
    }   

Answer 1

Pass your app context to the static method.

public static List <String> fromSDCard(Context context)
{
    List <String> listChurchWall = new ArrayList <String>();
    // listing Wallpaper using church names
    String string = "/mnt/sdcard/Church/Wallpaper/";
    f = new File (string+name+"/");
    if (f.exists()) 
     {
        files = f.listFiles ();
     }else{
         // 1. Instantiate an AlertDialog.Builder with its constructor
         AlertDialog.Builder builder = new AlertDialog.Builder(context);

         // 2. Chain together various setter methods to set the dialog characteristics
         builder.setMessage(R.string.dialog_message)
         .setTitle(R.string.dialog_title);

         // 3. Get the AlertDialog from create()
        AlertDialog dialog = builder.create();

        // 4. Show the dialog
        dialog.show()
     }                          
     return listChurchWall;  
}   

If calling from your activity.

public MyActivity extends Activity
{
    ....

    private void Method()
    {
         List<String> list = fromSdCard(this);
    }

    ....
}

Answer 2

public static List<String> fromSDCard(Context mContext) {
        List<String> listChurchWall = new ArrayList<String>();
        // listing Wallpaper using church names
        String string = "/mnt/sdcard/Church/Wallpaper/";
        f = new File(string + name + "/");
        if (f.exists()) {
            files = f.listFiles();
        } else {
            AlertDialog.Builder builder = new AlertDialog.Builder(mContext);

            int imageResource = android.R.drawable.stat_sys_warning;
            Drawable image = mContext.getResources().getDrawable(imageResource);

            builder.setTitle("title").setMessage("your Message").setIcon(image).setCancelable(false).setNeutralButton("Ok", new DialogInterface.OnClickListener() {
                public void onClick(DialogInterface dialog, int id) {
                }
            });

            AlertDialog alert = builder.create();
            alert.setCancelable(false);
            alert.show();
        }
        return listChurchWall;
    }

Answer 3

Try the following way--

public static List <String> fromSDCard(Activity a, String title, String message)
 {
    List <String> listChurchWall = new ArrayList <String>();
    // listing Wallpaper using church names
    String string = "/mnt/sdcard/Church/Wallpaper/";
    f = new File (string+name+"/");
    if (f.exists()) 
    {
      files = f.listFiles ();
    }
    else
    {
      AlertDialog.Builder dialog = new AlertDialog.Builder(a);
      dialog.setTitle(title);
      dialog.setMessage(message);
      dialog.setNeutralButton("OK", null);
      dialog.create().show();      
    }                          
    return listChurchWall;  
 }   

Then in your class do---

public MyActivity extends Activity
{
    ....

    private Method()
    {
         List<String> list = fromSdCard(this, "Your Title", "Your message");
    }

    ....
}

UPDATE:

You get a NullPointerException because something is null that shouldn't be. It happens while sorting the array, so perhaps one of the array elements is null. Take a look at how you assign values to your array.

Perhaps at the top of it, see if any of the objects Object o1 or Object o2 themselves are null.