Custom screen dim with Dialog

This solution did not work for me. There is another option, you can cancel the flag that control dimming. This code worked for me:

dialog.getWindow().clearFlags(WindowManager.LayoutParams.FLAG_DIM_BEHIND);

Yes, it is. You can control it.

After creating dialog:

WindowManager.LayoutParams lp = dialog.getWindow().getAttributes();  
lp.dimAmount = 0.0f; // Dim level. 0.0 - no dim, 1.0 - completely opaque
dialog.getWindow().setAttributes(lp);

Upd: you can even add blur behind the dialog:

dialog.getWindow().addFlags(WindowManager.LayoutParams.FLAG_BLUR_BEHIND);

Upd2: Blurring is deprecated since API14:

This constant was deprecated in API level 14.
Blurring is no longer supported.

Answering it quite late but I am sure things get deprecated with time so my answer would definitely help someone. First of all create a dialog:

dialog = new Dialog(ActivityName.this);
dialog .setCancelable(false);
dialog .setContentView(R.layout.dialog_layout);

Then get the window of that dialog and add a flag called FLAG_DIM_BEHIND and finally set the dim amount on the screen.

Window window = dialog.getWindow();
if(window != null){
   window.addFlags(WindowManager.LayoutParams.FLAG_DIM_BEHIND); // This flag is required to set otherwise the setDimAmount method will not show any effect
   window.setDimAmount(0.5f); //0 for no dim to 1 for full dim
}

Then show your dialog,

dialog.show();

And before you dismiss your dialog, clear the flags:

dialog.getWindow().clearFlags(WindowManager.LayoutParams.FLAG_DIM_BEHIND);

And then dismiss:

dialog.dismiss();

Or you can do:

dialog.getWindow().setDimAmount(0.5f);