Create blurry transparent background effect

I am trying to make a view that will have a background that is not only transparent, but will also have a blur effect. That way the views underneath appear to be out of focus. I want it to look like the screen does after holding down the power button. Any ideas?

Now that the window flag is deprecated, you've got to blur yourself. I answered this elsewhere but here is how you can blur a view:

You can now use ScriptIntrinsicBlur from the RenderScript library to blur quickly. Here is how to access the RenderScript API. The following is a class I made to blur Views and Bitmaps:

import android.support.v8.renderscript.*;

public class BlurBuilder {
    private static final float BITMAP_SCALE = 0.4f;
    private static final float BLUR_RADIUS = 7.5f;

    public static Bitmap blur(View v) {
	    return blur(v.getContext(), getScreenshot(v));
    }

    public static Bitmap blur(Context ctx, Bitmap image) {
	    int width = Math.round(image.getWidth() * BITMAP_SCALE);
	    int height = Math.round(image.getHeight() * BITMAP_SCALE);

	    Bitmap inputBitmap = Bitmap.createScaledBitmap(image, width, height, false);
	    Bitmap outputBitmap = Bitmap.createBitmap(inputBitmap);

	    RenderScript rs = RenderScript.create(ctx);
	    ScriptIntrinsicBlur theIntrinsic = ScriptIntrinsicBlur.create(rs, Element.U8_4(rs));
	    Allocation tmpIn = Allocation.createFromBitmap(rs, inputBitmap);
	    Allocation tmpOut = Allocation.createFromBitmap(rs, outputBitmap);
	    theIntrinsic.setRadius(BLUR_RADIUS);
	    theIntrinsic.setInput(tmpIn);
	    theIntrinsic.forEach(tmpOut);
	    tmpOut.copyTo(outputBitmap);

	    return outputBitmap;
    }

    private static Bitmap getScreenshot(View v) {
	    Bitmap b = Bitmap.createBitmap(v.getWidth(), v.getHeight(), Bitmap.Config.ARGB_8888);
	    Canvas c = new Canvas(b);
	    v.draw(c);
	    return b;
    }
}

To apply this to a fragment, add the following to onCreateView:

final Activity activity = getActivity();
final View content = activity.findViewById(android.R.id.content).getRootView();
if (content.getWidth() > 0) {
	Bitmap image = BlurBuilder.blur(content);
	window.setBackgroundDrawable(new BitmapDrawable(activity.getResources(), image));
} else {
	content.getViewTreeObserver().addOnGlobalLayoutListener(new OnGlobalLayoutListener() {
		@Override
		public void onGlobalLayout() {
			Bitmap image = BlurBuilder.blur(content);
			window.setBackgroundDrawable(new BitmapDrawable(activity.getResources(), image));
		}
	});
}

NOTE: This solution requires min sdk to be API 17

EDIT: Renderscript is included into support v8 enabling this answer down to api 8. To enable it using gradle include these lines into your gradle file (from this answer) and use Renderscript from package android.support.v8.renderscript:

android {
  ...
  defaultConfig {
    ...
    renderscriptTargetApi *your target api*
    renderscriptSupportModeEnabled true
  }
  ...
}

If all you want to do is blur the background of the window behind your activty then you can use this call from within your activity (or any class, like an AlertDialog that has a window)

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

Update: this flag was deprecated in Android 4.0 and no longer works.

Blurry is a nice option which will easily give you the effect you are looking for: https://github.com/wasabeef/Blurry

after adding it to project, wrap the view you want to blur in a FrameLayout, then use this line when you want to blur:

Blurry.with(this).radius(25).sampling(2).onto((ViewGroup) findViewById(R.id.viewToBlurWrapper));