before call setContext() method, you've to insert following code.
in java file.
[sourcecode language="JAVA"]
WindowManager.LayoutParams lpWindow = new WindowManager.LayoutParams();
lpWindow.flags = WindowManager.LayoutParams.FLAG_DIM_BEHIND;
lpWindow.dimAmount = 0.0f;
getWindow().setAttributes(lpWindow);
[/sourcecode]
in manifest file.
[sourcecode language="xml"]

[/sourcecode]