Android make a dialog appear in fullscreen

here set your screen width and width to the dialog

WindowManager.LayoutParams lp = new WindowManager.LayoutParams();
    lp.copyFrom(dialog.getWindow().getAttributes());
    lp.width = width;
    lp.height = height;
    dialog.getWindow().setAttributes(lp);

or in your styles create a style like this then

 <style name="DialogTheme" parent="android:Theme.Dialog">

    <item name="android:layout_width">fill_parent</item>
    <item name="android:layout_height">fill_parent</item>


    <!-- No backgrounds, titles or window float -->
    <item name="android:windowBackground">@null</item>
    <item name="android:windowNoTitle">true</item>
    <item name="android:windowIsFloating">false</item>
</style>

create a dialog object like this

dialog = new Dialog(this, R.style.DialogTheme);

Edit ::

get width and height like this for any device it will fills..

WindowManager manager = (WindowManager) getSystemService(Activity.WINDOW_SERVICE);
    int width, height;
    LayoutParams params;

    if (Build.VERSION.SDK_INT > VERSION_CODES.FROYO) {
        width = manager.getDefaultDisplay().getWidth();
        height = manager.getDefaultDisplay().getHeight();
    } else {
        Point point = new Point();
        manager.getDefaultDisplay().getSize(point);
        width = point.x;
        height = point.y;
    }

first Make custom style for dialog in style.xml file:

<style name="full_screen_dialog" parent="@android:style/Theme.Dialog">
    <item name="android:windowNoTitle">true</item>
    <item name="android:windowFullscreen">true</item>
    <item name="android:windowIsFloating">true</item>
    <item name="android:windowContentOverlay">@null</item>
    <item name="android:windowAnimationStyle">@android:style/Animation.Dialog</item>
    <item name="android:windowSoftInputMode">stateUnspecified|adjustPan</item>
    <item name="android:windowBackground">@android:color/transparent</item>
</style>

Then after set this theme to your Alert Dialog:

 AlertDialog.Builder builder = new AlertDialog.Builder(new ContextThemeWrapper(this,  R.style.full_screen_dialog));

Or You can call new Activity and Give this Custom style to that activity as a theme in your manifest file...