programmatically change layout height, ClassCastException?

The layout paramaters should be of the type of the parent of your view. For instance, if your WebView is inside a LinearLayout, use LinearLayout.LayoutParams.

use it-

ViewGroup.LayoutParams vc=webview.getLayoutParams();
        vc.height=700;
        vc.width=450;

        webview.setLayoutParams(vc);

It will work