利用java代码设置宽度:

 //设置宽度
        WindowManager m = getWindow().getWindowManager();
        Display d  =m.getDefaultDisplay();
        WindowManager.LayoutParams p =getWindow().getAttributes();
        Point size = new Point();
        d.getSize(size);
        p.width = (int)(size.x*0.8);//设置dialog的宽度为当前手机屏幕的宽度*0.8
        getWindow().setAttributes(p);