dialog要改变其在window中的大小不同于普通的view，下面直接上代码

//在dialog.show()之后调用
public static void setDialogWindowAttr(Dialog dlg,Context ctx){
        Window window = dlg.getWindow();
        WindowManager.LayoutParams lp = window.getAttributes();
        lp.gravity = Gravity.CENTER;
        lp.width = LayoutParams.MATH_PARENT;//宽高可设置具体大小
        lp.height = LayoutParams.MATH_PARENT;
        dlg.getWindow().setAttributes(lp);
    }