设置AlertDialog圆角背景，我已经加了圆角.9图，为什么是这种效果，不满意

我的代码
AlertDialog.Builder fenzudialog= new AlertDialog.Builder(getActivity());
fenzudialog.setView(fenzuadd);
fenzudialog.setPositiveButton("添加", new DialogInterface.OnClickListener() {

                @Override
                public void onClick(DialogInterface dialog, int which) {
                    bitmap=fenzuimage.getDrawingCache();
                    fenzunamestring=fenzuname.getText().toString();


                }
            });
    fenzudialog.setNegativeButton("取消", new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialog, int which) {

        }
    });
    fenzudialog.create();
    AlertDialog dialog=fenzudialog.show();
    WindowManager.LayoutParams layoutParams = dialog.getWindow().getAttributes();
    layoutParams.width = LinearLayout.LayoutParams.WRAP_CONTENT;
    layoutParams.height = LinearLayout.LayoutParams.WRAP_CONTENT;
    dialog.getWindow().setGravity(Gravity.TOP);
    dialog.getWindow().setBackgroundDrawableResource(R.drawable.image_yj);
    dialog.getWindow().setWindowAnimations(R.style.bottomdialogstyle);
    dialog.getWindow().setAttributes(layoutParams);

用Dialog吧，自定义方便一些