设置对话框背景可绘制时，Android NullPointerException

问题描述

设置Dialogs背景可绘制时，我得到一个警告， 方法调用“ setBackgroundDrawable”可能会产生“ java.lang.NullPointerException” 。 我将如何防止此类异常？

class UIManager {

    private Context context;
    private MapActivity activity;
    private Dialog dialog;

    UIManager(MapActivity activity, Context context) {
        this.activity = activity;
        this.context = context;
        this.dialog = new Dialog(context);

        dialog.setContentView(R.layout.upload_dialog);

        /* THIS LINE */
        dialog.getWindow().setBackgroundDrawable(new ColorDrawable(Color.TRANSPARENT));

        dialog.setCancelable(false);
        dialog.setCanceledOnTouchOutside(false);
    }

    void showUploadDialog() {
        dialog.show();
    }

    void dismissUploadDialog() {
        dialog.dismiss();
    }
    ...
}