Android阻止AlertDialog关闭

 AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
 builder.setTitle("测试");

 LayoutInflater inflater = getActivity().getLayoutInflater();
 View view = inflater.inflate(R.layout.dialogfragment_num_input, null);
 builder.setView(view);

 builder.setPositiveButton("确定",
         new DialogInterface.OnClickListener() {
             @Override
             public void onClick(DialogInterface dialog, int id) {

                 Field field = null;

                 try {
                     //通过反射获取dialog中的私有属性mShowing
                     field = dialog.getClass().getSuperclass().getDeclaredField("mShowing");
                     field.setAccessible(true);//设置该属性可以访问
                 } catch (Exception ex) {

                 }

                 String inputValue = String.valueOf(mEdit.getText());
                 if (inputValue == null || "".equals(inputValue)) {
                     try {
                         //设置dialog不可关闭
                         field.set(dialog, false);
                         dialog.dismiss();
                     } catch (Exception ex) {
                     }
                 } else {

                    //
                    //做自己的事
                    //
                     try {
                         //关闭
                         field.set(dialog, true);
                         dialog.dismiss();
                     } catch (Exception ex) {
                     }
                 }
             }
         });
 builder.setNegativeButton("取消",
         new DialogInterface.OnClickListener() {
             @Override
             public void onClick(DialogInterface dialog, int id) {

                 Field field = null;

                 try {
                     //通过反射获取dialog中的私有属性mShowing
                     field = dialog.getClass().getSuperclass().getDeclaredField("mShowing");
                     field.setAccessible(true);//设置该属性可以访问
                 } catch (Exception ex) {
                 }

                 try {
                     field.set(dialog, true);
                     dialog.dismiss();
                 } catch (Exception ex) {
                 }

             }
         });

 builder.create();