如何使当点击AlertDialog中的按钮时，AlertDialog不被dismiss掉

//通过反射来实现 @Override protected Dialog onCreateDialog(int id) { final AlertDialog.Builder builder=new AlertDialog.Builder(this); if(id==1){ builder.setTitle("标题"); builder.setMessage("消息"); final EditText et = new EditText(this); et.setWidth(LayoutParams.FILL_PARENT); et.setPadding(5, 5 ,5, 5); et.setTextSize(18); et.setHeight(160); et.setGravity(Gravity.TOP); builder.setView(et); final AlertDialog ad = builder.create(); ad.setButton("确定", new DialogInterface.OnClickListener(){ @Override public void onClick(DialogInterface dialog, int which) { if(et.getText().toString().trim().length()==0){ try { Field field = ad.getClass().getSuperclass() .getDeclaredField("mShowing"); field.setAccessible(true); field.set(ad, false); } catch (Exception e) { e.printStackTrace(); } } }}); ad.setButton2("取消",new DialogInterface.OnClickListener(){ @Override public void onClick(DialogInterface dialog, int which) { try { Field field = ad.getClass().getSuperclass() .getDeclaredField("mShowing"); field.setAccessible(true); field.set(ad, true); } catch (Exception e) { e.printStackTrace(); } }}); return ad; } return super.onCreateDialog(id); }