UITextView *userNameText = [[UITextField  alloc]init];
//新增使用者名稱文字框背景圖片
UIImageView *userImgView=[[UIImageView alloc] initWithFrame:userNameText.bounds];
userImgView.image=[UIImage imageNamed:@"使用者名稱、密碼輸入框.png"];
userImgView.contentMode = UIViewContentModeScaleToFill;
[userNameText  addSubview:userImgView];
//sendSubviewToBack 將該subview置於最底層
[userNameText sendSubviewToBack:userImgView];