UITextField set placeholderColor and UITextField set clearButton Image

　　self.usernameTextField.tintColor = [UIColor whiteColor];
    [self.usernameTextField setValue:UIColorFromRGBA(0xffffff, .6f) forKeyPath:@"_placeholderLabel.textColor"];
    self.passwordTextField.tintColor = [UIColor whiteColor];
    [self.passwordTextField setValue:UIColorFromRGBA(0xffffff, .6f) forKeyPath:@"_placeholderLabel.textColor"];
    UIButton *pwdClearButton = [self.passwordTextField valueForKey:@"_clearButton"];
    [pwdClearButton setImage:[UIImage imageNamed:@"login_icon_clear"] forState:UIControlStateNormal];
    UIButton *userNameClearButton = [self.usernameTextField valueForKey:@"_clearButton"];
    [userNameClearButton setImage:[UIImage imageNamed:@"login_icon_clear"] forState:UIControlStateNormal];