修改textField的placeholder的字体颜色、大小[

textField.placeholder = @"请输入验证码";

[textField setValue:[UIColor blueColor] forKeyPath:@"_placeholderLabel.textColor"];

[textField setValue:[UIFont boldSystemFontOfSize:14] forKeyPath:@"_placeholderLabel.font"];

_telTextField.contentVerticalAlignment = UIControlContentVerticalAlignmentCenter;;