设置 textField.placeholder的颜色和大小
textField.placeholder = @"请输入手机号码";
[textField setValue:[UIColor blue] forKeyPath:@"_placeholderLabel.textColor"];
[textField setValue:[UIFont systemFontOfSize:14] forKeyPath:@"_placeholderLabel.font"];
textField.placeholder = @"请输入手机号码";
[textField setValue:[UIColor blue] forKeyPath:@"_placeholderLabel.textColor"];
[textField setValue:[UIFont systemFontOfSize:14] forKeyPath:@"_placeholderLabel.font"];