修改UITextfield的Placeholder字体的颜色
//第一种 UIColor *color = [UIColor whiteColor]; _userName.attributedPlaceholder = [[NSAttributedString alloc] initWithString:@"用户名" attributes:@{NSForegroundColorAttributeName: color}]; //第二种 [_userName setValue:[UIColor whiteColor] forKeyPath:@"_placeholderLabel.textColor"];