iOS 修改textField的placeholder的字体颜色、大小

1.
textField.placeholder =
@"用户名";
[textField setValue:[UIColor redColor] forKeyPath:@"_placeholderLabel.textColor"];
[textField setValue:[UIFont boldSystemFontOfSize:16] forKeyPath:@"_placeholderLabel.font"];
2.
UIColor *color = [UIColor whiteColor];
_userName.attributedPlaceholder = [[NSAttributedString alloc] initWithString:@"用户名"
attributes:@{NSForegroundColorAttributeName: color}];