UITextField的placeholder的字体颜色和大小
[_nameText setValue: [UIColor lightGrayColor] forKeyPath:@"_placeholderLabel.textColor"];
[_nameText setValue:[UIFont boldSystemFontOfSize:13] forKeyPath:@"_placeholderLabel.font"];
[_nameText setValue: [UIColor lightGrayColor] forKeyPath:@"_placeholderLabel.textColor"];
[_nameText setValue:[UIFont boldSystemFontOfSize:13] forKeyPath:@"_placeholderLabel.font"];