修改UITextField的佔位符的顏色

    

    注意:必須先設置placeholder

    self.valueTextField.placeholder = model.title;

    [self.valueTextField setValue:DefaultLineViewColor forKeyPath:@"_placeholderLabel.textColor"];

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