_textField.placeholder = @"我是占位符"; // 系统设置占位符这句必须要在前面,这样才能通过keypath 获取placeholderLabel
UILabel *labe = (UILabel *)[_textField valueForKeyPath:@"_placeholderLabel"];
labe.textColor = [UIColor greenColor];
labe.textAlignment = NSTextAlignmentCenter;
UILabel *labe = (UILabel *)[_textField valueForKeyPath:@"_placeholderLabel"];
labe.textColor = [UIColor greenColor];
labe.textAlignment = NSTextAlignmentCenter;