在textview iOS中属性字符串的末尾添加nsstring

我有一个类似“你好”的文本，它将是一个红色的属性字符串。然后在该属性字符串的末尾，我想附加一个nsstring“Who is you？”，但每当我附加一个nsstring时，整个字符串都会变成普通的nsstring，并且属性字符串的属性会被删除。我迄今为止的努力：

NSMutableAttributedString *attributeString = [[NSMutableAttributedString alloc] initWithString:@"Hello There"];
[attributeString addAttribute:NSForegroundColorAttributeName value:[UIColor redColor] range:NSMakeRange(0,[attributeString length])];

NSMutableAttributedString *previousAttrString = [[NSMutableAttributedString alloc] initWithString:messageTextView.text];

[previousAttrString insertAttributedString: attributeString atIndex:location];
messageTextView.attributedText = previousAttrString;
messageTextView.font = [UIFont fontWithName:@"Helvetica" size:15];

NSString *messageWithContact = [NSString stringWithFormat: @"%@ %@", messageTextView.text, @"Who are you?"];
messageTextView.text=messageWithContact;

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我做错了什么？请帮助我。

替换底线

NSString *messageWithContact = [NSString stringWithFormat: @"%@ %@", messageTextView.text, @"Who are you?"];
messageTextView.text=messageWithContact;

与

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编辑的第一行应该是：

NSMutableAttributedString*newString=[[NSMutableAttributedString alloc]initWithAttributedString:messageTextView.attributedText]
NSMutableAttributedString *newString = messageTextView.attibutedText;
[newString appendAttributedString: [[NSAttributedString alloc] initWithString: @"Who are you?"];
messageTextView.attibutedText = newString;