在shouldChangeTextInRange期间防止删除前缀

我有一个UITextView有一个前缀包含一个4字符的空白string作为缩进。 如果我键入大量文本，然后按住退格button一秒钟左右，它会逐字逐句删除文本，但也会删除我的“分隔符空间”，从而导致我的UITextView卡住，无法使用打字了。

这是我正在谈论的问题：

 if (range.location <= 4 && textView == self.descriptionTextView) { #warning fast deletion causes this to be un-editable return NO; // makes sure no one can edit the first 4 chars } 

如何防止这种“快速删除”删除“分隔空间”呢？

Answer 1

为了保持你的前缀，我build议搞清楚如果你实际上改变给定范围内的字符会导致的string，然后只允许文本改变，如果前缀不保持原样; 例如，在你的具体情况下：

 - (BOOL)textView:(UITextView *)textView shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string { // Combine the new text with the old NSString *combinedText = [textView.text stringByReplacingCharactersInRange:range withString:string]; // If the user attempts to delete before the 4th // character, delete all but the first 4 characters if (combinedText.length < 4) { textView.text = @" "; // <-- or whatever the first 4 characters are return NO; } // Else if the user attempts to change any of the first // 4 characters, don't let them else if (![[textView.text substringToIndex:4] isEqualToString:[combinedText substringToIndex:4]]) { return NO; } return YES; } 

或者更一般地说，为了保持灵活性，您可以将前缀string存储为类实例variables，然后根据前缀variables可能存在的shouldChangeCharactersInRange:代码：

 - (BOOL)textView:(UITextView *)textView shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string { // Combine the new text with the old NSString *combinedText = [textView.text stringByReplacingCharactersInRange:range withString:string]; // If the user attempts to delete into the prefix // character, delete all but the prefix if (combinedText.length < self.prefixString.length) { textView.text = self.prefixString; return NO; } // Else if the user attempts to change any of the prefix, // don't let them else if (![self.prefixString isEqualToString:[combinedText substringToIndex:self.prefixString.length]]) { return NO; } return YES; }