UITextField限制漢字數量最正確的姿勢,解決iOS7下substringToIndex方法導致的崩潰

今天在寫一個限制UITextField漢字數量的需求,原以為非常簡單的一個需求,在實際開發中遇到了很多問題.

首先,漢字的輸入時的聯想詞在輸入到TextFiled時,並不會走

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string;

這導致了在這裡進行長度限制的代碼都會失效.此路不通.

經過查找資料,得知可以用註冊UITextFieldTextDidChangeNotification通知來監測TextField的文字的變化

[[NSNotificationCenter defaultCenter]addObserver:self selector:@selector(textFiledEditChanged:) 
          name:@"UITextFieldTextDidChangeNotification" object:myTextField];

在textFiledEditChanged:方法中

- (void)textDidChanged:(NSNotification *)notification{
    
    NSInteger maxLength = 6;
    UITextField *textField = (UITextField *)notification.object;

    if (textField.text.length > maxLength)
    {
        textField.text = [textField.text substringToIndex:maxLength];
    }
}

　　這種方法看起來沒什麼問題,然而實測在iOS7下輸入漢字時,一旦長度到達最大長度,再進行輸入(此時輸入狀態還是拼音)就會立即崩潰.

*** Terminating app due to uncaught exception 'NSRangeException', reason: 'NSMutableRLEArray replaceObjectsInRange:withObject:length:: Out of bounds'

該問題在iOS8以上的系統中不會出現,可能是蘋果修複了該BUG.

再次查找資料,找到這篇博客http://www.jianshu.com/p/2d1c06f2dfa4

這篇博客解決了UItextFiled在截取字元串時,如果對emoji進行截取會變亂碼的問題(原因是emoji實際上占了3個長度).

UITextField *textField = (UITextField *)obj.object;
    NSString *toBeString = textField.text;

    //獲取高亮部分
    UITextRange *selectedRange = [textField markedTextRange];
    UITextPosition *position = [textField positionFromPosition:selectedRange.start offset:0];

    // 沒有高亮選擇的字，則對已輸入的文字進行字數統計和限制
    if (!position)
    {
        if (toBeString.length > MAX_STARWORDS_LENGTH)
        {
            NSRange rangeIndex = [toBeString rangeOfComposedCharacterSequenceAtIndex:MAX_STARWORDS_LENGTH];
            if (rangeIndex.length == 1)
            {
                textField.text = [toBeString substringToIndex:MAX_STARWORDS_LENGTH];
            }
            else
            {
                NSRange rangeRange = [toBeString rangeOfComposedCharacterSequencesForRange:NSMakeRange(0, MAX_STARWORDS_LENGTH)];
                textField.text = [toBeString substringWithRange:rangeRange];
            }
        }
    }

測試後發現,這個方法在iOS8以上的系統運行良好,但是在iOS7下居然完全失效了.

原因是在iOS7下,position對象總是不為nil,導致走不進處理長度的代碼.

研究後發現在需要增加一個判斷條件,

改進後的代碼:

UITextField *textField = (UITextField *)obj.object;
    NSString *toBeString = textField.text;

    //獲取高亮部分
    UITextRange *selectedRange = [textField markedTextRange];
    UITextPosition *position = [textField positionFromPosition:selectedRange.start offset:0];

    // 沒有高亮選擇的字，則對已輸入的文字進行字數統計和限制
    if (!position || !selectedRange)
    {
        if (toBeString.length > MAX_STARWORDS_LENGTH)
        {
            NSRange rangeIndex = [toBeString rangeOfComposedCharacterSequenceAtIndex:MAX_STARWORDS_LENGTH];
            if (rangeIndex.length == 1)
            {
                textField.text = [toBeString substringToIndex:MAX_STARWORDS_LENGTH];
            }
            else
            {
                NSRange rangeRange = [toBeString rangeOfComposedCharacterSequencesForRange:NSMakeRange(0, MAX_STARWORDS_LENGTH)];
                textField.text = [toBeString substringWithRange:rangeRange];
            }
        }
    }

再次測試後沒有發現崩潰問題了.