电话号码中间插入空格

[textField addTarget:self action:@selector(textFieldEditing:) forControlEvents:UIControlEventEditingChanged];

static NSInteger _phoneLength = 0;

- (void)textFieldEditing:(UITextField *)textField {
    
    if (textField.text.length > _phoneLength) {
        if (textField.text.length == 4 || textField.text.length == 9 ) { 
            NSMutableString *str = [[NSMutableString alloc ] initWithString:textField.text];
            [str insertString:@" " atIndex:(textField.text.length - 1)];
            textField.text = str;
        }
        
        if (textField.text.length >= 13 ) { // 输入完成
            textField.text = [textField.text substringToIndex:13];
        }
        
        _phoneLength = textField.text.length;
        
    } else if (textField.text.length < _phoneLength) { // 删除
        if (textField.text.length == 4 || textField.text.length == 9) {
            textField.text = [textField.text substringToIndex:(textField.text.length - 1)];
        }
        
        _phoneLength = textField.text.length;
    }
}