需求： UITextFiled 限制只能输入4个中文；一起一切字符，禁止输入；
解决方案：添加监听，在监听中，过滤字符；
1，声明变量：
@property (nonatomic, strong) UITextField *textField;
2，添加监听：
[[NSNotificationCenter defaultCenter]addObserver:self selector:@selector(textFiledEditChanged:)
name:UITextFieldTextDidChangeNotification object:self.textField];
3，在监听中，过滤非中文字符，并且限制中文字符长度；
- (BOOL)textFieldShouldReturn:(UITextField *)textField{
[textField resignFirstResponder];
//过滤非汉字字符
textField.text = [self filterCharactor:textField.text withRegex:@"[^\u4e00-\u9fa5]"];
if (textField.text.length >= 4) {
textField.text = [textField.text substringToIndex:4];
}
return NO;
}
- (void)textFiledEditChanged:(id)notification{
UITextRange *selectedRange = self.textField.markedTextRange;
UITextPosition *position = [self.textField positionFromPosition:selectedRange.start offset:0];
if (!position) { //// 没有高亮选择的字
//过滤非汉字字符
self.textField.text = [self filterCharactor:self.textField.text withRegex:@"[^\u4e00-\u9fa5]"];
if (self.textField.text.length >= 4) {
self.textField.text = [self.textField.text substringToIndex:4];
}
}else { //有高亮文字
//do nothing
}
}
//根据正则，过滤特殊字符
- (NSString *)filterCharactor:(NSString *)string withRegex:(NSString *)regexStr{
NSString *searchText = string;
NSError *error = NULL;
NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:regexStr options:NSRegularExpressionCaseInsensitive error:&error];
NSString *result = [regex stringByReplacingMatchesInString:searchText options:NSMatchingReportCompletion range:NSMakeRange(0, searchText.length) withTemplate:@""];
return result;
}
4，移除监听：
- (void)dealloc{
[[NSNotificationCenter defaultCenter] removeObserver:self];
}
5，Over；
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