UITextField最大字符数和最大字节数的限制

UITextView,UITextfield中有很多坑，网上的方法也很多,但是用过之后暂时没有发现一个好用。这里我给大家几组测试用例可以一试，为啥不好用。

限制10个字节，输入2个Emoj之后是8个字节(一个Emoj是4个字节)，此时再输入一个中文，看看结果如何(中文的UTF8占3个字节)
限制5个字符,一个Emoj是2个字符,其他都是一个。此时输入两个Emoj，再输入中文，然后中文联想试试。

就目前的情况来说，看了很多资料，并没有一个通用的能限制字符数和字节数的封装。这里全面进行了总结，并进行了封装。欢迎大家下载。

一. 字符限制

1. 错误方法

常见的这种方法是错误的，会导致Emoj表情的截取问题

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
    if(range.length + range.location > textField.text.length)
    {
        return NO;
    }

    NSUInteger newLength = [textField.text length] + [string length] - range.length;
    return newLength <= 5;
}

这种限制方法会导致拼音下出现这种情况，且无法输入.无法输入满5个字符。在emoj表情也有问题

2. 推荐方法

使用rangeOfComposedCharacterSequencesForRange, 防止在range范围内整词被截断.因为中文的UTF8是3字节，Emoj是4个字节，且不能边输入边限制，否则中文联想的时候就无法继续输入。只能输入后在textfieldchange的时候进行截断。
综上所述，思路如下:

- (void)textFieldDidChange:(UITextField *)textField
{
    NSString *text = textField.text;
//    NSLog(@"text:%@",text);

    UITextRange *selectedRange = [textField markedTextRange];
    UITextPosition *position = [textField positionFromPosition:selectedRange.start offset:0];

    // 没有高亮选择的字，则对已输入的文字进行字数统计和限制,防止中文被截断

    if (!position){
        //---字符处理
        if (text.length > _maxLength){
            //中文和emoj表情存在问题，需要对此进行处理
            NSRange range;
            NSUInteger inputLength = 0;
            for(int i=0; i < text.length && inputLength <= _maxLength; i += range.length) {
                range = [textField.text rangeOfComposedCharacterSequenceAtIndex:i];
                inputLength += [text substringWithRange:range].length;
                if (inputLength > _maxLength) {
                    NSString* newText = [text substringWithRange:NSMakeRange(0, range.location)];
                    textField.text = newText;
                }
            }
        }
    }
}

二. 字节限制

1. 限制字节数

在UTF8中，英文和数字是1个字节,汉子是3个字节，emoji是3或者4个字节。这里的难度比上面更大，如果截取失败，极有可能出现乱码。这里我们的做法如下

- (void)textFieldDidChange:(UITextField *)textField
{
    NSString *text = textField.text;
//    NSLog(@"text:%@",text);

    UITextRange *selectedRange = [textField markedTextRange];
    UITextPosition *position = [textField positionFromPosition:selectedRange.start offset:0];

    // 没有高亮选择的字，则对已输入的文字进行字数统计和限制,防止中文被截断

    if (!position){
        //---字节处理
        //Limit
        NSUInteger textBytesLength = [textField.text lengthOfBytesUsingEncoding:NSUTF8StringEncoding];
        if (textBytesLength > _maxBytesLength) {
            NSRange range;
            NSUInteger byteLength = 0;
            for(int i=0; i < text.length && byteLength <= _maxBytesLength; i += range.length) {
                range = [textField.text rangeOfComposedCharacterSequenceAtIndex:i];
                byteLength += strlen([[text substringWithRange:range] UTF8String]);
                if (byteLength > _maxBytesLength) {
                    NSString* newText = [text substringWithRange:NSMakeRange(0, range.location)];
                    textField.text = newText;
                }
            }
        }
    }
    if (self.textFieldChange) {
        self.textFieldChange(self,textField.text);
    }
}

三. 放弃键盘

1. 能拿到uitextfield的时候用

- (BOOL)textFieldShouldReturn:(UITextField *)textField
{
    return [textField resignFirstResponder];
}

2. 点击view消失的时候用

1	[self.view endEditing:YES];

3. 难以获取的时候用

1	[[UIApplication sharedApplication] sendAction:@selector(resignFirstResponder) to:nil from:nil forEvent:nil];

或者

1	[[[UIApplication sharedApplication] keyWindow] endEditing:YES];

2.Tableview点击空白处或者滚动时消失

{
    UITapGestureRecognizer *singleTap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(fingerTapped:)];
    [self.view addGestureRecognizer:singleTap];
}

#pragma mark- 键盘消失
-(void)fingerTapped:(UITapGestureRecognizer *)gestureRecognizer{
    [self.view endEditing:YES];
}
-(void)scrollViewWillBeginDragging:(UIScrollView *)scrollView{
    [self.view endEditing:YES];
}

四. 正则表达式限制

请参考正则表达式语法表,这里我提供了两种表达式给大家参考，一个Int,一个无unsignedInt

-(BOOL) isTextFieldMatchWithRegularExpression:(NSString *)exporession{

    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"SELF MATCHES %@",exporession];
    return [predicate evaluateWithObject:self];
}
-(BOOL) isTextFieldIntValue{
    return [self isTextFieldMatchWithRegularExpression:@"[-]{0,1}[0-9]*"];
}
-(BOOL) isTextFieldUnsignedIntValue{
    return [self isTextFieldMatchWithRegularExpression:@"[0-9]+"];
}

五. UITextfield的键盘事件多次回调问题

1.键盘高度遮挡问题

一般出现遮挡的时候我们用以下代码,看看当前textfield是否在键盘下面，在的话算出键盘的顶端和textfield的底部的距离，然后做偏移动画

- (void)keyboardWillShow:(NSNotification *)notification {

    NSDictionary *userInfo = [notification userInfo];

    NSValue* aValue = [userInfo objectForKey:UIKeyboardFrameEndUserInfoKey];
    CGRect keyboardRect = [aValue CGRectValue];
    keyboardRect = [self.view convertRect:keyboardRect fromView:nil];

    CGFloat keyboardTop = keyboardRect.origin.y;

    CGFloat offset = self.normalTextField.frame.size.height + self.normalTextField.frame.origin.y - keyboardTop;

    NSValue *animationDurationValue = [userInfo objectForKey:UIKeyboardAnimationDurationUserInfoKey];
    NSTimeInterval animationDuration;
    [animationDurationValue getValue:&animationDuration];

    if(offset > 0){
        // Animate the resize of the text view's frame in sync with the keyboard's appearance.
        [UIView beginAnimations:nil context:NULL];
        [UIView setAnimationDuration:animationDuration];

        CGRect rect = CGRectMake(0.0f, -offset,self.view.frame.size.width,self.view.frame.size.height);
        self.view.frame = rect;
        [UIView commitAnimations];
    }
}

真机
如果使用了中文输入法，注册的keyboardWillShow会回调两次。第一次是键盘默认高度216，第二次则是加了keyboard的导航栏的高度。
模拟器
第一次弹出键盘没有问题

打印userinfo:

(lldb) po userInfo
{
    UIKeyboardAnimationCurveUserInfoKey = 7;
    UIKeyboardAnimationDurationUserInfoKey = "0.25";
    UIKeyboardBoundsUserInfoKey = "NSRect: {{0, 0}, {414, 226}}";
    UIKeyboardCenterBeginUserInfoKey = "NSPoint: {207, 849}";
    UIKeyboardCenterEndUserInfoKey = "NSPoint: {207, 623}";
    UIKeyboardFrameBeginUserInfoKey = "NSRect: {{0, 736}, {414, 226}}";
    UIKeyboardFrameEndUserInfoKey = "NSRect: {{0, 510}, {414, 226}}";
    UIKeyboardIsLocalUserInfoKey = 1;
}

此时我们去按123旁边的小圆球会出现如下的图：

打印userinfo:

(lldb) po userInfo
{
    UIKeyboardAnimationCurveUserInfoKey = 7;
    UIKeyboardAnimationDurationUserInfoKey = "0.25";
    UIKeyboardBoundsUserInfoKey = "NSRect: {{0, 0}, {414, 271}}";
    UIKeyboardCenterBeginUserInfoKey = "NSPoint: {207, 623}";
    UIKeyboardCenterEndUserInfoKey = "NSPoint: {207, 600.5}";
    UIKeyboardFrameBeginUserInfoKey = "NSRect: {{0, 510}, {414, 226}}";
    UIKeyboardFrameEndUserInfoKey = "NSRect: {{0, 465}, {414, 271}}";
    UIKeyboardIsLocalUserInfoKey = 1;
}

键盘被遮挡了。

总结:观察结果,发现了这个规律，打印一下时间,还有一个问题就是，中文键盘第一次启动的时候会回调两次。

1	keyboardRect = [self.view convertRect:keyboardRect fromView:nil];

所以去掉这句话即可

六. 使用封装的XXTextField

UITextView,UITextfield中如果有keyboard的时候，需要一个自动弹起事件，以及弹起之后的content的偏移对父view的处理。如果每个页面都实现一次会非常复杂。这里我们介绍一种自动化的处理机制。在此之前，先介绍一下文字处理框架.最后给大家推荐一下我写的XXTextField,大家也可以在此基础上自己添加一些正则表达式。使用方法很简单.欢迎加入QQ群：237305299 ，一起探讨iOS技术问题

1.解决uiview中的textfield 遮挡问题

_textfieldName.keyboardType = UIKeyboardTypeDefault;
_textfieldName.inputType = XXTextFieldTypeOnlyInt;
_textfieldName.maxLength = 5;
_textfieldPwd.inputType = XXTextFieldTypeForbidEmoj;

#import "XXKeyboardManager.h"
@interface XXCorrectVC ()<XXKeyboardManagerShowHiddenNotificationDelegate>
@end

@implementation XXCorrectVC

- (void)viewDidLoad {
    [super viewDidLoad];
    [[XXKeyboardManager sharedInstance] setDelegate:self];
    // Do any additional setup after loading the view from its nib.
}
#pragma mark- KeyBoardShow/Hidden
- (void)showKeyboardWithRect:(CGRect)keyboardRect
                withDuration:(CGFloat)animationDuration
{
    CGFloat offset = self.textFieldCorrect.frame.size.height + self.textFieldCorrect.frame.origin.y - keyboardRect.origin.y;
    if(offset < 0){
        return;
    }
    [UIView animateWithDuration:animationDuration
                          delay:0.f
                        options:UIViewAnimationOptionCurveEaseInOut animations:^{
        CGRect rect = CGRectMake(0.0f, -offset,self.view.frame.size.width,self.view.frame.size.height);
        self.view.frame = rect;
    } completion:^(BOOL finished) {

    }];
}

- (void)hiddenKeyboardWithRect:(CGRect)keyboardRect
                  withDuration:(CGFloat)animationDuration
{
    [UIView animateWithDuration:animationDuration
                          delay:0.f
                        options:UIViewAnimationOptionCurveEaseInOut animations:^{
        self.textFieldCorrect.frame = self.view.bounds;
    } completion:^(BOOL finished) {
    }];
}
@end

2.解决uitableview中键盘遮挡问题

/*
 * 键盘要显示的时候
 */
- (void)showKeyboardWithRect:(CGRect)keyboardRect
                withDuration:(CGFloat)animationDuration{

    CGSize kbSize = keyboardRect.size;

    UIEdgeInsets contentInsets = UIEdgeInsetsMake(0.0, 0.0, kbSize.height, 0.0);
    _baseTableView.contentInset = contentInsets;
    _baseTableView.scrollIndicatorInsets = contentInsets;

    // If active text field is hidden by keyboard, scroll it so it's visible
    // Your app might not need or want this behavior.
    CGRect aRect = self.view.frame;
    aRect.size.height -= kbSize.height;

    if (!CGRectContainsPoint(aRect, _activeCell.frame.origin) ) {
        [_baseTableView scrollRectToVisible:_activeCell.frame animated:YES];
    }http://www.90168.org/
}

/*
 * 键盘要消失的时候
 */
- (void)hiddenKeyboardWithRect:(CGRect)keyboardRect
                  withDuration:(CGFloat)animationDuration{
    _baseTableView.contentInset = UIEdgeInsetsZero;
    _baseTableView.scrollIndicatorInsets = UIEdgeInsetsZero;
}