[iOS]UITextField和UITextView限制输入字符数量方面

[iOS]UITextField和UITextView限制输入字符数量方面

demo:http://download.csdn.net/download/u012881779/9960401

UITextField和UITextView限制输入字符数量，以前一直是在对应的代理方法（shouldChangeCharactersInRange:）中操作。但这样操作存在一个bug（如图），在将要超过限制时输入一串比较长的字符串，选择这段字符串时就会提示“超过限制”，实际上这时是还能继续输入几个字符的。

本文主要就是为了解决这类bug。

#import "DMViewController.h"

// 限制输入字符数
#define YH_LIMITWORD 20
#define YH_LIMITTEXTWORD 60

@interface DMViewController () <UITextViewDelegate>
@property (weak, nonatomic) IBOutlet UITextField *titleText;
@property (weak, nonatomic) IBOutlet UITextView *contentTextView;
@property (strong, nonatomic) NSString *defaultText;

@end

@implementation DMViewController

- (void)dealloc {
    [[NSNotificationCenter defaultCenter] removeObserver:self];
}

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
    [self.view endEditing:YES];
}

- (void)viewDidLoad {
    [super viewDidLoad];
    _defaultText = @"限制输入60个字符";
    // 方式一
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textDidChangeAction:) name:@"UITextFieldTextDidChangeNotification" object:_titleText];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textDidChangeAction:) name:@"UITextViewTextDidChangeNotification" object:_contentTextView];
    // 方式二（UITextField可以在UIControlEventEditingChanged事件的响应textDidChangeAction方法）
    // [_titleText addTarget:self action:@selector(textDidChangeAction:) forControlEvents:UIControlEventEditingChanged];
    // 方式三（UITextView可以在代理方法textViewDidChange中调用textDidChangeAction方法）
}

#pragma mark - Notification
- (void)textDidChangeAction:(NSNotification *)sender {
    UITextField *textObject;
    if ([[sender class] isSubclassOfClass:[NSNotification class]]) {
        textObject = sender.object;
    } else {
        textObject = (id)sender;
    }
    NSInteger limitNum;
    if ([[textObject class] isSubclassOfClass:[UITextField class]]) {
        limitNum = YH_LIMITWORD;
    } else {
        limitNum = YH_LIMITTEXTWORD;
    }
    
    NSString *toBeString = textObject.text;
    // 获取高亮部分
    UITextRange *selectedRange = [textObject markedTextRange];
    UITextPosition *position = [textObject 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
    if (!position) {
        if (toBeString.length > limitNum) {
            NSRange rangeIndex = [toBeString rangeOfComposedCharacterSequenceAtIndex:limitNum];
            if (rangeIndex.length == 1) {
                textObject.text = [toBeString substringToIndex:limitNum];
            } else {
                NSRange rangeRange = [toBeString rangeOfComposedCharacterSequencesForRange:NSMakeRange(0, limitNum)];
                textObject.text = [toBeString substringWithRange:rangeRange];
            }
        }
    }
}

#pragma mark - UITextViewDelegate
- (BOOL)textViewShouldBeginEditing:(UITextView *)textView {
    NSString *text = textView.text;
    if ([text containsString:_defaultText]) {
        text = [text stringByReplacingOccurrencesOfString:_defaultText withString:@""];
    }
    textView.text = text;
    return YES;
}

- (void)textViewDidEndEditing:(UITextView *)textView {
    if ([textView.text isEqualToString:@""]) {
        textView.text = _defaultText;
    }
}

- (void)textViewDidChange:(UITextView *)textView {
    //[self textDidChangeAction:(id)textView];
}

@end

示意图：