1、一般情况下，处理textFiled的字符数都会用到textField的代理方法
- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string;
在方法中对字符数进行控制，但是此方法的有一定的问题。现在推出一种新的自定义的机制，自定义textField控件，为其增加一个控制输入长度的属性，如下
.h文件
#import@interface PKTextField : UITextField@property (nonatomic,assign)NSInteger allowInputLength;@end
.m 文件
#import "PKTextField.h"@implementation PKTextField- (instancetype)init{ self = [super init]; if (self) { self.allowInputLength = CGFLOAT_MAX; [self addTarget:self action:@selector(textFieldEditChanged) forControlEvents:UIControlEventEditingChanged]; } return self;}- (instancetype)initWithFrame:(CGRect)frame{ self = [super initWithFrame:frame]; self.allowInputLength = CGFLOAT_MAX; [self addTarget:self action:@selector(textFieldEditChanged) forControlEvents:UIControlEventEditingChanged]; return self;}-(void)layoutSubviews{ [super layoutSubviews]; self.clipsToBounds = YES; self.backgroundColor = [UIColor whiteColor]; self.layer.cornerRadius = 2.5; self.layer.borderWidth = 0.5; self.borderStyle = UITextBorderStyleNone;}-(void)setEnabled:(BOOL)enabled{ [super setEnabled:enabled]; if (enabled == YES) { self.layer.borderColor = [UIColor colorFromHexRGB:@"999999" alpha:1.0].CGColor; CGRect frame = self.frame; frame.size.width = 5.0; UIView *leftview = [[UIView alloc] initWithFrame:frame]; self.leftViewMode = UITextFieldViewModeAlways; self.leftView = leftview; CGRect rightFrame = CGRectMake(0,0,5, self.bounds.size.height); UIView * rightView = [[UIView alloc] initWithFrame:rightFrame]; self.rightViewMode = UITextFieldViewModeAlways; self.rightView = rightView; }else{ self.layer.borderColor = [UIColor clearColor].CGColor; self.leftView = nil; self.rightView = nil; }}-(void)textFieldEditChanged{ UITextField *textField = self; NSString *toBeString = textField.text; //获取高亮部分 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 if (!position) { if (toBeString.length > self.allowInputLength) { NSRange rangeIndex = [toBeString rangeOfComposedCharacterSequenceAtIndex:self.allowInputLength]; if (rangeIndex.length == 1) { textField.text = [toBeString substringToIndex:self.allowInputLength]; } else { NSRange rangeRange = [toBeString rangeOfComposedCharacterSequencesForRange:NSMakeRange(0, self.allowInputLength)]; textField.text = [toBeString substringWithRange:rangeRange]; } } }}@end 使用示例：
PKTextField * titleTF = [[PKTextField alloc] initWithFrame:CGRectMake(leftPadding, 17, ScreenWidth - leftPadding - BtnHotWidth, 30)]; titleTF.textColor = [UIColor blackColor]; titleTF.enabled = NO; titleTF.text = @""; titleTF.font = [UIFont systemFontOfSize:23.0]; titleTF.allowInputLength = 10;