首先创建一个UITextField的Category文件
<UITextField+DC.h>
#import <UIKit/UIKit.h>
IB_DESIGNABLE
@interface UITextField (DC)
/**
设置最大长度
*/
@property (nonatomic, assign) IBInspectable NSUInteger maxLength;
@end
<UITextField+DC.m>
#import "UITextField+DC.h"
#import <objc/runtime.h>
static char kMaxLength;
@interface UItextFieldMaxLengthObserver : NSObject
@end
@implementation UItextFieldMaxLengthObserver
- (void)textChange:(UITextField *)textField {
NSString *destText = textField.text;
NSUInteger maxLength = textField.maxLength;
// 对中文的特殊处理，shouldChangeCharactersInRangeWithReplacementString 并不响应中文输入法的选择事件
// 如拼音输入时，拼音字母处于选中状态，此时不判断是否超长
UITextRange *selectedRange = [textField markedTextRange];
if (!selectedRange || !selectedRange.start) {
if (destText.length > maxLength) {
textField.text = [destText substringToIndex:maxLength];
}
}
}
@end
static UItextFieldMaxLengthObserver *observer;
@implementation UITextField (DC)
@dynamic maxLength;
+ (void)load {
observer = [[UItextFieldMaxLengthObserver alloc] init];
}
- (void)setMaxLength:(NSUInteger)maxLength {
objc_setAssociatedObject(self, &kMaxLength, @(maxLength), OBJC_ASSOCIATION_RETAIN_NONATOMIC);
if (maxLength) {
[self addTarget:observer
action:@selector(textChange:)
forControlEvents:UIControlEventEditingChanged];
}
}
-(NSUInteger)maxLength {
NSNumber *number = objc_getAssociatedObject(self, &kMaxLength);
return [number integerValue];
}
@end
