最近项目中多次出现因为数组越界导致的app crash，因为总有人对数据进行读取、插入、删除和替换的过程中出现数组越界的情况。
- 读取：index超出array的索引范围
- 插入：index大于count、插入的object为nil或者Null
- 删除：index超出array的索引范围
- 替换：index超出array的索引范围、替换的object为nil或者Null
由于项目中存在有拦截器，在runtime中使用Aspects对UIViewController生命周期进行method swizzle。所以，首先想到的是是否可以对NSArray和NSMutableArray的这些方法进行替换，在替换的方法中对条件进行判断，来解决crash问题。
由于Objective-C方法调用是通过runtime进行objc_msgSend来决定具体调用哪个SEL，所以要想实现method swizzle，其实就是对SEL进行替换。对于Method Swizzling请参考这篇文章：http://nshipster.com/method-swizzling/
- 首先要对NSObject进行扩充，增加swizzleMethod方法，用于对系统方法进行替换
#import <Foundation/Foundation.h>
@interface NSObject (Swizzle)
/**
* 对系统方法进行替换
*
* @param originalSelector 被替换的方法
* @param swizzledSelector 实际使用的方法
* @param error 替换过程中出现的错误，如果没有错误则为nil
*
* @return 是否替换成功
*/
+ (BOOL)swizzleMethod:(SEL)originalSelector withMethod:(SEL)swizzledSelector error:(NSError **)error;
@end
#import "NSObject+Swizzle.h"
#import <objc/runtime.h>
@implementation NSObject (Swizzle)
@implementation NSObject (Swizzle)
+ (BOOL)swizzleMethod:(SEL)originalSelector withMethod:(SEL)swizzledSelector error:(NSError **)error {
Method originalMethod = class_getInstanceMethod(self, originalSelector);
if (!originalMethod) {
NSString *string = [NSString stringWithFormat:@"%@ 类没有找到 %@ 方法", NSStringFromClass([self class]), NSStringFromSelector(originalSelector)];
*error = [NSError errorWithDomain:@"NSCocoaErrorDomain" code:-1 userInfo:[NSDictionary dictionaryWithObject:string forKey:NSLocalizedDescriptionKey]];
return NO;
}
Method swizzledMethod = class_getInstanceMethod(self, swizzledSelector);
if (!swizzledMethod) {
NSString *string = [NSString stringWithFormat:@"%@ 类没有找到 %@ 方法", NSStringFromClass([self class]), NSStringFromSelector(swizzledSelector)];
*error = [NSError errorWithDomain:@"NSCocoaErrorDomain" code:-1 userInfo:[NSDictionary dictionaryWithObject:string forKey:NSLocalizedDescriptionKey]];
return NO;
}
if (class_addMethod([self class], originalSelector, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod))) {
class_replaceMethod([self class], swizzledSelector, method_getImplementation(originalMethod), method_getTypeEncoding(originalMethod));
} else {
method_exchangeImplementations(originalMethod, swizzledMethod);
}
return YES;
}- 书写拦截器，对NSArray和NSMutableArray的方法进行替换，主要替换的方法包括：objectAtIndex：，addObject:，insertObject:atIndex:，removeObjectAtIndex:和replaceObjectAtIndex:withObject:。
#import <Foundation/Foundation.h>
@interface YKIntercepter : NSObject
@end
#import "YKIntercepter.h"
#import <objc/runtime.h>
#import "NSObject+Swizzle.h"
#pragma mark Private Swizzle
#pragma mark - NSArray Method Swizzle
@interface NSArray (Swizzle)
- (id)yk_objectAtIndex:(NSUInteger)index;
@end
@implementation NSArray (Swizzle)
- (id)yk_objectAtIndex:(NSUInteger)index {
if (index < self.count) {
return [self yk_objectAtIndex:index];
}
return nil;
}
@end
#pragma mark - NSMutableArray Method Swizzle
@interface NSMutableArray (Swizzle)
- (id)yk_objectAtIndex:(NSUInteger)index;
- (void)yk_addObject:(id)anObject;
- (void)yk_insertObject:(id)anObject atIndex:(NSUInteger)index;
- (void)yk_removeObjectAtIndex:(NSUInteger)index;
- (void)yk_replaceObjectAtIndex:(NSUInteger)index withObject:(id)anObject;
@end
@implementation NSMutableArray (Swizzle)
- (id)yk_objectAtIndex:(NSUInteger)index {
if (index < self.count) {
return [self yk_objectAtIndex:index];
}
return nil;
}
- (void)yk_addObject:(id)anObject {
if (anObject != nil && [anObject isKindOfClass:[NSNull class]] == NO) {
[self yk_addObject:anObject];
}
}
- (void)yk_insertObject:(id)anObject atIndex:(NSUInteger)index {
if (index <= self.count && anObject != nil && [anObject isKindOfClass:[NSNull class]] == NO) {
[self yk_insertObject:anObject atIndex:index];
}
}
- (void)yk_removeObjectAtIndex:(NSUInteger)index {
if (index < self.count) {
[self yk_removeObjectAtIndex:index];
}
}
- (void)yk_replaceObjectAtIndex:(NSUInteger)index withObject:(id)anObject {
if (index < self.count && anObject != nil && [anObject isKindOfClass:[NSNull class]] == NO) {
[self yk_replaceObjectAtIndex:index withObject:anObject];
}
}
@end
#pragma mark YKIntercepter
#pragma mark - Implementation YKIntercepter
@implementation YKIntercepter
+ (void)load {
[super load];
[YKIntercepter sharedInstance];
}
+ (instancetype)sharedInstance {
static dispatch_once_t onceToken;
static YKIntercepter *sharedInstance;
dispatch_once(&onceToken, ^{
sharedInstance = [[YKIntercepter alloc] init];
});
return sharedInstance;
}
- (instancetype)init {
self = [super init];
if (self) {
//替换NSArray方法
[objc_getClass("__NSArrayI") swizzleMethod:@selector(objectAtIndex:) withMethod:@selector(yk_objectAtIndex:) error:nil];
//替换NSMutableArray方法
[objc_getClass("__NSArrayM") swizzleMethod:@selector(objectAtIndex:) withMethod:@selector(yk_objectAtIndex:) error:nil];
[objc_getClass("__NSArrayM") swizzleMethod:@selector(addObject:) withMethod:@selector(yk_addObject:) error:nil];
[objc_getClass("__NSArrayM") swizzleMethod:@selector(insertObject:atIndex:) withMethod:@selector(yk_insertObject:atIndex:) error:nil];
[objc_getClass("__NSArrayM") swizzleMethod:@selector(removeObjectAtIndex:) withMethod:@selector(yk_removeObjectAtIndex:) error:nil];
[objc_getClass("__NSArrayM") swizzleMethod:@selector(replaceObjectAtIndex:withObject:) withMethod:@selector(yk_replaceObjectAtIndex:withObject:) error:nil];
}
return self;
}
@end对于YKIntercepter：
+(void)load方法：上方的文章中提到，所有类的该方法在Objective-C runtime中会自动被调用。大名鼎鼎的IQKeyboardManager之所以不用写一行代码就可以引入，其实用的也是这种方法。
dispatch_once_t：保证方法swizzling只被执行一次
yk开头方法：yk开头的方法为替换方法，方法内部调用yk开头的方法并不会形成递归，因为方法被替换后，调用yk开头的方法实际上执行的是系统的方法。
使用方法不需要做任何改变，还是直接使用系统方法，对现有代码0入侵。