我们先来看看有可能会出现的数组越界Crash的地方；
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- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
WelfareItem *item = [_datasourceArray objectAtIndex:indexPath.row];//有可能会越界，你在下拉刷新时会用[_datasourceArray removeAllObjects]，这时你又点了某个cell就会Crash
}- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { WelfareItem *item = _datasourceArray[indexPath.row];//有可能会越界，两个地方用了[tableView reloadData]；后一个有[_datasourceArray removeAllObjects]；前一个还没有执行完，就会Crash
} |
上面代码是有可能会越界的；出现Crash也不好复现，发出去的App总是能收到几条Crash；解决这个问题也很简单代码如下：
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- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
WelfareItem *item = nil;
if (indexPath.row < [_datasourceArray count]) {//无论你武功有多高，有时也会忘记加
item = [_datasourceArray objectAtIndex:indexPath.row];
}
}- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { WelfareItem *item = nil;
if (indexPath.row < [_datasourceArray count]) {
item = [_datasourceArray objectAtIndex:indexPath.row];
}
} |
问题又来了，无论你武功有多高，有时也会忘记加；所以我们要想一招制敌办法；我是想到了用Runtime把objectAtIndex方法替换一下；代码如下：
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/*! @category
@abstract NSObject的Category
*/
@interface NSObject (Util)
/*!@method swizzleMethod:withMethod:error:@abstract 对实例方法进行替换@param oldSelector 想要替换的方法@param newSelector 实际替换为的方法@param error 替换过程中出现的错误，如果没有错误为nil*/+ (BOOL)swizzleMethod:(SEL)originalSelector withMethod:(SEL)swizzledSelector error:(NSError **)error;@end#import "NSObject+Util.h"
#import <objc runtime.h="">
@implementation NSObject (Util)
+ (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, originalSelector, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod))) {
class_replaceMethod(self, swizzledSelector, method_getImplementation(originalMethod), method_getTypeEncoding(originalMethod));
}
else {
method_exchangeImplementations(originalMethod, swizzledMethod);
}
return YES;
}@end@implementation NSArray (ErrerManager)
+ (void)load
{ static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
@autoreleasepool
{
[objc_getClass("__NSArrayI") swizzleMethod:@selector(objectAtIndex:) withMethod:@selector(swizzleObjectAtIndex:) error:nil];
[objc_getClass("__NSArrayM") swizzleMethod:@selector(objectAtIndex:) withMethod:@selector(swizzleObjectAtIndex:) error:nil];
};
});
}- (id)swizzleObjectAtIndex:(NSUInteger)index{ if (index < self.count)
{
return [self swizzleObjectAtIndex:index];
}
NSLog(@"%@ 越界",self);
return nil;//越界返回为nil
}@end</objc>
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有了上面代码我们用 [_datasourceArray objectAtIndex:indexPath.row] 就不会发生越界Crash了；越界
了会返回nil；看来是一个比较不错的解决方案；把app发出去吧，结果我们Crash比之前高了好几倍（越界的Crash没有了，出新的Crash了）；Crash如下
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1 tbreader 0x002b93e9 tbreader + 2098153
2 libsystem_platform.dylib 0x33a66873 _sigtramp + 34
3 libsystem_blocks.dylib 0x33941ae1 _Block_release + 216
4 libobjc.A.dylib 0x333c11a9 + 404
5 CoreFoundation 0x25ba23a9 _CFAutoreleasePoolPop + 16
6 UIKit 0x2912317f + 42
7 CoreFoundation 0x25c565cd + 20
8 CoreFoundation 0x25c53c8b + 278
9 CoreFoundation 0x25c54093 + 914
10 CoreFoundation 0x25ba2621 CFRunLoopRunSpecific + 476
11 CoreFoundation 0x25ba2433 CFRunLoopRunInMode + 106
12 GraphicsServices 0x2cf0a0a9 GSEventRunModal + 136
13 UIKit 0x2918c809 UIApplicationMain + 1440
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都是这个Crash，出现在iOS7以上（含iOS7），关键还没有用户反馈有问题，Crash高了几倍没有一个用户反馈这种情况还是少见的，大家测试还复现不了；测试了一周终于复现了一样的Crash；是这样出现的，替换了objectAtIndex方法有输入的地方出来了软键盘按手机Home键就Crash了；此法不行只，只能另寻他策了。后来我们就给数组新增扩展方法代码如下
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@interface NSArray (SHYUtil)
/*! @method objectAtIndexCheck:
@abstract 检查是否越界和NSNull如果是返回nil
@result 返回对象
*/
- (id)objectAtIndexCheck:(NSUInteger)index;@end#import "NSArray+SHYUtil.h"
@implementation NSArray (SHYUtil)
- (id)objectAtIndexCheck:(NSUInteger)index{ if (index >= [self count]) {
return nil;
}
id value = [self objectAtIndex:index];
if (value == [NSNull null]) {
return nil;
}
return value;
}@end |
把之前的代码 WelfareItem *item = [_datasourceArray objectAtIndex:indexPath.row] 改为 WelfareItem *item = [_datasourceArray objectAtIndexCheck:indexPath.row] 就可以了。这样就可以彻底解决数组越界 -[__NSArrayI objectAtIndex:]: index 100 beyond bounds [0 .. 1]' 错误了