iOS 数组越界 Crash处理经验

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

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

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