iOS 數組越界 Crash處理經驗

我們先來看看有可能會出現的數組越界Crash的地方；

 

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
    WelfareItem *item = [_datasourceArray objectAtIndex:indexPath.row];//有可能會越界，你在下拉刷新時會用[_datasourceArray removeAllObjects]，這時你又點了某個cell就會Crash
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    WelfareItem *item = _datasourceArray[indexPath.row];//有可能會越界，兩個地方用了[tableView reloadData]；后一個有[_datasourceArray removeAllObjects]；前一個還沒有執行完，就會Crash
}

上面代碼是有可能會越界的；出現Crash也不好復現，發出去的App總是能收到幾條Crash；解決這個問題也很簡單代碼如下：

 

 

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
    WelfareItem *item = nil;
    if (indexPath.row < [_datasourceArray count]) {//無論你武功有多高，有時也會忘記加
        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];
    }
}

問題又來了，無論你武功有多高，有時也會忘記加；所以我們要想一招制敵辦法；我是想到了用Runtime把objectAtIndex方法替換一下；代碼如下：

 

 

/*!
 @category 
 @abstract NSObject的Category
 */
@interface NSObject (Util)

/*!
@method swizzleMethod:withMethod:error:
@abstract 對實例方法進行替換
@param oldSelector 想要替換的方法
@param newSelector 實際替換為的方法
@param error 替換過程中出現的錯誤，如果沒有錯誤為nil
*/
+ (BOOL)swizzleMethod:(SEL)originalSelector withMethod:(SEL)swizzledSelector error:(NSError **)error;

@end


#import "NSObject+Util.h"
#import 

@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:@" %@ 類沒有找到 %@ 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:@" %@ 類沒有找到 %@ 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;//越界返回為nil
}

@end

有了上面代碼我們用 [_datasourceArray objectAtIndex:indexPath.row] 就不會發生越界Crash了；越界
了會返回nil；看來是一個比較不錯的解決方案；把app發出去吧，結果我們Crash比之前高了好幾倍（越界的Crash沒有了，出新的Crash了）；Crash如下

 

 

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

都是這個Crash，出現在iOS7以上（含iOS7），關鍵還沒有用戶反饋有問題，Crash高了幾倍沒有一個用戶反饋這種情況還是少見的，大家測試還復現不了；測試了一周終於復現了一樣的Crash；是這樣出現的，替換了objectAtIndex方法有輸入的地方出來了軟鍵盤按手機Home鍵就Crash了；此法不行只，只能另尋他策了。后來我們就給數組新增擴展方法代碼如下

 

@interface NSArray (SHYUtil)

/*!
 @method objectAtIndexCheck:
 @abstract 檢查是否越界和NSNull如果是返回nil
 @result 返回對象
 */
- (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

把之前的代碼 WelfareItem *item = [_datasourceArray objectAtIndex:indexPath.row] 改為 WelfareItem *item = [_datasourceArray objectAtIndexCheck:indexPath.row] 就可以了。這樣就可以徹底解決數組越界 -[__NSArrayI objectAtIndex:]: index 100 beyond bounds [0 .. 1]' 錯誤了