iOS 數組越界 Crash處理經驗

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，你在下拉重新整理時會用[_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]；後一個有[_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也不好複現，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 對執行個體方法進行替換@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 + 20981532 libsystem_platform.dylib 0x33a66873 _sigtramp + 343 libsystem_blocks.dylib 0x33941ae1 _Block_release + 2164 libobjc.A.dylib 0x333c11a9 + 4045 CoreFoundation 0x25ba23a9 _CFAutoreleasePoolPop + 166 UIKit 0x2912317f + 427 CoreFoundation 0x25c565cd + 208 CoreFoundation 0x25c53c8b + 2789 CoreFoundation 0x25c54093 + 91410 CoreFoundation 0x25ba2621 CFRunLoopRunSpecific + 47611 CoreFoundation 0x25ba2433 CFRunLoopRunInMode + 10612 GraphicsServices 0x2cf0a0a9 GSEventRunModal + 13613 UIKit 0x2918c809 UIApplicationMain + 1440

都是這個Crash，出現在iOS7以上（含iOS7），關鍵還沒有使用者反饋有問題，Crash高了幾倍沒有一個使用者反饋這種情況還是少見的，大家測試還複現不了；測試了一周終於複現了一樣的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。後來我們就給數組新增擴充方法代碼如下

 

@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