iOS开发——高级篇——iOS如何彻底避免数组越界

我们先来看看有可能会出现的数组越界Crash的地方；

 

?

1 2 3 4 5 6 7

- ( 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：

 

 

?

1 2 3 4 5 6 7 8 9 10 11 12 13

- ( 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：

 

 

?

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77

/*!   @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>

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

 

 

?

1 2 3 4 5 6 7 8 9 10 11 12 13

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

 

?

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

@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

转载于:https://www.cnblogs.com/chglog/p/5322946.html