Latest 1.0.5
Homepage https://github.com/wuwen1030/XTSafeCollection
License MIT
Platforms ios
Authors

XTSafeCollection

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背景

NSArray``NSMutableArray``NSDictionary``NSMutableDictionary是我们的在iOS开发中非常常用的类。当然,在享受这些类的便利的同时,它们也给我们带来一些困扰。粗心我们可能会调用addObject传入一个nil, 也有可能是会objectAtIndex传入一个越界的index。尤其是在数据基本依赖于服务端返回的的情况,这种crash大幅增加。最近项目上经常出现NSDictionarysetObject:forKey:nil object的崩溃。

解决方案

函数包装

我们希望能够用一个统一的方法解决粗心的程序员可能传入的nil object。我们最先想到的想法是对这些函数进行一个包装,比如objectAtIndex,我们写一个如下的函数

- (id)safeObjectAtIndex:(NSUInteger)index
{   
    if (index >= self.count)
    {
        return nil;
    }
    return [self objectAtIndex:index];
}

以后所有调用objectAtIndex的地方统统替换为safeObjectAtIndex
不过,这显然不是我想要的,我不希望改变现有的调用方式,大家可能是通过[]objectAtIndex(不推荐)的方式获取数组元素,如果要做替换的话改动势必非常大,而且不便于以后的移植。我们希望代码调用objectAtIndex的时候,能够被我们先捕获到,进行处理之后再调用Cocoa的这个方法。Objective-C作为一门动态语言,有强大的动态加载的能力,提供了Method swizzling实现这样的功能。现在,黑魔法起飞。

Method swizzling

关于Method swizzling的具体实现,不打算多说,这里谈一下我遇到的问题。最初在做Method swizzling的时候,我尝试去替换NSArratobjectAtIndex:,但我始终没有办法替换掉这个方法。后来,搞了半天才发现,我们使用的NSAarray或者NSMutableArray并不是我们所看到样子,它们是class clusterobjectAtIndex:并不是他们的方法,而是他们背后的concrete class: __NSArrayI __NSArrayM的方法。解决了这个问题,剩下的就很简单了。

使用

直接把XTSafeCollection.h``XTSafeCollection.m拖入工程,NSArray``NSMutableArray``NSDictionary``NSMutableDictionary这些类的API以前是怎么调用的,还怎么写,完全不用修改。Demo里,我全部以传统的会引起crash的方式调用代码,以下是我的Demo的代码和输出

NSArray *array = @[@"a", @"b"];
NSMutableArray *mutableArray = [@[@"aa", @"bb"] mutableCopy];

// Object at index
NSLog(@"%@", array[10]);
NSLog(@"%@", mutableArray[100]);

// add object
[mutableArray addObject:nil];

// Insert object
[mutableArray insertObject:nil atIndex:0];
[mutableArray insertObject:@"cc" atIndex:10];

// Replace object
[mutableArray replaceObjectAtIndex:0 withObject:nil];
[mutableArray replaceObjectAtIndex:10 withObject:@"cc"];

// Dictionary
NSMutableDictionary *mutableDictionary = [NSMutableDictionary dictionary];
mutableDictionary[nil] = @"1";
mutableDictionary[@"1"] = nil;
2015-08-25 18:10:23.932 XTSafeCollection[29067:443479] [__NSArrayI objectAtIndex:] index {10} beyond bounds [0...1]
2015-08-25 18:10:23.933 XTSafeCollection[29067:443479] (null)
2015-08-25 18:10:23.933 XTSafeCollection[29067:443479] [__NSArrayM objectAtIndex:] index {100} beyond bounds [0...1]
2015-08-25 18:10:23.933 XTSafeCollection[29067:443479] (null)
2015-08-25 18:10:23.934 XTSafeCollection[29067:443479] [__NSArrayM addObject:], NIL object.
2015-08-25 18:10:23.934 XTSafeCollection[29067:443479] [__NSArrayM insertObject:atIndex:] NIL object.
2015-08-25 18:10:23.934 XTSafeCollection[29067:443479] [__NSArrayM insertObject:atIndex:] index {10} beyond bounds [0...1].
2015-08-25 18:10:23.934 XTSafeCollection[29067:443479] [__NSArrayM replaceObjectAtIndex:withObject:] NIL object.
2015-08-25 18:10:23.934 XTSafeCollection[29067:443479] [__NSArrayM replaceObjectAtIndex:withObject:] index {10} beyond bounds [0...1].
2015-08-25 18:10:23.934 XTSafeCollection[29067:443479] [__NSDictionaryM setObject:forKey:] NIL key.
2015-08-25 18:10:23.934 XTSafeCollection[29067:443479] [__NSDictionaryM setObject:forKey:] NIL object.

版本:

  • 1.0.0
NSArray:
- (id)objectAtIndex:(NSUInteger)index;

NSMutableArray:
- (id)objectAtIndex:(NSUInteger)index;
- (void)insertObject:(id)anObject atIndex:(NSUInteger)index;
- (void)addObject:(id)object;
- (void)replaceObjectAtIndex:(NSUInteger)index withObject:(id)anObject;

NSMutableDictionary:
- (void)setObject:(id)anObject forKey:(id <NSCopying>)aKey;
  • 1.0.2
NSArray:
+ (instancetype)arrayWithObjects:(const id [])objects count:(NSUInteger)cnt; ( @[] )

NSDictionary:
+ (instancetype)dictionaryWithObjects:(const id [])objects forKeys:(const id <NSCopying> [])keys count:(NSUInteger)cnt; ( @{} )

安装

pod "XTSafeCollection"

TODO

兼容更多的crash情况

Known Issues

替换NSMuatbelArrayobjectAtIndex:引起键盘展示状态态切换后台的崩溃,抛出

*** -[UIKeyboardLayoutStar release]: message sent to deallocated instance 0x7f883beac9c0

在这里
http://huang.sh/2015/02/%E4%B8%80%E4%B8%AA%E5%A5%87%E6%80%AA%E7%9A%84crash-uikeyboardlayoutstar-release/找到了解决方法
issue image

Latest podspec

{
    "name": "XTSafeCollection",
    "version": "1.0.5",
    "summary": "An elegant solution to common crashes of NSArray, NSMutableArray and NSMutableDictionary.",
    "description": "In Cocoa development, we often meet crashes like the follow:n1. `[NSArray objectAtIndex:]` when index exceeds array bounds.n2. `[NSMutableArray addObject]` when we attempt to add an nil Object.n...nnXTSafeCollection provide a way to avoid these crashes. Just add the `XTSafeCollection.h`, `XTSafeCollection.m` to you project,nYou event don't need to modify you codes, call the methods as what they are.nnMore: https://github.com/wuwen1030/XTSafeCollection.",
    "homepage": "https://github.com/wuwen1030/XTSafeCollection",
    "license": {
        "type": "MIT"
    },
    "authors": {
        "wuwen": "[email protected]"
    },
    "platforms": {
        "ios": null
    },
    "source": {
        "git": "https://github.com/wuwen1030/XTSafeCollection.git",
        "tag": "1.0.5"
    },
    "source_files": "XTSafeCollection/XTSafeCollection/*.{h,m}",
    "requires_arc": false
}

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