首先參考一下自己之前寫的《method swizzing》這篇，特別是對類簇的methodSwizzing。

Container 類型的crash 指的是容器類的crash，常見的有NSArray／NSMutableArray／NSDictionary／NSMutableDictionary／NSCache的crash。 一些常見的越界、插入nil等錯誤操作均會導(dǎo)致此類crash發(fā)生。 由于產(chǎn)生的原因比較簡單，就不展開來描述了。

該類crash雖然比較容易排查，但是其在app crash概率總比還是挺高，所以有必要對其進(jìn)行防護(hù)。另外NSString也有類似的crash防護(hù)措施，在此篇中一并舉例說明。

一、Container類型和NSString類型常見crash

(1) [aMutableDictionary setObject:nil forKey:]; object can not be nil.

(2) [aString hasSuffix:nil]; nil argument crash.

[aString hasPrefix:nil]; nil argument crash.

(3) aString = [NSMutableString stringWithString:nil];nil argument crash.

(4) aString = [[NSString alloc] initWithString:nil]; nil argument crash.

(5) aURL = [NSURL fileURLWithPath:nil]; nil argument crash.

(6) NSArray 數(shù)組越界 crash。

二、使用method swizzing對常見crash防護(hù)舉例

這里對NSString、NSMutableDictionary和NSArray常見的幾個crash舉例如下：

（1）對NSString的hasSuffix：和hasPrefix:進(jìn)行預(yù)防：

#import "NSString+CrashGurad.h"
#import <objc/runtime.h>

@implementation NSString (CrashGurad)

#pragma mark Class Method

+(void)load {
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        [[self class] swizzedMethod:@selector(hasSuffix:) withMethod:@selector(crashGuard_hasSuffix:)];
        [[self class] swizzedMethod:@selector(hasPrefix:) withMethod:@selector(crashGuard_hasPrefix:)];
    });
}

+(void)swizzedMethod:(SEL)originalSelector withMethod:(SEL )swizzledSelector {
    
    Method fromMethod = class_getInstanceMethod(objc_getClass("__NSCFConstantString"), originalSelector);
    Method toMethod = class_getInstanceMethod(objc_getClass("__NSCFConstantString"), swizzledSelector);
    method_exchangeImplementations(fromMethod, toMethod);
}

#pragma mark Swizzled Method

-(BOOL)crashGuard_hasSuffix:(NSString *)str {
    if(!str){
        // 打印崩潰信息，棧信息 等
        NSLog(@"selector \"hasSuffix\" crash for the the suffix is nil!");
        return NO;
    } else {
        return [self crashGuard_hasSuffix:str];
    }
}

- (BOOL)crashGuard_hasPrefix:(NSString *)str {
    if(!str){
        // 打印崩潰信息，棧信息 等
        NSLog(@"selector \"hasPrefix\" crash for the the prefix is nil!");
        return NO;
    } else {
        return [self crashGuard_hasPrefix:str];
    }
}

（2）對NSArray的objectAtIndex:的crash預(yù)防如下：

#import "NSArray+CrashGuard.h"
#import <objc/runtime.h>

@implementation NSArray (CrashGuard)
+(void)load {
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        Method fromMethod = class_getInstanceMethod(objc_getClass("__NSArrayI"), @selector(objectAtIndex:));
        Method toMethod = class_getInstanceMethod(objc_getClass("__NSArrayI"), @selector(crashGuard_objectAtIndex:));
        method_exchangeImplementations(fromMethod, toMethod);
    });
}

#pragma mark Swizzled Method

-(id)crashGuard_objectAtIndex:(NSUInteger)index {
    if(self.count-1 < index) {
        // 打印崩潰信息，棧信息 等
        NSLog(@"selector \"objectAtIndex\" crash for the index beyond  the boundary!");
        return nil;
    } else {
        return [self crashGuard_objectAtIndex:index];
    }
}

@end

3）對NSMutableDictionary的setObject:forKey:的crash預(yù)防如下：

#import "NSMutableDictionary+CrashGuard.h"
#import <objc/runtime.h>

@implementation NSMutableDictionary (CrashGuard)
+(void)load {
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        Method fromMethod = class_getInstanceMethod(objc_getClass("__NSDictionaryM"), @selector(setObject:forKey:));
        Method toMethod = class_getInstanceMethod(objc_getClass("__NSDictionaryM"), @selector(crashGuard_setObject:forKey:));
        method_exchangeImplementations(fromMethod, toMethod);
    });
}

#pragma mark Swizzled Method

-(void)crashGuard_setObject:(id)object forKey:(NSString *)key {
    if(!object) {
        // 打印崩潰信息，棧信息 等
        NSLog(@"selector \"setObject:forKey:\" crash for the the object is nil!");
        
    } else {
        [self crashGuard_setObject:object forKey:key];
    }
    
}
@end

總結(jié)：

Container crash 類型和NSString類型的crash防護(hù)方案比較簡單，針對于NSArray／NSMutableArray／NSDictionary／NSMutableDictionary的一些常用的會導(dǎo)致崩潰的API進(jìn)行method swizzling，然后在swizzle的新方法中加入一些條件限制和判斷，從而讓這些API變的安全。當(dāng)然，在程序進(jìn)入這些swizzle的方法后，我們需要及時記錄并上傳相關(guān)的日志信息到后臺服務(wù)器，并及時review相關(guān)的內(nèi)容，將迭代中將有隱患的代碼改掉。