译 ios 使用运行时规避数组等越界导致程序崩溃
2019-01-15 本文已影响7人
瞌睡树懒
项目中经常遇到数组越界的情况，这是个很烦人的问题，并且面试中常遇到，就思考写了下如何避免这样的问题。
首先我们获取数组元素的方式分为:
NSArray *array = @[@1,@2];
NSLog(@"arrary: %@",[array objectAtIndex:2]);
NSLog(@"arrary: %@",array[2]);
NSMutableArray *mutArray = [NSMutableArray arrayWithArray:@[@1,@2]];
NSLog(@"NSMutableArray: %@",[mutArray objectAtIndex:2]);
NSLog(@"NSMutableArray: %@",mutArray[2]);
是的，通过objectAtIndex和[] 方式。
然后我们是不是第一个想法就是写分类然后重写？
嗯，我的确是试了一下，然后发现并没有用，系统这样提示我:
Category is implementing a method which will also be implemented by its primary class
WTF? 警告，说这里重写也没有用？那怎么办？
而且还有一个问题就是，objectAtIndex方法很明确了，那么[] 这是个什么鬼？这也能用方法来表示？是的。
有两种方式可以知道：
第一种直接看错误:
2017-12-29 19:25:36.510723+0800 OCTest[39152:4167702] *** Terminating app due to uncaught exception 'NSRangeException', reason: '*** -[__NSArrayI objectAtIndexedSubscript:]: index 3 beyond bounds [0 .. 1]'
*** First throw call stack:
(
0 CoreFoundation 0x00007fff4150700b __exceptionPreprocess + 171
1 libobjc.A.dylib 0x00007fff680e5c76 objc_exception_throw + 48
2 CoreFoundation 0x00007fff41548514 _CFThrowFormattedException + 202
3 CoreFoundation 0x00007fff415b9201 -[__NSArrayI objectAtIndexedSubscript:] + 97
4 OCTest 0x0000000100000e55 main + 245
5 libdyld.dylib 0x00007fff68cd5115 start + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException
我们人为越界了一下，发现了错误所在
[__NSArrayI objectAtIndexedSubscript:]
是的，这里告诉我们就是它发生了错误.
第二种：
在main.m文件中写下如下代码:
int main(int argc, const char * argv[]) {
@autoreleasepool {
NSArray *array = @[@1,@2];
NSLog(@"arrary: %@",[array objectAtIndex:2]);
NSLog(@"arrary: %@",array[3]);
}
return 0;
}
然后通过命令行:
clang -rewrite-objc main.m
得到
main.cpp
拉倒最后:
int main(int argc, const char * argv[]) {
/* @autoreleasepool */ { __AtAutoreleasePool __autoreleasepool;
NSArray *array = ((NSArray *(*)(Class, SEL, ObjectType _Nonnull const * _Nonnull, NSUInteger))(void *)objc_msgSend)(objc_getClass("NSArray"), sel_registerName("arrayWithObjects:count:"), (const id *)__NSContainer_literal(2U, ((NSNumber *(*)(Class, SEL, int))(void *)objc_msgSend)(objc_getClass("NSNumber"), sel_registerName("numberWithInt:"), 1), ((NSNumber *(*)(Class, SEL, int))(void *)objc_msgSend)(objc_getClass("NSNumber"), sel_registerName("numberWithInt:"), 2)).arr, 2U);
NSLog((NSString *)&__NSConstantStringImpl__var_folders_2d_q947d5pn4z3dfyq0j4vqsq840000gn_T_main_9976d7_mi_0,((id (*)(id, SEL, NSUInteger))(void *)objc_msgSend)((id)array, sel_registerName("objectAtIndexedSubscript:"), (NSUInteger)1));
NSLog((NSString *)&__NSConstantStringImpl__var_folders_2d_q947d5pn4z3dfyq0j4vqsq840000gn_T_main_9976d7_mi_1,((id (*)(id, SEL, NSUInteger))(void *)objc_msgSend)((id)array, sel_registerName("objectAtIndex:"), (NSUInteger)1));
}
return 0;
}
通过代码我们也知道了[]调用的方式:
sel_registerName("objectAtIndexedSubscript:")
里面的objectAtIndexedSubscript方法就是当我们使用[]的时候底层调用的方法。
当然，它也无法重写。
知道了原因，我们却无法重写，真是一个悲伤的故事。于是我找啊找啊，就找到了一种可以替代方法的方法。不给上，哥就不上了? 那也太怂了是吧。
我找到的就是runtime中的替换方法。
官方解释网址:
https://developer.apple.com/documentation/objectivec/1418530-class_getinstancemethod
Method class_getInstanceMethod(Class cls, SEL name);
Returns a specified instance method for a given class.
为给定的类返回指定的实例方法。
我们先通过这个方法获取指定的实例方法
https://developer.apple.com/documentation/objectivec/1418769-method_exchangeimplementations
void method_exchangeImplementations(Method m1, Method m2);
Exchanges the implementations of two methods.
交换两种方法的实现。
然后我们再自己实现个方法，这方法里面我们做一下规避操作。比如用try catch把异常给捕捉起来，然后打上日志。就不用担心会崩溃，也不知道哪里发生了错误。当然具体的方法要根据业务场景自我实现。
下面的__NSArrayI 和__NSArrrayM分别代表不可变数组和可变数组的真实类型
NSLog(@"type of array:%@",[array class]);
NSLog(@"type of mutableArray:%@",[mArray class]);
结果如下:
2017-12-29 19:46:08.048887+0800 OCTest[39319:4202006] type of array:__NSArrayI
2017-12-29 19:46:08.048905+0800 OCTest[39319:4202006] type of mutableArray:__NSArrayM
通过runtime的method swizzling 交换方法的实现 提前判断方法的参数是否符合要求
#import "NSArray+LXSRuntime.h"
#import <objc/runtime.h>
@implementation NSArray (LXSRuntime)
+(void)load
{
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
// 替换不可变数组中的方法 objectAtIndex
Method oldObjectAtIndex = class_getInstanceMethod(objc_getClass("__NSArrayI"), @selector(objectAtIndex:));
Method safeObjectAtIndex = class_getInstanceMethod(objc_getClass("__NSArrayI"), @selector(safeObjectAtIndex:));
method_exchangeImplementations(oldObjectAtIndex, safeObjectAtIndex);
// 替换不可变数组中的方法 []调用的方法
Method oldMutableObjectAtIndex = class_getInstanceMethod(objc_getClass("__NSArrayI"), @selector(objectAtIndexedSubscript:));
Method safeMutableObjectAtIndex = class_getInstanceMethod(objc_getClass("__NSArrayI"), @selector(safeObjectAtIndexedSubscript:));
method_exchangeImplementations(oldMutableObjectAtIndex, safeMutableObjectAtIndex);
// 替换可变数组中的方法 objectAtIndex
Method oldMObjectAtIndex = class_getInstanceMethod(objc_getClass("__NSArrayM"), @selector(objectAtIndex:));
Method safeMObjectAtIndex = class_getInstanceMethod(objc_getClass("__NSArrayM"), @selector(safeMutableObjectAtIndex:));
method_exchangeImplementations(oldMObjectAtIndex, safeMObjectAtIndex);
// 替换可变数组中的方法 []调用的方法
Method oldMMutableObjectAtIndex = class_getInstanceMethod(objc_getClass("__NSArrayM"), @selector(objectAtIndexedSubscript:));
Method safeMMutableObjectAtIndex = class_getInstanceMethod(objc_getClass("__NSArrayM"), @selector(safeMutableObjectAtIndexedSubscript:));
method_exchangeImplementations(oldMMutableObjectAtIndex, safeMMutableObjectAtIndex);
Method sourceMethod2 = class_getInstanceMethod(objc_getClass("__NSArrayM"), @selector(removeObjectAtIndex:));
Method destMethod2 = class_getInstanceMethod(objc_getClass("__NSArrayM"), @selector(safeRemoveObjectAtIndex:));
method_exchangeImplementations(sourceMethod2, destMethod2);
Method sourceMethod3 = class_getInstanceMethod(objc_getClass("__NSArrayM"), @selector(insertObject:atIndex:));
Method destMethod3 = class_getInstanceMethod(objc_getClass("__NSArrayM"), @selector(safeInsertObject:atIndex:));
method_exchangeImplementations(sourceMethod3, destMethod3);
Method sourceMethod4 = class_getInstanceMethod(objc_getClass("__NSArrayM"), @selector(replaceObjectAtIndex:withObject:));
Method destMethod4 = class_getInstanceMethod(objc_getClass("__NSArrayM"), @selector(safeReplaceObjectAtIndex:withObject:));
method_exchangeImplementations(sourceMethod4, destMethod4);
});
}
#pragma mark - 数组的安全处理
- (id)safeObjectAtIndex:(NSUInteger)index{
if (index > self.count - 1 || !self.count){
@try {
return [self safeObjectAtIndex:index];
} @catch (NSException *exception) {
NSLog(@"不可数组越界了");
return nil;
} @finally {
}
}
else{
return [self safeObjectAtIndex:index];
}
}
- (id)safeObjectAtIndexedSubscript:(NSUInteger)index{
if (index > self.count - 1 || !self.count){
@try {
return [self safeObjectAtIndexedSubscript:index];
} @catch (NSException *exception) {
NSLog(@"不可数组越界了");
return nil;
} @finally {
}
}
else{
return [self safeObjectAtIndexedSubscript:index];
}
}
- (id)safeMutableObjectAtIndex:(NSUInteger)index{
if (index > self.count - 1 || !self.count){
@try {
return [self safeMutableObjectAtIndex:index];
} @catch (NSException *exception) {
NSLog(@"可变数组越界了");
return nil;
} @finally {
}
}
else{
return [self safeMutableObjectAtIndex:index];
}
}
- (id)safeMutableObjectAtIndexedSubscript:(NSUInteger)index{
if (index > self.count - 1 || !self.count){
@try {
return [self safeMutableObjectAtIndexedSubscript:index];
} @catch (NSException *exception) {
NSLog(@"可变数组越界了");
return nil;
} @finally {
}
}
else{
return [self safeMutableObjectAtIndexedSubscript:index];
}
}
-(void)safeRemoveObjectAtIndex:(NSInteger)index
{
if (self.count <= index) {
NSLog(@"Runtime Warning:index %li out of bound",index);
return;
}
[self safeRemoveObjectAtIndex:index];
}
-(void)safeInsertObject:(id)object atIndex:(NSInteger)index
{
if (!object) {
NSLog(@"Runtime Warning:insert object can not be nil");
return;
}
if (self.count < index) {
NSLog(@"Runtime Warning:insert object at index %li out of bound",index);
return;
}
[self safeInsertObject:object atIndex:index];
}
-(void)safeReplaceObjectAtIndex:(NSInteger)index withObject:(id)object
{
if (index >= self.count) {
NSLog(@"Runtime Warning:index %li out of bound",index);
return;
}
if (!object) {
NSLog(@"Runtime Warning:object can not be empty");
return;
}
[self safeReplaceObjectAtIndex:index withObject:object];
}
@end
