iOS 常见内存泄露修复

iOS 开发过程中内存泄露比较常见，如何发现这些内存泄露呢？我的建议是使用 AMLeaksFinder + Xcode instruments - leaks + Xcode Product - Analyze 去发现。这里不详述发现过程。
常见的内存泄露和修复方法如下所述。

block 内循环引用

情形 1：明显的循环引用

self.block = ^{
    self.str = @"leak";
};

修改方法：

__weak typeof(self)weakSelf = self; 
self.block = ^{
    weakSelf.str = @"leak";
};

情形 2：遗漏weakSelf的循环引用

__weak typeof(self)weakSelf = self; 
self.block = ^{
    weakSelf.str1 = @"1";
    self.str1 = @"3";
};

修改方法：

__weak typeof(self)weakSelf = self; 
self.block = ^{
    weakSelf.str1 = @"1";
    weakSelf.str1 = @"3";
};

情形 3：block内调用实例变量的循环引用

__weak typeof(self)weakSelf = self; 
self.block = ^{
    _str = @"1";
};

修改方法：

__weak typeof(self)weakSelf = self; 
self.block = ^{
    weakSelf->_str = @"1";
};

情形 4：block内嵌套block的循环引用

__weak typeof(self)weakSelf = self;
self.block = ^{
    __strong typeof(weakSelf)strongSelf = weakSelf;
    strongSelf.testObj = [TestObject new];
    strongSelf.testObj.completeBlock = ^{
        strongSelf.str = @"block";
    };
};
self.block();

修改方法：

__weak typeof(self)weakSelf = self;
self.block = ^{
    __strong typeof(weakSelf)strongSelf = weakSelf;
    strongSelf.testObj = [TestObject new];
    strongSelf.testObj.completeBlock = ^{
        weakSelf.str = @"block";
    };
};
self.block();

不用 weak 修饰 delegate 导致的内存泄露

@property (nonatomic, strong) id<TestLeakDelegate> delegate;

修改方法：

@property (nonatomic, weak) id<TestLeakDelegate> delegate;

使用 NSTimer 导致的内存泄露

self.timer = [NSTimer timerWithTimeInterval:1.0 target:self selector:@selector(triggerSelector) userInfo:nil repeats:YES];

修改方法：使用 NSProxy 作为中间者，弱引用 self。参考 YYWeakProxy

self.timer = [NSTimer timerWithTimeInterval:1.0 target:[YYWeakProxy proxyWithTarget:self] selector:@selector(triggerSelector) userInfo:nil repeats:YES];

OC 运行时方法导致的内存泄露，要使用 free 释放内存

Method *methods = class_copyMethodList([self class], &count);
free(methods);

unsigned int classCount = 0;
Class *classes = objc_copyClassList(&classCount);
free(classes);

char *argumentTypeEncoding = method_copyArgumentType(method, argumentIndex);
free(argumentTypeEncoding);

Ivar *ivars = class_copyIvarList(tryClass, &ivarCount);
free(ivars);

Protocol *__unsafe_unretained *protocols = objc_copyProtocolList(&prcount);
free(protocols);

unsigned int pcount;
objc_property_t *objcproperties = class_copyPropertyList(cls, &pcount);
free(objcproperties);

函数名包含create、alloc、copy字眼的以下类型都需要手动释放内存：

• CG类型的对象，需要手动执行释放操作CGxxxRelease(name)。
  例如：

CGColorSpaceRef cs = CGColorSpaceCreateDeviceGray(); CGColorSpaceRelease(cs);

CGImageRef image = [self.imageGenerator copyCGImageAtTime:time actualTime:NULL error:&error]; 
CGImageRelease(image);

CGImageRef imageRef = CGBitmapContextCreateImage(context);
CGImageRelease(imageRef);

CGContextRef ctx = CGBitmapContextCreate(data,width,height,8,rowBytes,colorSpace,kCGImageAlphaNoneSkipLast);
CGContextRelease(ctx);

• CF、CT类型对象，需要手动执行释放操作CFRelease(name)。例如：

CFNumberRef num = CFNumberCreate(kCFAllocatorDefault,kCFNumberSInt8Type,&number);
CFRelease(num);

CTTypesetterRef typesetter = CTTypesetterCreateWithAttributedString((__bridge CFAttributedStringRef)_attributedText);
CFRelease(typesetter);

CTTextAlignment alignment = kCTLeftTextAlignment;
CTParagraphStyleRef style = CTParagraphStyleCreate((CTParagraphStyleSetting[1]){
    {kCTParagraphStyleSpecifierAlignment, sizeof(alignment), &alignment}}
},1);
CFRelease(style);

• C语言代码中的malloc/calloc,需要需要手动执行释放操作free(name)。例如：

uint8_t* inputBuf = (uint8_t*)malloc(inputSize);
free(inputBuf);

void *buffer = calloc(bufferSize, 1);
free(buffer);

• CF、CT类型对象，需要手动执行释放操作CFRelease(name)。例如：

CFNumberRef num = CFNumberCreate(kCFAllocatorDefault,kCFNumberSInt8Type,&number);
CFRelease(num);

CTTypesetterRef typesetter = CTTypesetterCreateWithAttributedString((__bridge CFAttributedStringRef)_attributedText);
CFRelease(typesetter);

CTTextAlignment alignment = kCTLeftTextAlignment;
CTParagraphStyleRef style = CTParagraphStyleCreate((CTParagraphStyleSetting[1]){
    {kCTParagraphStyleSpecifierAlignment, sizeof(alignment), &alignment}}
},1);
CFRelease(style);

• C语言代码中的malloc/calloc,需要需要手动执行释放操作free(name)。例如：

uint8_t* inputBuf = (uint8_t*)malloc(inputSize);
free(inputBuf);

void *buffer = calloc(bufferSize, 1);
free(buffer);

子视图强引用父视图导致的内存泄露

TestView *testV = [[TestView alloc] initWithFrame:CGRectMake(100, 200, 100, 100)];
testV.block = ^{
    self;
};
[self.view addSubview:testV];

修改方法:

TestView *testV = [[TestView alloc] initWithFrame:CGRectMake(100, 200, 100, 100)];
__weak typeof(self)weakSelf = self;
testV.block = ^{
    weakSelf;
};
[self.view addSubview:testV];

OC 对象不明显的持有的 block 强引用导致的内存泄露

@interface TestObject : NSObject
- (void)callTest:(NSString *)test block:(dispatch_block_t)block;
@end

@interface TestObject ()
@property (nonatomic, copy) dispatch_block_t block;
@end

@implementation TestObject
- (void)callTest:(NSString *)test block:(dispatch_block_t)block {
    self.block = block;
}
@end

[self.testObj callTestTest:@"test" block:^{
    self;
}];

修改方法:

__weak typeof(self)weakSelf = self;
[self.testObj callTestTest:@"test" block:^{
    weakSelf;
}];

其他情形，如有补充，还请提出建议。