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
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();
情形 5：block内调用 super 方法
self.block = ^{
[super xxx];
};
修改方法：
__weak typeof(self)weakSelf = self;
self.block = ^{
[weakSelf xxx];
};
- (void)xxx {
[super xxx];
}
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);
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
ViewController.m
[self.testObj callTestTest:@"test" block:^{
self;
}];
修改方法:
...
ViewController.m
__weak typeof(self)weakSelf = self;
[self.testObj callTest:@"test" block:^{
weakSelf;
}];
单例不明显的持有的 block 强引用导致的内存泄露
@interface SingletonManager ()
@property (nonatomic, copy) dispatch_block_t block;
@end
static SingletonManager *manager = nil;
@implementation SingletonManager
+ (instancetype)shareManager {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
manager = [[SingletonManager alloc] init];
});
return manager;
}
- (void)addBlock:(dispatch_block_t)block {
self.block = block;
}
@end
ViewController.m
[[SingletonManager shareManager] addBlock:^{
self;
}];
修改方法:
...
ViewController.m
__weak typeof(self)weakSelf = self;
[[SingletonManager shareManager] addBlock:^{
weakSelf;
}];
其他情形，如有补充，还请提出建议。
