iOS 内存泄漏如何解决

下面是两个很少见的 UIViewController的属性:isBeingDismissed 当一个模态推送出来的 view controller 正在消失的时候, 为: true.isMovingFromParentViewController ,当一个 view controller 正在从它的父 view contrlller 中移除的时候(包括从系统的容器试图比如说 UINavigationController), 为true.如果这两个属性有一个是 true 的话, 这个 view controller 就会自动的被释放掉。我们不知道一个 view contrller 完成内部状态的改变，并且被 ARC 释放掉需要耗费多长的时间。为了简单起见，我们假设它不会超过两秒。

.现在看看下面的代码(文末会有OC版):extension UIViewController {    public func dch_checkDeallocation(afterDelay delay: TimeInterval = 2.0) {        let rootParentViewController = dch_rootParentViewController        // We don’t check `isBeingDismissed` simply on this view controller because it’s common        // to wrap a view controller in another view controller (e.g. in UINavigationController)        // and present the wrapping view controller instead.        if isMovingFromParentViewController || rootParentViewController.isBeingDismissed {            let type = type(of: self)            let disappearanceSource: String = isMovingFromParentViewController ? 'removed from its                     parent' : 'dismissed'            DispatchQueue.main.asyncAfter(deadline: .now() + delay, execute: { [weak self] in                assert(self == nil, '(type) not deallocated after being (disappearanceSource)')            })        }    }    private var dch_rootParentViewController: UIViewController {        var root = self        while let parent = root.parent {            root = parent        }        return root    }}在延时操作这个闭包中，我们首先通过 [weak self] 来避免这个闭包强引用self。然后通过断言让程序在 self 不为空的时候抛出异常。只有存在循环引用的情况下这个 view controller 才不为空。现在我们需要做的就是在 viewDidDisappear 中调用这个方法。只要是你需要检查它在消失后是不是被释放掉的 view controller 都需要添加这个方法。override func viewDidDisappear(_ animated: Bool) {    super.viewDidDisappear(animated)    dch_checkDeallocation()}如果发声了内存泄漏，我们就会得到下面的断言:这个时候，我们只需要打开 Xcode 的 Memory Graph Debugger 找到并且解决这些循环引用。

3.使用国人写的 MLeaksFinder 在每次发生内存泄漏的时候都会弹窗。并且没有代码侵入性，只需要使用 CocosPod 导入就可以了。

4.在使用图片资源的时候，少使用  imageNamed: 方法去获取使用频次不高的图片资源。因为使用 imageNamed:加载的图片资源会一直存在内存里面， 对内存的浪费也是巨大的。

5.上面的方法写了一个 OC 版本的：.h:#import @interface UIViewController (FindLeaks)// 默认为 NO@property (nonatomic) BOOL noCheckLeaks;@end.m:////  UIViewController+FindLeaks.m//  Leaks////  Created by sunny on 2017/8/27.//  Copyright ? 2017年 CepheusSun. All rights reserved.//#import 'UIViewController+FindLeaks.h'#import static const char *noCheckLeaksKey = 'noChechLeaksKey';@interface NSObject (MethodSwizzling)+ (void)sy_swizzleInstanceSelector:(SEL)origSelector                   swizzleSelector:(SEL)swizzleSelector;@end@implementation UIViewController (FindLeaks)#pragma mark - Binding Property- (BOOL)noCheckLeaks {    return [objc_getAssociatedObject(self, noCheckLeaksKey) boolValue];}- (void)setNoCheckLeaks:(BOOL)noCheckLeaks {    objc_setAssociatedObject(self, noCheckLeaksKey, [NSNumber numberWithBool:noCheckLeaks], OBJC_ASSOCIATION_RETAIN_NONATOMIC);}#pragma mark - Check+ (void)load {    #if DEBUG    [self sy_swizzleInstanceSelector:@selector(viewDidDisappear:) swizzleSelector:@selector(fl_viewDidDisappear:)];#endif}- (void)fl_viewDidDisappear:(BOOL)animated {    [self fl_viewDidDisappear:animated];    if (!self.noCheckLeaks) {        [self fl_checkDeallocationAfterDelay:2];    }}- (void)fl_checkDeallocationAfterDelay:(NSTimeInterval)delay {    UIViewController *root = [self fl_rootParentViewController];    if (self.isMovingFromParentViewController || root.isBeingDismissed) {        NSString *type = NSStringFromClass([self class]);        NSString *disappearanceSource = self.isMovingFromParentViewController ? @'removed from its parent' : @'dismissed';        __weak typeof(self) weakSelf = self;        dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delay * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{            NSString *assert = [NSString stringWithFormat:@'%@ not deallocated after being %@',             type, disappearanceSource];            NSAssert(weakSelf == nil,assert);        });    }}- (UIViewController *)fl_rootParentViewController {    UIViewController *root = self;    while (root.parentViewController) {        root = root.parentViewController;    }    return root;}@end@implementation NSObject (MethodSwizzling)+ (void)sy_swizzleInstanceSelector:(SEL)origSelector                   swizzleSelector:(SEL)swizzleSelector {    Method origMethod = class_getInstanceMethod(self, origSelector);    Method swizzleMethod = class_getInstanceMethod(self, swizzleSelector);  BOOL isAdd = class_addMethod(self, origSelector, method_getImplementation(swizzleMethod), method_getTypeEncoding(swizzleMethod));    if (!isAdd) {        method_exchangeImplementations(origMethod, swizzleMethod);    }else {        class_replaceMethod(self, swizzleSelector, method_getImplementation(origMethod), method_getTypeEncoding(origMethod));    }}@end只需要在不需要检查的方法中设置属性为 YES 就好了。