iOS WebView Memory Carsh

初步定为这个问题是 WebView Memory Carsh 的崩溃，这个也是我们项目中崩溃率的最主要点，其中因内存过大造成的 崩溃 也是一直烦着我们。

// Destroy UIWebView
- (void)destroyWebView {
    [self.webView loadHTMLString:@"" baseURL:nil];
    [self.webView stopLoading];
    [self.webView setDelegate:nil];
    [self.webView removeFromSuperview];
    [self setWebView:nil];
    
    [[NSURLCache sharedURLCache] removeAllCachedResponses];
    [[NSURLCache sharedURLCache] setDiskCapacity:0];
    [[NSURLCache sharedURLCache] setMemoryCapacity:0];
}

// UIWebViewDelegate Methods
- (void) webViewDidFinishLoad:(UIWebView *)webView {
    [[NSUserDefaults standardUserDefaults] setInteger:0 forKey:@"WebKitCacheModelPreferenceKey"];
    [[NSUserDefaults standardUserDefaults] setBool:NO forKey:@"WebKitDiskImageCacheEnabled"];
    [[NSUserDefaults standardUserDefaults] setBool:NO forKey:@"WebKitOfflineWebApplicationCacheEnabled"];
}

当收到内存警告时，同时释放一些

-(void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    [[NSURLCache sharedURLCache] removeAllCachedResponses];
}

然而上述并没有什么用。。。。
进一步分析

以下是我们内存警告的错误日志：

Crashed: com.apple.main-thread
0  libobjc.A.dylib                0x184abeb00 objc_object::release() + 16
1  CoreFoundation                 0x1857c0950 -[__NSSingleObjectArrayI dealloc] + 44
2  libobjc.A.dylib                0x184abf38c (anonymous namespace)::AutoreleasePoolPage::pop(void*) + 676
3  UIKitCore                      0x1b2eefdb0 -[UIView dealloc] + 964
4  UIKitCore                      0x1b2c44754 -[UITableViewCellContentView dealloc] + 76
5  UIKitCore                      0x1b2c4444c -[UITableViewCell .cxx_destruct] + 856
6  libobjc.A.dylib                0x184aa4478 object_cxxDestructFromClass(objc_object*, objc_class*) + 148
7  libobjc.A.dylib                0x184ab471c objc_destructInstance + 68
8  libobjc.A.dylib                0x184ab4784 object_dispose + 16
9  UIKitCore                      0x1b2aa0fac -[UIResponder dealloc] + 152
10 UIKitCore                      0x1b2eefdcc -[UIView dealloc] + 992
11 UIKitCore                      0x1b2c33374 -[UITableViewCell dealloc] + 332
12 CoreFoundation                 0x185833fc4 cow_cleanup + 112
13 CoreFoundation                 0x1857bc2f8 -[__NSArrayM dealloc] + 68
14 CoreFoundation                 0x1857ccb78 -[__NSDictionaryM removeAllObjects] + 620
15 UIKitCore                      0x1b2c6e8cc -[UITableView _purgeReuseQueues] + 128
16 CoreFoundation                 0x18584483c __CFNOTIFICATIONCENTER_IS_CALLING_OUT_TO_AN_OBSERVER__ + 20
17 CoreFoundation                 0x185844808 ___CFXRegistrationPost_block_invoke + 64
18 CoreFoundation                 0x185843cf8 _CFXRegistrationPost + 392
19 CoreFoundation                 0x1858439a4 ___CFXNotificationPost_block_invoke + 96
20 CoreFoundation                 0x1857bbb80 -[_CFXNotificationRegistrar find:object:observer:enumerator:] + 1404
21 CoreFoundation                 0x185843430 _CFXNotificationPost + 696
22 Foundation                     0x186254ca0 -[NSNotificationCenter postNotificationName:object:userInfo:] + 68
23 UIKitCore                      0x1b2a87848 -[UIApplication _performMemoryWarning] + 152
24 UIKitCore                      0x1b2a87a34 -[UIApplication _receivedMemoryNotification] + 140
25 libdispatch.dylib              0x18530e484 _dispatch_client_callout + 16
26 libdispatch.dylib              0x1852b182c _dispatch_continuation_pop$VARIANT$mp + 412
27 libdispatch.dylib              0x1852c1b9c _dispatch_source_invoke$VARIANT$mp + 1704
28 libdispatch.dylib              0x1852ba888 _dispatch_main_queue_callback_4CF$VARIANT$mp + 784
29 CoreFoundation                 0x185865ce4 __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 12
30 CoreFoundation                 0x185860bac __CFRunLoopRun + 1964
31 CoreFoundation                 0x1858600e0 CFRunLoopRunSpecific + 436
32 GraphicsServices               0x187ad9584 GSEventRunModal + 100
33 UIKitCore                      0x1b2a74c00 UIApplicationMain + 212
34 GearBest                       0x100e85c34 main (main.m:65)
35 libdyld.dylib                  0x18531ebb4 start + 4

注意看 App 收到Memory Warning 后会调用 [UIApplication _performMemoryWarning] 然后发通知给相应的页面告知我们需要处理了。

类似这种：

- (void)simulateMemoryWarning {
    UIApplication *app = [UIApplication sharedApplication];
    if ([app respondsToSelector:@selector(_performMemoryWarning)])
        [app performSelector:@selector(_performMemoryWarning)];
}

当我们的程序在第一次收到内存不足警告时，而又没有处理的情况下，内存不足情形依然存在，那么再次向我们程序发出内存不足的警告时，我们的程序将会被杀掉，也就崩溃了。

此时却发现了 是由于 当前 View 没有释放的问题，当前 Controller 释放了 View 却没有被释放，进一步查找还是 View 循环引用的问题，通过一番查找还是将 循环引用的问题解决后，发现这个崩溃率 大大降低（这种 bug 平时无法重现）。

当然，本来记录这篇文章的原因是想记录下 WebView Memory Carsh 的解决历程，类似直接加载：

- (void)loadHTMLString:(NSString *)string baseURL:(nullable NSURL *)baseURL;

当内容过大时，在 iPhone 6 之前的手机还是容易由于内存不足崩溃的。

所以此时问题并没有解决自己的问题，陆续寻找中 。。。