一个小问题

我的浏览器在搭建好基本UI后运行还算正常。但添加了自动旋转代码后，开始报错。即使关闭Xcode，在模拟器上独立运行app，也只能坚持不到一分钟就闪退。

错误代码：

***Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: ': An -observeValueForKeyPath:ofObject:change:context: message was received but not handled.
Key path: estimatedProgress
Observed object: ; layer = >
  Change: {
  kind = 1;
  new = "0.6176357155547082";
  }
  Context: 0x0'
  ***First throw call stack:
  (
  0   CoreFoundation                      0x000000010b7a4c65 __exceptionPreprocess + 165
  1   libobjc.A.dylib                     0x000000010b43dbb7 objc_exception_throw + 45
  2   CoreFoundation                      0x000000010b7a4b9d +[NSException raise:format:] + 205
  3   Foundation                          0x000000010b06acaf -[NSObject(NSKeyValueObserving)observeValueForKeyPath:ofObject:change:context:] + 73
  4   NewBrowserProject                   0x000000010aefa246 -[ViewController observeValueForKeyPath:ofObject:change:context:] + 1030
  5   Foundation                          0x000000010af9ad96 NSKeyValueNotifyObserver + 356
  6   Foundation                          0x000000010af99fbd NSKeyValueDidChange + 466
  7   Foundation                          0x000000010af9e6df -[NSObject(NSKeyValueObserverNotification) didChangeValueForKey:] + 118
  8   WebKit                              0x000000010d2c47d1 _ZN6WebKit13PageLoadState13commitChangesEv + 1133
  9   WebKit                              0x000000010d227dc6 _ZN6WebKit12WebPageProxy17didChangeProgressEd + 74
  10  WebKit                              0x000000010d23a96c _ZN6WebKit12WebPageProxy17didReceiveMessageEPN3IPC10ConnectionERNS1_14MessageDecoderE + 2976
  11  WebKit                              0x000000010d12df58 _ZN3IPC18MessageReceiverMap15dispatchMessageEPNS_10ConnectionERNS_14MessageDecoderE + 120
  12  WebKit                              0x000000010d26cd9c _ZN6WebKit15WebProcessProxy17didReceiveMessageEPN3IPC10ConnectionERNS1_14MessageDecoderE + 24
  13  WebKit                              0x000000010d0b5baa _ZN3IPC10Connection15dispatchMessageENSt3__110unique_ptrINS_14MessageDecoderENS1_14default_deleteIS3_EEEE + 94
  14  WebKit                              0x000000010d0b85c4 _ZN3IPC10Connection18dispatchOneMessageEv + 110
  15  JavaScriptCore                      0x00000001153c1436 _ZN3WTF7RunLoop11performWorkEv + 454
  16  JavaScriptCore                      0x00000001153c1cea _ZN3WTF7RunLoop11performWorkEPv + 26
  17  CoreFoundation                      0x000000010b6d8431 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 17
  18  CoreFoundation                      0x000000010b6ce2fd __CFRunLoopDoSources0 + 269
  19  CoreFoundation                      0x000000010b6cd934 __CFRunLoopRun + 868
  20  CoreFoundation                      0x000000010b6cd366 CFRunLoopRunSpecific + 470
  21  GraphicsServices                    0x0000000110264a3e GSEventRunModal + 161
  22  UIKit                               0x000000010bddf8c0 UIApplicationMain + 1282
  23  NewBrowserProject                   0x000000010af00aaf main + 111
  24  libdyld.dylib                       0x000000010e5fb145 start + 1
  25  ???                                 0x0000000000000001 0x0 + 1
 )
libc++abi.dylib: terminating with uncaught exception of type NSException
(lldb)

看来是上一篇提到的添加进度条的代码出现了问题。
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {

  if ([keyPath isEqualToString:@"estimatedProgress"] && object == self.webView) {
       [self.loadingProgress setAlpha:1.0f];
       [self.loadingProgress setProgress:self.webView.estimatedProgress animated:YES];
       if(self.webView.estimatedProgress >= 1.0f) {
                  [UIView animateWithDuration:0.3 
                                        delay:0.3
                                     options:UIViewAnimationOptionCurveEaseOut
                                   animations:^ {
                         [self.loadingProgress setAlpha:0.0f];
                         }
                                   completion:^(BOOL finished) {
                         [self.loadingProgress setProgress:0.0f animated:NO];
                         }
                  ];
      }
 }else {
       [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
 }
}

这段代码在WKWebView的estimatedProgress属性发生变化时，显示UIProgressView控件，并当estimatedProgress属性为1时消失。

我的代码问题在于：设备每次旋转后，app都会移除WKWebView控件，并重新添加新的WKWebView控件。其estimatedProgress属性出现了从1到0的情况，对于这个观察事件来讲却无法作出反应，因为我将UIProgressView控件添加到了WKWebView控件上，随之移除并重新生成。

解决办法是，不再对WKWebView做 移除并重新生成 的老办法，而是直接设置setAutoresizingMask:属性。