iOS --- 使用runtime解决3D Touch导致UIImagePicker崩溃的问题

UIImagePickerController是iOS中自带的系统相册选择器, 使用起来非常简便.

UIImagePickerController

UIImagePickerController *imagePickerController = [[UIImagePickerController alloc] init];// 设置sourceType为系统相册, 如果使用Camera请对应修改该属性.imagePickerController.sourceType = UIImagePickerControllerSourceTypePhotoLibrary;imagePickerController.allowsEditing = YES;imagePickerController.delegate = self;[self presentViewController:imagePickerController animated:YES completion:nil];

UIImagePickerController本身继承自UINavigationController, 因此不能将其简单视作一个UIViewController来看待.
了UINavigationControllerDelegate和UIImagePickerControllerDelegate协议, 包含了由三个ViewController组成的导航视图, 我们通过打印其viewControllers即可看出来:

(lldb) po [picker viewControllers]<__NSArrayI 0x146b31140>(    <PUUIAlbumListViewController: 0x14609a200>,    <PUUIPhotosAlbumViewController: 0x1458e5a00>,    <PUUIImageViewController: 0x1468f1ad0>)

UIImagePickerControllerDelegate

UIImagePickerControllerDelegate协议有如下三个代理方法.

__TVOS_PROHIBITED @protocol UIImagePickerControllerDelegate<NSObject>@optional// The picker does not dismiss itself; the client dismisses it in these callbacks.// The delegate will receive one or the other, but not both, depending whether the user// confirms or cancels.- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingImage:(UIImage *)image editingInfo:(nullable NSDictionary<NSString *,id> *)editingInfo NS_DEPRECATED_IOS(2_0, 3_0);- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary<NSString *,id> *)info;- (void)imagePickerControllerDidCancel:(UIImagePickerController *)picker;

其中info包含了所选取照片的基本信息, 如下:

// info dictionary keysUIKIT_EXTERN NSString *const UIImagePickerControllerMediaType __TVOS_PROHIBITED;      // an NSString (UTI, i.e. kUTTypeImage)UIKIT_EXTERN NSString *const UIImagePickerControllerOriginalImage __TVOS_PROHIBITED;  // a UIImageUIKIT_EXTERN NSString *const UIImagePickerControllerEditedImage __TVOS_PROHIBITED;    // a UIImageUIKIT_EXTERN NSString *const UIImagePickerControllerCropRect __TVOS_PROHIBITED;       // an NSValue (CGRect)UIKIT_EXTERN NSString *const UIImagePickerControllerMediaURL __TVOS_PROHIBITED;       // an NSURLUIKIT_EXTERN NSString *const UIImagePickerControllerReferenceURL        NS_AVAILABLE_IOS(4_1) __TVOS_PROHIBITED;  // an NSURL that references an asset in the AssetsLibrary frameworkUIKIT_EXTERN NSString *const UIImagePickerControllerMediaMetadata       NS_AVAILABLE_IOS(4_1) __TVOS_PROHIBITED;  // an NSDictionary containing metadata from a captured photoUIKIT_EXTERN NSString *const UIImagePickerControllerLivePhoto NS_AVAILABLE_IOS(9_1) __TVOS_PROHIBITED;  // a PHLivePhoto}

当在系统相册中选取了照片之后, 会调用imagePickerController:didFinishPickingMediaWithInfo:方法, 在其中可以添加对该照片的一些操作, 如写入相册等.

- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary<NSString *,id> *)info {    UIImage *originalImage = info[UIImagePickerControllerOriginalImage];    UIImage *editedImage = info[UIImagePickerControllerEditedImage];    UIImage *savedImage = editedImage ?: originalImage;    if (picker.sourceType == UIImagePickerControllerSourceTypeCamera) {        UIImageWriteToSavedPhotosAlbum(savedImage, nil, nil, nil);    }    __weak ViewController *weakSelf = self;    [picker dismissViewControllerAnimated:YES completion:^{        weakSelf.imageView.image = savedImage;    }];}

并且UIImagePickerController自身并不会dismiss, 需要我们自己调用, 并且通过回调的方式将照片进行相应的处理.
上边的代码, 即在UIImagePickerController的dismiss操作之后, 将照片放置到UIImageView中.

自定义UIImagePickerController

创建一个UIViewController, 继承自UIImagePickerController, 并实现相关协议方法, 即可以自定义一个相册选择器.
不过实际上依然只是对UIImagePickerController进行了一次包装而已.
请参考demo:
https://github.com/icetime17/Playground/tree/master/DemoUIImagePicker

另外, 可以使用PhotoKit框架, 结合UICollectionView来实现真正意义上的自定义相册.
参考博客:
iOS — 使用PhotoKit代替ALAssetsLibrary来管理相册资源

问题

3D Touch

3D Touch是iPhone 6s/6splus设备才有的特点, 在系统相册中长按一个照片, 可触发3D Touch相关的操作.
而在没有3D Touch的设备中, 在系统相册中长按一个照片, 会导致crash. 这看起来像是iOS系统的一个bug.

原因在于:
触发3D Touch操作后, PUPhotosGridViewController的previewingContext:viewControllerForLocation:未实现, 所以导致crash.

解决方法:
使用runtime来实现method swizzling, 即在runtime中将该方法替换.
使用method_exchangeImplementations(originalMethod, replacementMethod);方法即可实现.

首先, 封装一个方法用于实现method swizzling

- (void)replaceSelectorForClass:(Class)cls                  SelectorOriginal:(SEL)original                   SelectorReplace:(SEL)replacement                    withBlock:(id)block {    IMP implementation = imp_implementationWithBlock(block);    Method originalMethod = class_getInstanceMethod(cls, original);    class_addMethod(cls, replacement, implementation, method_getTypeEncoding(originalMethod));    Method replacementMethod = class_getInstanceMethod(cls, replacement);    if (class_addMethod(cls, original, method_getImplementation(replacementMethod), method_getTypeEncoding(replacementMethod))) {        class_replaceMethod(cls, replacement, method_getImplementation(originalMethod), method_getTypeEncoding(originalMethod));    } else {        method_exchangeImplementations(originalMethod, replacementMethod);    }}

在AppDelegate的application:didFididFinishLaunchingWithOptions:方法中, 进行method swizzling:

- (void)preventImagePickerCrashOn3DTouch {    // Load PhotosUI and bail if 3D Touch is unavailable.    // (UIViewControllerPreviewing may be redundant,    // as PUPhotosGridViewController only seems to exist on iOS 9,    // but I'm being cautious.)    NSString *photosUIPath = @"/System/Library/Frameworks/PhotosUI.framework";    NSBundle *photosUI = [NSBundle bundleWithPath:photosUIPath];    Class photosClass = [photosUI classNamed:@"PUPhotosGridViewController"];    if (!(photosClass && objc_getProtocol("UIViewControllerPreviewing"))) {        return;    }#pragma clang diagnostic push#pragma clang diagnostic ignored "-Wundeclared-selector"    SEL selector = @selector(ab_previewingContext:viewControllerForLocation:);    [self replaceSelectorForClass:photosClass                 SelectorOriginal:@selector(previewingContext:viewControllerForLocation:)                  SelectorReplace:selector                        withBlock:^UIViewController *(id self, id<UIViewControllerPreviewing> previewingContext, CGPoint location) {        // Default implementation throws on iOS 9.0 and 9.1.        @try {            MTLog(@"Replace method at runtime to prevent UIImagePicker crash on 3D Touch.");            return ((UIViewController *(*)(id, SEL, id, CGPoint))objc_msgSend)(self, selector, previewingContext, location);        } @catch (NSException *e) {            return nil;        }    }];#pragma clang diagnostic pop}

这样, 即可成功解决3D Touch导致系统的UIImagePickerController崩溃的问题.