MWPhotoBrowser性能优化

最近在学习IOS开发下载了MWPhotoBrowser源码来研究, 运行的时候发现加载IPhone5 (ios7)系统相册数据的时候页面很卡,于是决定将它进行一下优化,在看了源码之后发现问题出在了MWPhoto.m这个文件中.

1.发现问题

加载系统相册数据的时候是使用的URL的形式来初始化数据的,这没什么问题,问题就出在了,没有区分是缩略图还是全屏图片啊.(MWPhotoBrowser图片的显示是区分缩略图显示还是全屏图片显示的,但是使用的图片都是全屏图片).源码里面默认都是加载的全屏图片,假如我要显示缩略图屏图片的时候给你来自一张全屏图片,而我实际只需要一张小小的缩略图,这不是白白浪费资源吗, 所以决定动手改造一下,我们首先来看看他的初始化方法,就是下面两个方法.貌似看不出什么问题.接着往下看..

// 这里没有区分是否为缩略图
+ (MWPhoto *)photoWithURL:(NSURL *)url {
    return [[MWPhoto alloc] initWithURL:url];
}
// 这里也没有区分是否为缩略图
- (id)initWithURL:(NSURL *)url {
    if ((self = [super init])) {
        self.photoURL = url;
    }
    return self;
}

看看它是怎么样加载图片的,首先来看看它是怎么加载系统相册里面的图片的,我们找到performLoadUnderlyingImageAndNotify这个方法,里面的代码
if ([[[_photoURL scheme] lowercaseString] isEqualToString:@”assets-library”]) 这一句就是判断是否为系统相册里面的图片. 如果是系统相册图片执行if里面的方法,这里貌似也没什么问题,我们接着往下看.来看看if之后调用的方法._performLoadUnderlyingImageAndNotifyWithAssetsLibraryURL

// Set the underlyingImage
- (void)performLoadUnderlyingImageAndNotify {

    // Get underlying image
    if (_image) {

        // We have UIImage!
        self.underlyingImage = _image;
        [self imageLoadingComplete];

    } else if (_photoURL) {

        // Check what type of url it is
        if ([[[_photoURL scheme] lowercaseString] isEqualToString:@"assets-library"]) {

            // Load from assets library
            [self _performLoadUnderlyingImageAndNotifyWithAssetsLibraryURL: _photoURL];

        } else if ([_photoURL isFileReferenceURL]) {

            // Load from local file async
            [self _performLoadUnderlyingImageAndNotifyWithLocalFileURL: _photoURL];

        } else {

            // Load async from web (using SDWebImage)
            [self _performLoadUnderlyingImageAndNotifyWithWebURL: _photoURL];

        }

    } else if (_asset) {

        // Load from photos asset
        [self _performLoadUnderlyingImageAndNotifyWithAsset: _asset targetSize:_assetTargetSize];

    } else {

        // Image is empty
        [self imageLoadingComplete];

    }
}

接下来就看到 if 语句里面调用的加载图片的方法.

// Load from asset library async
- (void)_performLoadUnderlyingImageAndNotifyWithAssetsLibraryURL:(NSURL *)url {
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        @autoreleasepool {
            @try {
                ALAssetsLibrary *assetslibrary = [[ALAssetsLibrary alloc] init];
                [assetslibrary assetForURL:url
                               resultBlock:^(ALAsset *asset){
                                   CGImageRef iref =  [[asset defaultRepresentation] fullScreenImage];
                                   if (iref) {
                                       self.underlyingImage = [UIImage imageWithCGImage:iref];
                                   }
                                   [self performSelectorOnMainThread:@selector(imageLoadingComplete) withObject:nil waitUntilDone:NO];
                               }
                              failureBlock:^(NSError *error) {
                                  self.underlyingImage = nil;
                                  MWLog(@"Photo from asset library error: %@",error);
                                  [self performSelectorOnMainThread:@selector(imageLoadingComplete) withObject:nil waitUntilDone:NO];
                              }];
            } @catch (NSException *e) {
                MWLog(@"Photo from asset library error: %@", e);
                [self performSelectorOnMainThread:@selector(imageLoadingComplete) withObject:nil waitUntilDone:NO];
            }
        }
    });
}

看到了吗,里面有下面这一句,这一句是将全屏图片加载出来,然后封装成UIImage. 问题就出在这里.

CGImageRef iref =  [[asset defaultRepresentation] fullScreenImage]; 

这一句没有区分是否为缩略图,假如我进入的是图片列表,需要加载缩略图,但是真是情况是加载全屏图片,这样会造成很大的资源浪费,而且会拖慢运行速度,所以解决办法是加一个属性,来区分是否为缩略图,来分别加载不同大小的图片

解决问题

首先在 MWPhoto.h 文件中添加属性

 @property (nonatomic) BOOL isThumb; //是否为缩略图

然后再把刚才那一句改一下改成下面这样

CGImageRef iref = self.isThumb?  [asset thumbnail]:[[asset defaultRepresentation] fullScreenImage];

这样就大功告成了. 再也不用担心加载系统相册卡顿的问题了…

最后既然我已经使用URL来加载系统图片了,为何不直接使用 ALAsset 来直接处理呢

所以有了下面的改造
MWPhoto.h 添加初始化方法,方法参数里面指定是否为缩略图

@property (nonatomic, strong) ALAsset *alAsset;
+ (MWPhoto *)photoWithALAsset:(ALAsset *)url isThumb:(BOOL) isThumb;
- (id)initWithALAsset:(ALAsset *)asset isThumb:(BOOL) isThumb;

MWPhoto.m 添加方法的实现

+(MWPhoto *)photoWithALAsset:(ALAsset *)asset isThumb:(BOOL)isThumb{
    return [[MWPhoto alloc]initWithALAsset:asset isThumb:isThumb];
}

-(id)initWithALAsset:(ALAsset *)asset isThumb:(BOOL)isThumb{
    if ((self = [super init])) {
        self.alAsset = asset;
        self.isThumb = isThumb;
    }
    return self;
}

然后改造一下MWPhoto.m中的performLoadUnderlyingImageAndNotify方法
添加 if(_alAsset){// 添加是否为系统图片的判断,然后判断中调用
_performLoadUnderlyingImageAndNotifyWithAssetsLibraryAlAsset 方法

// Set the underlyingImage
- (void)performLoadUnderlyingImageAndNotify {

    // Get underlying image
    if (_image) {

        // We have UIImage!
        self.underlyingImage = _image;
        [self imageLoadingComplete];

    } else if (_photoURL) {

        // Check what type of url it is
        if ([[[_photoURL scheme] lowercaseString] isEqualToString:@"assets-library"]) {

            // Load from assets library
            [self _performLoadUnderlyingImageAndNotifyWithAssetsLibraryURL: _photoURL];

        } else if ([_photoURL isFileReferenceURL]) {

            // Load from local file async
            [self _performLoadUnderlyingImageAndNotifyWithLocalFileURL: _photoURL];

        } else {

            // Load async from web (using SDWebImage)
            [self _performLoadUnderlyingImageAndNotifyWithWebURL: _photoURL];

        }

    } else if(_alAsset){// 添加是否为系统图片的判断
        // Load from photos asset
        [self _performLoadUnderlyingImageAndNotifyWithAssetsLibraryAlAsset: _alAsset];

    }else if (_asset) {

        // Load from photos asset
        [self _performLoadUnderlyingImageAndNotifyWithAsset: _asset targetSize:_assetTargetSize];

    } else {

        // Image is empty
        [self imageLoadingComplete];

    }
}

方法实现

// Load from asset library async
- (void)_performLoadUnderlyingImageAndNotifyWithAssetsLibraryAlAsset:(ALAsset *) asset {
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        @autoreleasepool {
            @try {
                CGImageRef iref = self.isThumb?  [asset thumbnail]:[[asset defaultRepresentation] fullScreenImage];
                if (iref) {
                    self.underlyingImage = [UIImage imageWithCGImage:iref];
                }
                [self performSelectorOnMainThread:@selector(imageLoadingComplete) withObject:nil waitUntilDone:NO];

            } @catch (NSException *e) {
                MWLog(@"Photo from asset library error: %@", e);
                [self performSelectorOnMainThread:@selector(imageLoadingComplete) withObject:nil waitUntilDone:NO];
            }
        }
    });
}

这次又进一步的优化了MWPhotoBrowser的加载性能, 还有MWPhotoBrowser选择图片时候, 会误选择图片问题的解决方案会在下一篇博客中继续讲解…

注: 无选择问题:
假设我点中一张图片然后向上或者向下滑动,这时候有可能会将这张图片勾选上, 假设我在快速滑动的时候,很容易误选择了不该选择的图片(比如)你懂得…