优化滑动帧数，我这里测试iOS89目前帧数平均在58，iOS7平均帧数在57,媲美QQ的图片选择器滑动帧数，比微信的帧数高10左右

TZImagePickerController.podspec

 Pod::Spec.new do |s|
   s.name         = "TZImagePickerController"
-  s.version      = "1.3.5"
+  s.version      = "1.4.0"
   s.summary      = "A clone of UIImagePickerController, support picking multiple photos、original photo and video"
   s.homepage     = "https://github.com/banchichen/TZImagePickerController"
   s.license      = "MIT"
   s.author       = { "banchichen" => "736420282@qq.com" }
   s.platform     = :ios
   s.ios.deployment_target = "6.0"
-  s.source       = { :git => "https://github.com/banchichen/TZImagePickerController.git", :tag => "1.3.5" }
+  s.source       = { :git => "https://github.com/banchichen/TZImagePickerController.git", :tag => "1.4.0" }
   s.requires_arc = true
   s.resources    = "TZImagePickerController/TZImagePickerController/*.{png,xib,nib,bundle}"
   s.source_files = "TZImagePickerController/TZImagePickerController/*.{h,m}"

TZImagePickerController/TZImagePickerController/TZAssetCell.h

@@ -7,6 +7,7 @@
 //
 
 #import <UIKit/UIKit.h>
+#import <Photos/Photos.h>
 
 typedef enum : NSUInteger {
     TZAssetCellTypePhoto = 0,
@@ -22,7 +23,8 @@ typedef enum : NSUInteger {
 @property (nonatomic, strong) TZAssetModel *model;
 @property (nonatomic, copy) void (^didSelectPhotoBlock)(BOOL);
 @property (nonatomic, assign) TZAssetCellType type;
-
+@property (nonatomic, copy) NSString *representedAssetIdentifier;
+@property (nonatomic, assign) PHImageRequestID imageRequestID;
 @end
 
 

TZImagePickerController/TZImagePickerController/TZAssetCell.m

@@ -35,9 +35,29 @@
 
 - (void)setModel:(TZAssetModel *)model {
     _model = model;
-    [[TZImageManager manager] getPhotoWithAsset:model.asset photoWidth:self.tz_width completion:^(UIImage *photo, NSDictionary *info, BOOL isDegraded) {
-        self.imageView.image = photo;
+    if (!iOS8Later) {
+        self.representedAssetIdentifier = [[TZImageManager manager] getAssetIdentifier:model.asset];
+    }
+    PHImageRequestID imageRequestID = [[TZImageManager manager] getPhotoWithAsset:model.asset photoWidth:self.tz_width completion:^(UIImage *photo, NSDictionary *info, BOOL isDegraded) {
+        // Set the cell's thumbnail image if it's still showing the same asset.
+        if (!iOS8Later) {
+            self.imageView.image = photo; return;
+        }
+        if ([self.representedAssetIdentifier isEqualToString:[[TZImageManager manager] getAssetIdentifier:model.asset]]) {
+            self.imageView.image = photo;
+        } else {
+            NSLog(@"this cell is showing other asset");
+            [[PHImageManager defaultManager] cancelImageRequest:self.imageRequestID];
+        }
+        if (!isDegraded) {
+            self.imageRequestID = 0;
+        }
     }];
+    if (imageRequestID && self.imageRequestID && imageRequestID != self.imageRequestID) {
+        [[PHImageManager defaultManager] cancelImageRequest:self.imageRequestID];
+        NSLog(@"cancelImageRequest %d",self.imageRequestID);
+    }
+    self.imageRequestID = imageRequestID;
     self.selectPhotoButton.selected = model.isSelected;
     self.selectImageView.image = self.selectPhotoButton.isSelected ? [UIImage imageNamedFromMyBundle:@"photo_sel_photoPickerVc.png"] : [UIImage imageNamedFromMyBundle:@"photo_def_photoPickerVc.png"];
     self.type = TZAssetCellTypePhoto;

TZImagePickerController/TZImagePickerController/TZImageManager.h

@@ -33,8 +33,8 @@
 
 /// Get photo 获得照片
 - (void)getPostImageWithAlbumModel:(TZAlbumModel *)model completion:(void (^)(UIImage *postImage))completion;
-- (void)getPhotoWithAsset:(id)asset completion:(void (^)(UIImage *photo,NSDictionary *info,BOOL isDegraded))completion;
-- (void)getPhotoWithAsset:(id)asset photoWidth:(CGFloat)photoWidth completion:(void (^)(UIImage *photo,NSDictionary *info,BOOL isDegraded))completion;
+- (PHImageRequestID)getPhotoWithAsset:(id)asset completion:(void (^)(UIImage *photo,NSDictionary *info,BOOL isDegraded))completion;
+- (PHImageRequestID)getPhotoWithAsset:(id)asset photoWidth:(CGFloat)photoWidth completion:(void (^)(UIImage *photo,NSDictionary *info,BOOL isDegraded))completion;
 - (void)getOriginalPhotoWithAsset:(id)asset completion:(void (^)(UIImage *photo,NSDictionary *info))completion;
 
 /// Save photo 保存照片
@@ -52,4 +52,6 @@
 /// Judge is a assets array contain the asset 判断一个assets数组是否包含这个asset
 - (BOOL)isAssetsArray:(NSArray *)assets containAsset:(id)asset;
 
+- (NSString *)getAssetIdentifier:(id)asset;
+
 @end

TZImagePickerController/TZImagePickerController/TZImageManager.m

@@ -17,12 +17,21 @@
 
 @implementation TZImageManager
 
+static CGSize AssetGridThumbnailSize;
+
 + (instancetype)manager {
     static TZImageManager *manager;
     static dispatch_once_t onceToken;
     dispatch_once(&onceToken, ^{
         manager = [[self alloc] init];
         manager.cachingImageManager = [[PHCachingImageManager alloc] init];
+        manager.cachingImageManager.allowsCachingHighQualityImages = NO;
+        
+        CGFloat scale = [UIScreen mainScreen].scale;
+        CGFloat screenWidth = [UIScreen mainScreen].bounds.size.width;
+        CGFloat margin = 4;
+        CGFloat itemWH = (screenWidth - 2 * margin - 4) / 4 - margin;
+        AssetGridThumbnailSize = CGSizeMake(itemWH * scale, itemWH * scale);
     });
     return manager;
 }
@@ -298,20 +307,25 @@
 #pragma mark - Get Photo
 
 /// Get photo 获得照片本身
-- (void)getPhotoWithAsset:(id)asset completion:(void (^)(UIImage *, NSDictionary *, BOOL isDegraded))completion {
-    [self getPhotoWithAsset:asset photoWidth:[UIScreen mainScreen].bounds.size.width completion:completion];
+- (PHImageRequestID)getPhotoWithAsset:(id)asset completion:(void (^)(UIImage *, NSDictionary *, BOOL isDegraded))completion {
+    return [self getPhotoWithAsset:asset photoWidth:[UIScreen mainScreen].bounds.size.width completion:completion];
 }
 
-- (void)getPhotoWithAsset:(id)asset photoWidth:(CGFloat)photoWidth completion:(void (^)(UIImage *, NSDictionary *, BOOL isDegraded))completion {
+- (PHImageRequestID)getPhotoWithAsset:(id)asset photoWidth:(CGFloat)photoWidth completion:(void (^)(UIImage *, NSDictionary *, BOOL isDegraded))completion {
     if (photoWidth > 600) photoWidth = 600.0;
     if ([asset isKindOfClass:[PHAsset class]]) {
-        PHAsset *phAsset = (PHAsset *)asset;
-        CGFloat aspectRatio = phAsset.pixelWidth / (CGFloat)phAsset.pixelHeight;
-        CGFloat multiple = [UIScreen mainScreen].scale;
-        CGFloat pixelWidth = photoWidth * multiple;
-        CGFloat pixelHeight = pixelWidth / aspectRatio;
-        
-        [[PHImageManager defaultManager] requestImageForAsset:asset targetSize:CGSizeMake(pixelWidth, pixelHeight) contentMode:PHImageContentModeAspectFit options:nil resultHandler:^(UIImage * _Nullable result, NSDictionary * _Nullable info) {
+        CGSize imageSize;
+        if (photoWidth < 150) {
+            imageSize = AssetGridThumbnailSize;
+        } else {
+            PHAsset *phAsset = (PHAsset *)asset;
+            CGFloat aspectRatio = phAsset.pixelWidth / (CGFloat)phAsset.pixelHeight;
+            CGFloat multiple = [UIScreen mainScreen].scale;
+            CGFloat pixelWidth = photoWidth * multiple;
+            CGFloat pixelHeight = pixelWidth / aspectRatio;
+            imageSize = CGSizeMake(pixelWidth, pixelHeight);
+        }
+       PHImageRequestID imageRequestID = [[PHImageManager defaultManager] requestImageForAsset:asset targetSize:imageSize contentMode:PHImageContentModeAspectFill options:nil resultHandler:^(UIImage * _Nullable result, NSDictionary * _Nullable info) {
             BOOL downloadFinined = (![[info objectForKey:PHImageCancelledKey] boolValue] && ![info objectForKey:PHImageErrorKey]);
             if (downloadFinined && result) {
                 result = [self fixOrientation:result];
@@ -323,7 +337,7 @@
                 option.networkAccessAllowed = YES;
                 [[PHImageManager defaultManager] requestImageDataForAsset:asset options:option resultHandler:^(NSData * _Nullable imageData, NSString * _Nullable dataUTI, UIImageOrientation orientation, NSDictionary * _Nullable info) {
                     UIImage *resultImage = [UIImage imageWithData:imageData scale:0.1];
-                    resultImage = [self scaleImage:resultImage toSize:CGSizeMake(pixelWidth, pixelHeight)];
+                    resultImage = [self scaleImage:resultImage toSize:imageSize];
                     if (resultImage) {
                         resultImage = [self fixOrientation:resultImage];
                         if (completion) completion(resultImage,info,[[info objectForKey:PHImageResultIsDegradedKey] boolValue]);
@@ -331,24 +345,30 @@
                 }];
             }
         }];
+        return imageRequestID;
     } else if ([asset isKindOfClass:[ALAsset class]]) {
         ALAsset *alAsset = (ALAsset *)asset;
-        ALAssetRepresentation *assetRep = [alAsset defaultRepresentation];
-        CGImageRef thumbnailImageRef = alAsset.aspectRatioThumbnail;
-        UIImage *thumbnailImage = [UIImage imageWithCGImage:thumbnailImageRef scale:1.0 orientation:UIImageOrientationUp];
-        if (completion) completion(thumbnailImage,nil,YES);
-        
-        if (photoWidth == [UIScreen mainScreen].bounds.size.width) {
-            dispatch_async(dispatch_get_global_queue(0,0), ^{
-                CGImageRef fullScrennImageRef = [assetRep fullScreenImage];
-                UIImage *fullScrennImage = [UIImage imageWithCGImage:fullScrennImageRef scale:1.0 orientation:UIImageOrientationUp];
+        dispatch_async(dispatch_get_global_queue(0,0), ^{
+            CGImageRef thumbnailImageRef = alAsset.thumbnail;
+            UIImage *thumbnailImage = [UIImage imageWithCGImage:thumbnailImageRef scale:2.0 orientation:UIImageOrientationUp];
+            dispatch_async(dispatch_get_main_queue(), ^{
+                if (completion) completion(thumbnailImage,nil,YES);
                 
-                dispatch_async(dispatch_get_main_queue(), ^{
-                    if (completion) completion(fullScrennImage,nil,NO);
-                });
+                if (photoWidth == [UIScreen mainScreen].bounds.size.width) {
+                    dispatch_async(dispatch_get_global_queue(0,0), ^{
+                        ALAssetRepresentation *assetRep = [alAsset defaultRepresentation];
+                        CGImageRef fullScrennImageRef = [assetRep fullScreenImage];
+                        UIImage *fullScrennImage = [UIImage imageWithCGImage:fullScrennImageRef scale:2.0 orientation:UIImageOrientationUp];
+                        
+                        dispatch_async(dispatch_get_main_queue(), ^{
+                            if (completion) completion(fullScrennImage,nil,NO);
+                        });
+                    });
+                }
             });
-        }
+        });
     }
+    return 0;
 }
 
 - (void)getPostImageWithAlbumModel:(TZAlbumModel *)model completion:(void (^)(UIImage *))completion {
@@ -503,6 +523,17 @@
     }
 }
 
+- (NSString *)getAssetIdentifier:(id)asset {
+    if (iOS8Later) {
+        PHAsset *phAsset = (PHAsset *)asset;
+        return phAsset.localIdentifier;
+    } else {
+        ALAsset *alAsset = (ALAsset *)asset;
+        NSURL *assetUrl = [alAsset valueForProperty:ALAssetPropertyAssetURL];
+        return assetUrl.absoluteString;
+    }
+}
+
 #pragma mark - Private Method
 
 - (TZAlbumModel *)modelWithResult:(id)result name:(NSString *)name{

TZImagePickerController/TZImagePickerController/TZPhotoPickerController.m

@@ -592,8 +592,10 @@ static CGSize AssetGridThumbnailSize;
     
     NSMutableArray *assets = [NSMutableArray arrayWithCapacity:indexPaths.count];
     for (NSIndexPath *indexPath in indexPaths) {
-        TZAssetModel *model = _models[indexPath.item];
-        [assets addObject:model.asset];
+        if (indexPath.item < _models.count) {
+            TZAssetModel *model = _models[indexPath.item];
+            [assets addObject:model.asset];
+        }
     }
     
     return assets;