使用 Protocol 來重構 (ObjC) @ CocoaHeads Taipei 2017.11.09

1. Using Protocol to
Refactor
邱志強, Green Chiu, iOS Developer.

2. 在 iOS ，提到 Protocol
你會想到什什麼?

3. 繼承 ?

4. Delegation ?

5. 其他 ?

6. Delegation Pattern
• Apple ⼤大量量使⽤用在 CocoaTouch SDK
• UITableView, UICollectionView, UIGestureRecognizer
and so on.
• NSURLSession, StoreKit
• 第三⽅方套件

7. NS-Protocols
• 為了了達到特定⽬目的 archive, copy, enumerate
• NSCopying
• NSCoding
• NSFastEnumeration

8. 繼承
• Objective-C/Swift 不⽀支援多重繼承，但可以實作多個
Protocols
• 我們很習慣使⽤用繼承，⼤大部份了了只是為了了部分的 method
或實作
• 可怕的繼承樹
• 在調整後常出現 ”驚喜”

9. Protocol in Objective-C
@protocol SampleProtocol <NSObject>
- (void)sampleMethodA;
- (void)sampleMethodB;
@optional
- (void)sampleOptionalMethod;
@end

10. Protocol 讓⼀一個 class 或
method 知道如何操作物件

11. The End

12. 重構
• 類似/同樣的程式碼重複出現

13. Class LocalPlaylistInfo
- (void)fetchPlaylistCoverImageWithSize …
{
if (…) {
…
UIImage *image = nil;
DBMetaReference *ref = … ;
if (ref.sourceType == …) {
DBMetaItem *item = …;
…
}
else if (ref.sourceType == …) {
MPMediaItem *item = …;
image = [item.artwork imageWith …];
}
else if (ref.sourceType == LocalDBContextSongSourceTypeStore) {
DBMetaItem *item = …;
if (!item) {
return;
}
NSString *imageFileURLString = …;
void (^imageCallback)(NSString *fileURLString, UIImage *image) = ^(NSString *fileURLString, UIImage *image)
{
if (image …) {
}
else if ([NSURL URLWithString:item.photoURL]) {
[[KKRadioImageManager sharedImageManager] fetchImageWithURL:… requester:nil callback:^(UIImage
*receiveImage, NSError *error) {
if (receiveImage) {
…
}
}];
}
};
…

14. Class SongInfoViewModel
- (void)loadSongInfo:(LocalSongInfo *)inSongInfo {
if (inSongInfo.type == LocalDBContextSongSourceTypeStore || ...) {
DBMetaItem *item = inSongInfo.rawItem;
if (inSongInfo.type == LocalDBContextSongSourceTypeStore) {
}
else { … }
self.imageFileURLString = …;
void (^imageCallback)(NSString *fileURLString, UIImage *image) = ^void(NSString
*fileURLString, UIImage *image){
if (image) {
…
weakSelf.albumCoverImage = cropImage;
}
else if ([NSURL URLWithString:item.photoURL]) {
[[KKRadioImageManager sharedImageManager] fetchImageWithURL:… requester:nil
callback:^(UIImage *receiveImage, NSError *error) {
if (receiveImage) {
weakSelf.albumCoverImage = …
}
…
}];
}
…
};
…
return;
}
if (inSongInfo.image) {
…
}
…

15. Issues
• 相似的實作出現在多個地⽅方
• 為了了圖片，View or Model 載入了了很多 classes/framework

16. Design Protocol
typedef NS_ENUM(NSInteger, ProvideImageWay) {
ProvideImageWayNone = NSNotFound,
ProvideImageWayFetchWithURLString = 0,
ProvideImageWayGetWithSize,
ProvideImageWayGenerateWithCallback
};
@protocol LocalItemImageProvider <NSObject>
- (ProvideImageWay)getCoverImageWay;
- (NSString *)coverURLString;
- (UIImage *)coverImageWithSize:(CGSize)inSize;
- (void)generateImageWithCallback:(void(^)(UIImage *))inCallback;
@end

17. After implemented
- (void)loadSongInfo:(LocalSongInfo *)inSongInfo
{
switch ([inSongInfo getCoverImageWay]) {
case UPProvideImageWayGetWithSize:
self.albumCoverImageView.image = [inSongInfo coverImageWithSize:CGSizeMake(…)];
break;
case UPProvideImageWayGenerateWithCallback: {
__weak typeof(self) weakSelf = self;
[inSongInfo generateImageWithCallback:^(UIImage *image) {
weakSelf.albumCoverImageView.image = image;
}];
break;
}
case UPProvideImageWayFetchWithURLString:
…
break;
case UPProvideImageWayNone:
…
break;
}
…
}

18. Optimized
// UIImageView+LocalItemImageProvider.m
- (void)loadImageWithImageProvider:(id<LocalItemImageProvider>)inImageProvider
{
if (![inImageProvider conformsToProtocol:@protocol(LocalItemImageProvider)]) {
return;
}
switch ([inImageProvider getCoverImageWay]) {
case ProvideImageWayGetWithSize:
self.image = [inImageProvider coverImageWithSize:CGSizeMake(44, 44)];
break;
case ProvideImageWayGenerateWithCallback: {
__weak typeof(self) weakSelf = self;
[inImageProvider generateImageWithCallback:^(UIImage *image) {
weakSelf.image = image;
}];
break;
}
case ProvideImageWayFetchWithURLString:
[self fetchImageWithURLString:[inImageProvider coverURLString]];
break;
case ProvideImageWayNone:
default:
…
break;
}
}

19. Finally
- (void)loadSongInfo:(UPLocalSongInfo *)inSongInfo
{
[self.albumCoverImageView loadImageWithImageProvider:inSongInfo];
…
}

20. Besides
• 使⽤用 Protocol 讓程式更更容易易被測試
• Mock 物件變得容易易

21. Testing
// UIImageView+LocalItemImageProvider.m
- (void)loadImageWithImageProvider:(id<LocalItemImageProvider>)inImageProvider
{
if (![inImageProvider conformsToProtocol:@protocol(LocalItemImageProvider)]) {
return;
}
switch ([inImageProvider getCoverImageWay]) {
case ProvideImageWayGetWithSize:
self.image = [inImageProvider coverImageWithSize:CGSizeMake(44, 44)];
break;
case ProvideImageWayGenerateWithCallback: {
__weak typeof(self) weakSelf = self;
[inImageProvider generateImageWithCallback:^(UIImage *image) {
weakSelf.image = image;
}];
break;
}
case ProvideImageWayFetchWithURLString:
[self fetchImageWithURLString:[inImageProvider coverURLString]];
break;
case ProvideImageWayNone:
default:
…
break;
}
}

22. Testing
@interface TCDummyLocalImageProvider: NSObject <LocalItemImageProvider>
- (instancetype)initWithType:(ProvideImageWay)inWay;
@end
@implementation TCDummyLocalImageProvider {
ProvideImageWay way;
}
- (instancetype)initWithType:(ProvideImageWay)inWay
{
self = [super init];
if (self) {
way = inWay;
}
return self;
}
- (ProvideImageWay)getCoverImageWay
{
return way;
}
...
@end

23. Testing
- (void)testUIImageLoadImageWithImageProvider
{
UIImageView *imageView = [[UIImageView alloc] init];
[imageView loadImageWithImageProvider:[NSObject new]];
[imageView loadImageWithImageProvider:[[TCDummyLocalImageProvider alloc]
initWithWay:-1000]];
[imageView loadImageWithImageProvider:[[TCDummyLocalImageProvider alloc]
initWithWay:ProvideImageWayGetWithSize]];
[imageView loadImageWithImageProvider:[[TCDummyLocalImageProvider alloc] initWithWay:...]];
}

24. This is
Protocol-Oriented Programming

25. One more thing…

27. We are hiring
iOS Developer and others

28. Thanks