视频播放器封装支持下载、缓存

我们实现了AVAssetResourceLoaderDelegate协议来拦截视频加载请求，并将其缓存起来。通过在resourceLoader:shouldWaitForLoadingOfRequestedResource:方法中处理请求，我们可以检查是否已经存在缓存数据，如果是，则直接使用缓存数据，否则发起下载请求。

在startDataRequest方法中，我们使用NSURLSessionDataTask来异步下载视频数据，并在下载完成后// Player.h

import <UIKit/UIKit.h>

import <AVFoundation/AVFoundation.h>

@interface Player : NSObject<AVAssetResourceLoaderDelegate>

@property (nonatomic, strong) NSURL *videoURL;
@property (nonatomic, strong) AVPlayer *player;
@property (nonatomic, strong) AVPlayerLayer *playerLayer;

(instancetype)initWithVideoURL:(NSURL*)videoURL;
(void)play;
(void)pause;
(void)stop;
(void)downloadVideoWithCompletion:(void (^)(BOOL success, NSError *error))completion;

@end

// Player.m

import "Player.h"

@implementation Player {
AVAssetResourceLoadingRequest *_loadingRequest;
NSMutableData *_cachedData;
}

(instancetype)initWithVideoURL:(NSURL*)videoURL {
self = [super init];
if (self) {
self.videoURL = videoURL;
[self setupPlayer];
}
return self;
}
(void)setupPlayer {
AVURLAsset asset = [AVURLAsset URLAssetWithURL:self.videoURL options:nil];
[asset.resourceLoader setDelegate:self queue:dispatch_get_main_queue()];
AVPlayerItem playerItem = [AVPlayerItem playerItemWithAsset:asset];
self.player = [AVPlayer playerWithPlayerItem:playerItem];
self.playerLayer = [AVPlayerLayer playerLayerWithPlayer:self.player];
self.playerLayer.videoGravity = AVLayerVideoGravityResizeAspect;
}
(void)play {
[self.player play];
}
(void)pause {
[self.player pause];
}
(void)stop {
[self.player pause];
[self.player seekToTime:kCMTimeZero];
}
(void)downloadVideoWithCompletion:(void (^)(BOOL success, NSError *error))completion {
NSURLSession *session = [NSURLSession sharedSession];
NSURLSessionDownloadTask *downloadTask = [session downloadTaskWithURL:self.videoURL completionHandler:^(NSURL * _Nullable location, NSURLResponse * _Nullable response, NSError * _Nullable error) {
if (error) {
completion(NO, error);
} else {
NSString *documentDirectory = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES).firstObject;
NSString *destinationPath = [documentDirectory stringByAppendingPathComponent:@"downloadedVideo.mp4"];
NSURL *destinationURL = [NSURL fileURLWithPath:destinationPath];
```
      NSError *moveError = nil;
      [[NSFileManager defaultManager] moveItemAtURL:location toURL:destinationURL error:&moveError];
      
      if (moveError) {
          completion(NO, moveError);
      } else {
          completion(YES, nil);
      }
  }
```
}];
[downloadTask resume];
}

pragma mark - AVAssetResourceLoaderDelegate

(BOOL)resourceLoader:(AVAssetResourceLoader *)resourceLoader shouldWaitForLoadingOfRequestedResource:(AVAssetResourceLoadingRequest *)loadingRequest {
if (!_loadingRequest) {
NSURLComponents *urlComponents = [[NSURLComponents alloc] initWithURL:self.videoURL resolvingAgainstBaseURL:NO];
urlComponents.scheme = @"cached";
NSURL *customURL = [urlComponents URL];
```
  if (customURL && _cachedData) {
      NSData *requestedData = [_cachedData copy];
      [self processRequest:loadingRequest withCachedData:requestedData];
      return YES;
  } else {
      _loadingRequest = loadingRequest;
      [self startDataRequest];
  }
```
} else {
// Another loading request is already in progress, so we cannot process the new request concurrently
[loadingRequest finishLoadingWithError:[NSError errorWithDomain:NSURLErrorDomain code:NSURLErrorCancelled userInfo:nil]];
return YES;
}
return YES;
}
(void)startDataRequest {
NSURLSession *session = [NSURLSession sharedSession];
NSURLSessionDataTask *dataTask = [session dataTaskWithURL:self.videoURL completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
if (error) {
[_loadingRequest finishLoadingWithError:error];
} else {
[_loadingRequest
dataRequestDidReceiveResponse:[[NSHTTPURLResponse alloc] initWithURL:_loadingRequest.request.URL statusCode:200 HTTPVersion:@"HTTP/1.1" headerFields:response.allHeaderFields]];
[_loadingRequest.dataRequest
respondWithData:data];
[_loadingRequest finishLoading];
_loadingRequest = nil;
```
      // Cache the loaded data
      _cachedData = [NSMutableData dataWithData:data];
  }
```
}];
[dataTask resume];
}
(void)processRequest:(AVAssetResourceLoadingRequest *)loadingRequest withCachedData:(NSData *)cachedData {
[loadingRequest
dataRequestDidReceiveResponse:[[NSHTTPURLResponse alloc] initWithURL:loadingRequest.request.URL statusCode:200 HTTPVersion:@"HTTP/1.1" headerFields:nil]];

NSUInteger offset = (NSUInteger)loadingRequest.dataRequest.requestedOffset;
NSUInteger length = (NSUInteger)loadingRequest.dataRequest.requestedLength;
NSRange requestedRange = NSMakeRange(offset, length);
NSData *requestedData = [cachedData subdataWithRange:requestedRange];

[loadingRequest.dataRequest respondWithData:requestedData];
[loadingRequest finishLoading];
}