在swift中以表格视图加载图像加载

Question

在我制作的应用程序中，我需要能够在tableView(_:)函数已创建单元格之后将图像加载到表格单元格。我发现这可以通过线程来完成，但我不完全确定它是如何完成的。

有没有人知道我可以如何在tableView(_:)加载其他单元格后启动单独的线程，以便将图像添加到单元格中，同时保持表格视图中的平滑滚动。

Answer 1

这里是你的研究

http://www.raywenderlich.com/76341/use-nsoperation-nsoperationqueue-swift

检查本教程很好的起点，它展示了如何使用的NSOperation实现自己的目标

我做了这样装载机前面，在OBJ-C，但你可以轻松重写

您可以修改代码以便从文档加载图像。接下来的两个方法从文档目录加载所有资产名称。

-(void) updateData 
{ 
    [self.pendingOperations.downloadQueue addOperationWithBlock:^{ 
     NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); 
     NSString *documentsDirectory = [paths objectAtIndex:0]; 
     NSArray *filePathes = [self recursiveRecordsForResourcesOfType:@[@"png", @"jpeg", @"jpg",@"pdf"] inDirectory:documentsDirectory]; 
     @synchronized (self) { 
      //self.documents = [NSArray arrayWithArray:fileRecords]; 
      self.documents = filePathes; 
      NSLog(@"documents count %@", @([self.documents count])); 
     } 
     dispatch_async(dispatch_get_main_queue(), ^(void){ 
      //Run UI Updates 
      [self.delegate modelDidUpdate:self]; 
     }); 

    }]; 

} 

- (NSArray *)recursiveRecordsForResourcesOfType:(NSArray *)types inDirectory:(NSString *)directoryPath{ 

    NSMutableArray *filePaths = [[NSMutableArray alloc] init]; 

    NSMutableDictionary *typesDic = [NSMutableDictionary dictionary]; 
    for (NSString *type in types) 
     [typesDic setObject:type forKey:type]; 

    // Enumerators are recursive 
    NSDirectoryEnumerator *enumerator = [[NSFileManager defaultManager] enumeratorAtPath:directoryPath]; 

    NSString *filePath; 

    while ((filePath = [enumerator nextObject]) != nil){ 

     // If we have the right type of file, add it to the list 
     // Make sure to prepend the directory path 
     if([typesDic objectForKey:[filePath pathExtension]]){ 
      //[filePaths addObject:[directoryPath stringByAppendingPathComponent:filePath]]; 
      CURFileRecord *record = [CURFileRecord new]; 
      record.filePath =[directoryPath stringByAppendingPathComponent:filePath]; 
      record.fileName = filePath; 
      [filePaths addObject:record]; 
     } 
    } 


    return filePaths; 
} 

然后创建的NSOperation子类，并把它改写：

// 3 
- (void)main { 

    // 4 
    @autoreleasepool { 

     if (self.isCancelled) 
      return; 
     NSData *fileData = [[NSFileManager defaultManager] contentsAtPath:self.fileRecord.filePath]; 
     // self.fileRecord.fileData = fileData; 
     if (self.isCancelled) { 
      fileData = nil; 
      return; 
     } 

     if (fileData) { 
      UIImage *newImage; 
      if ([[self.fileRecord.filePath pathExtension] isEqualToString:@"pdf"]) 
      { 
       CGPDFDocumentRef doc = [CURDocumentViewerUtilities MyGetPDFDocumentRef:fileData]; 
       newImage = [CURDocumentViewerUtilities buildThumbnailImage:doc withSize:CGSizeMake(64, 96)]; 
      } 
      else 
      { 
       newImage = [CURDocumentViewerUtilities makePreviewImageFromData:fileData]; 
      } 
      self.fileRecord.previewImage = newImage; 
     } 
     else { 
      self.fileRecord.failed = YES; 
     } 

     fileData = nil; 

     if (self.isCancelled) 
      return; 

     // 5 
     [(NSObject *)self.delegate performSelectorOnMainThread:@selector(imageDownloaderDidFinish:) withObject:self waitUntilDone:NO]; 

    } 
} 

希望这有助于