解析加載圖像到UIImageView的iOS版

Question

這裏是我傳遞到現場與圖像數據的代碼：

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath 
{ 
    [super tableView:tableView didSelectRowAtIndexPath:indexPath]; 
    rowNo = indexPath.row; 
    PFUser *currentUser = [PFUser currentUser]; 
    PFQuery *query = [PFQuery queryWithClassName:@"Photo"]; 
    [query whereKey:@"username" equalTo:currentUser.username]; 
    [query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) { 
     _photo = [objects objectAtIndex:rowNo]; 
    }]; 

    [self performSegueWithIdentifier:@"showImageCloseup" sender:self]; 

} 

-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender{ 
    ImageCloseupViewController *destination = [segue destinationViewController]; 
    destination.photoObject = _photo; 
} 

，這裏是用來加載圖像的代碼：

- (void)viewDidLoad 
{ 
    [super viewDidLoad]; 
    PFFile *p = [_photoObject objectForKey:@"photo"]; 
    [p getDataInBackgroundWithBlock:^(NSData *data, NSError *error) { 
     if(!error){ 
      UIImage *image = [UIImage imageWithData:data]; 
      [_imageView setImage:image]; 
     } 
    }]; 

由於某種原因，圖像未加載，爲什麼是這樣？我該如何解決它？

Answer 1

此：

[query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) { 
    _photo = [objects objectAtIndex:rowNo]; 
}]; 

[self performSegueWithIdentifier:@"showImageCloseup" sender:self]; 

需要是：

[query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) { 
    _photo = [objects objectAtIndex:rowNo]; 
    [self performSegueWithIdentifier:@"showImageCloseup" sender:self]; 
}]; 

因爲：

// Runs 1st - executes in background thread stores block, then runs block once it's done 
[query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) { 
    // Runs 3rd - already segued at this point 
    _photo = [objects objectAtIndex:rowNo]; 
}]; 

// Runs 2nd - starts segue 
[self performSegueWithIdentifier:@"showImageCloseup" sender:self]; 

然而，這似乎像有你的設計模式的整體問題。如果您已經有權訪問對象，則不必每次都重新查詢整個數據庫。你有一個引用填充tableView的數組嗎？如果是這樣，這樣的事情：

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath 
{ 
    [super tableView:tableView didSelectRowAtIndexPath:indexPath]; 
    rowNo = indexPath.row; 
    _photo = yourDataArray[indexPath.row]; 
    [self performSegueWithIdentifier:@"showImageCloseup" sender:self]; 

}