Question

我正在尝试创建NSURLConnection的子类，其中我有一个额外的属性（在本例中为“connectionName”），以帮助我区分两个不同的连接。

我创建了子类，将其命名为CustomURLConnection，并为其赋予了属性“connectionName”。

然后在我的文件ImagesViewController.m（这是一个UICollectionView）我导入标题CustomURLConnection并尝试给连接一个名称并在之后检索它，但它不起作用，因为一旦我进入此集合视图，应用程序崩溃并给我以下错误：

- [NSURLConnection setConnectionName：]：无法识别的选择器发送到实例0x1090a40f0

以下是一些代码:(如果你愿意，这里是CLEARER IMAGE）

CustomURLConnection.h

#import <Foundation/Foundation.h>

@interface CustomURLConnection : NSURLConnection

@property (strong, nonatomic) NSString *connectionName;

@end

ImagesViewController.h

#import <UIKit/UIKit.h>

@interface ImagesViewController : UICollectionViewController<NSURLConnectionDelegate>

@property (strong, nonatomic) UIImageView *imageView;

@end

ImagesViewController.m

...
#import "CustomURLConnection.h"

@interface ImagesViewController (){
    NSArray *contentStrings;
    NSMutableData *contentData; // Holds data from the initial load
    NSMutableData *contentImageData; // Holds data when the user scrolls up/down in the collection view
}
@end

...

-(void)loadInitialData{ // Loads data from page
    NSString *hostStr = @"http://www.website.com/example";
    NSURL *dataURL = [NSURL URLWithString:hostStr];
    NSURLRequest *request = [NSURLRequest requestWithURL:dataURL];
    CustomURLConnection *connectionData = (CustomURLConnection *)[NSURLConnection connectionWithRequest:request delegate:self]; // Make connection
    connectionData.connectionName = @"InitialData"; // Give it a name
}

...

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{
    // Do some stuff

    NSString *hostStr = @"http://www.website.com/example2";

    _imageView = [[UIImageView alloc] initWithFrame:CGRectMake(0,0,100,100)];
    [imageCell addSubview:_imageView]; // Adds an image view to each collection cell

    NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:hostStr]];
    CustomURLConnection *connectionImg = (CustomURLConnection *)[NSURLConnection connectionWithRequest:request delegate:self]; // Make connection
    connectionImg.connectionName = @"ImageData"; // Give it a different name than before

    // Do some stuff
    return imageCell;
}

...

// Here are the main methods for the connections
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response{
    if([((CustomURLConnection *)connection).connectionName isEqualToString:@"InitialData"]){
        contentData = [[NSMutableData alloc] init];
    }
    else{
        contentImageData = [[NSMutableData alloc] init];
    }
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data{
    if([((CustomURLConnection *)connection).connectionName isEqualToString:@"InitialData"]){
        [contentData appendData:data];
    }
    else{
        [contentImageData appendData:data];
    }
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection{
    if([((CustomURLConnection *)connection).connectionName isEqualToString:@"InitialData"]){
        // Do some stuff
    }
    else{
        UIImage *image = [[UIImage alloc] initWithData:contentImageData];
        _imageView.image = image;
    }
}

我错过了什么吗？我之前多次遇到过这个错误，但原因从来都不一样，这次我似乎无法自己找到解决方案。

希望你能看到我做错了什么并帮助我:) 感谢。

编辑：事实证明有更好的方法来实现我的目标，have a look here
再次感谢大家的帮助：）

Answer 1

CustomURLConnection *connectionImg = (CustomURLConnection *)[NSURLConnection connectionWithRequest:request delegate:self]; // Make connection

创建一个NSURLConnection对象。转换为CustomURLConnection不会改变这个对象的类。用

替换该行

CustomURLConnection *connectionImg = [CustomURLConnection connectionWithRequest:request delegate:self]; // Make connection

创建子类的实例。

Answer 2

在您的委托方法中，通过CustomURLConnection更改NSURLConnection，例如：

- (void)connection:(CustomURLConnection *)connection didReceiveResponse:(NSURLResponse *)response

当你创建它时，只需：

CustomURLConnection *connectionImg = [[CustomURLConnection alloc] initWithRequest:request delegate:self];
connectionImg.connectionName = @"ImageData"; // Give it a different name than before

Answer 3

在这一行：

CustomURLConnection *connectionData = (CustomURLConnection *)[NSURLConnection connectionWithRequest:request delegate:self];

您正在创建NSURLConnection的实例，而不是CustomURLConnection。因此，当您将结果转换为CustomURLConnection *时，您对编译器撒谎。

稍后，在运行时，当您尝试使用CustomURLConnection的功能时，您会收到异常，因为您的connection是错误的类类型，并且没有实现该方法。

您需要实例化CustomURLConnection，而不是NSURLConnection。

Answer 4

在此处添加其他好的答案，您的CustomURLConnection类应覆盖+connectionWithRequest:delegate:以返回CustomURLConnection的实例，如下所示：

+(CustomURLConnection*)connectionWithRequest:(NSURLRequest*)request delegate:(id)delegate
{
    return [[CustomURLConnection alloc] initWithRequest:request delegate:delegate];
}

这可以让你使用你拥有的相同风格：

CustomURLConnection *connectionData = [CustomURLConnection connectionWithRequest:request delegate:self]; // Make connection

更重要的是，您的代码的用户（很可能是未来的您）可能会认为向+connectionWithRequest:delegate:发送CustomURLConnection将返回CustomURLConnection的实例。如果没有覆盖，他们将获得NSURLConnection的实例，而这是一个难以发现的错误。

子类NSURLConnection给出错误：发送到实例的无法识别的选择器

4 个答案: