自定义委托的问题

Question

这是我第一次尝试编写自己的代表。我正在使用 iOS5 Beta 7 并编写我的委托函数。

它应该做的是表（MyTableController）加载电视频道列表。这是一个包含键“logotype”的字典，它是图像标识的 URL。 我创建了名为“Channel”的类和名为“ChannelDelegate”的委托。现在，当我的表执行 cellForRowAtIndexPath 操作时，它会启动我的 Channel 类并调用函数 getChannelImageForChannelId:externalReference:indexPath。到目前为止一切顺利，现在我的通道类检查文件是否在本地存在，如果不存在，它将下载它（使用 ASIHttpRequest）。另外，到目前为止一切都很好。现在，当 ASIHttpRequest 在 requestDidFinish 上返回时，它会在一些结果后消失。我注意到该文件确实被下载了，因为经过几次尝试后它就像一个魅力，因此我的代表似乎可以工作。

这是我的代码：
The CellForRowAtIndexPath:

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *CellIdentifier = @"CurrentChannelInfoCell";

    CurrentChannelInfoCell *cell = (CurrentChannelInfoCell*)[tableView dequeueReusableCellWithIdentifier:CellIdentifier];

    if (cell == nil){
        NSArray *topLevelObjects = [[NSBundle mainBundle] loadNibNamed:CellIdentifier owner:nil options:nil];

        for(id currentObject in topLevelObjects)
        {
            if([currentObject isKindOfClass:[CurrentChannelInfoCell class]])
            {
                cell = (CurrentChannelInfoCell *)currentObject;
                break;
            }
        }
    }


    NSArray *keys = [self.content allKeys];
    id channelId = [keys objectAtIndex:indexPath.row];
    NSDictionary *channel = [self.content objectForKey:channelId];

    int cId = [(NSString*)channelId intValue];

    [cell.textLabel setText:[channel objectForKey:@"name"]];
    [cell.channelImage setHidden:YES];

    Channel *theChannel = [[Channel alloc] init];
    [theChannel setDelegate:self];
    [theChannel getChannelImageForChannelId:cId externalRefference:[channel objectForKey:@"logotype"] indexPath:indexPath];

    return cell;
}

- (void)didRecieveImageForChannel:(NSString*)imagePath indexPath:(NSIndexPath*)indexPath
{
    NSLog(@"Did recieve the it.!");
}

My Delegate, ChannelDelegate.h:

#import <Foundation/Foundation.h>

@class Channel;

@protocol ChannelDelegate <NSObject>

@optional
- (void)didRecieveImageForChannel:(NSString*)imagePath indexPath:(NSIndexPath*)indexPath;

@end

Channel.h:

#import <Foundation/Foundation.h>
#import "ChannelDelegate.h"

#import "Reachability.h"
#import "ASIHTTPRequest.h"
#import "ASINetworkQueue.h"
#import "ASIFormDataRequest.h"

@interface Channel : NSOperation <NSObject, ASIHTTPRequestDelegate>
{   
    ASINetworkQueue *networkQueue;

    // Called on the delegate (if implemented) when the request completes successfully.
    id <ChannelDelegate> delegate;

    SEL didRecieveImageForChannelSelector;
}

@property (strong, nonatomic) id delegate;
@property (assign) SEL didRecieveImageForChannelSelector;

- (void)getChannelImageForChannelId:(int)channelId externalRefference:(NSString*)url indexPath:(NSIndexPath*)indexPath;
- (id)delegate;

@end

Channel.m:

#import "Channel.h"
#import <objc/runtime.h>

@implementation Channel

static char kAssociationKey;

@synthesize didRecieveImageForChannelSelector;
@synthesize delegate;

- (void)getChannelImageForChannelId:(int)channelId externalRefference:(NSString*)url indexPath:(NSIndexPath*)indexPath
{
    [self setDidRecieveImageForChannelSelector:@selector(didRecieveImageForChannel:indexPath:)];

    NSString *documentsPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];

    NSString *imagePath = [documentsPath stringByAppendingPathComponent:[NSString stringWithFormat:@"%d.gif", channelId]];
    BOOL fileExists = [[NSFileManager defaultManager] fileExistsAtPath:imagePath];

    if (fileExists)
    {
        NSLog(@"Downloaded image!");
        [[self delegate] performSelector:[self didRecieveImageForChannelSelector] withObject:imagePath withObject:indexPath];
    }
    else {
        NSLog(@"Need to fetch it.!");

        NSURL *theUrl = [NSURL URLWithString:url];

        ASINetworkQueue *newQueue = [[ASINetworkQueue alloc] init];
        [newQueue setRequestDidFinishSelector:@selector(channelImageFetched:)];
        [newQueue setRequestDidFailSelector:@selector(processFailed:)];
        [newQueue setDelegate:self];

        ASIHTTPRequest *request = [ASIHTTPRequest requestWithURL:theUrl];
        [request setTimeOutSeconds:60];
        [request setDownloadDestinationPath:imagePath];
        [newQueue addOperation:request];

        objc_setAssociatedObject(request, &kAssociationKey, indexPath, OBJC_ASSOCIATION_RETAIN_NONATOMIC);

        [newQueue go];
    }
}

- (id)delegate
{
    id d = delegate;
    return d;
}

- (void)setDelegate:(id)newDelegate
{
    delegate = newDelegate;
}

// Handle process two
- (void)channelImageFetched:(ASIHTTPRequest *)request 
{
    NSLog(@"channelImageFetched!");


    NSIndexPath *indexPath = objc_getAssociatedObject(request, &kAssociationKey);
    NSString *imagePath = request.downloadDestinationPath;

    [[self delegate] performSelector:[self didRecieveImageForChannelSelector] withObject:imagePath withObject:indexPath];    

    NSLog(@"File downloaded!");
}

- (void) processFailed:(ASIHTTPRequest *)request
{   
    NSError *error = [request error];

    UIAlertView *errorView;

    errorView = [[UIAlertView alloc]
                 initWithTitle: NSLocalizedString(@"Whoops!", @"Errors")
                 //              message: NSLocalizedString(@"An error occured while preforming the request. Please try again.", @"Network error")
                 message: [error localizedDescription]
                 delegate: self
                 cancelButtonTitle: NSLocalizedString(@"Close", @"Errors") otherButtonTitles: nil];

    [errorView show];

    /*  NSDictionary *dictionary = [NSDictionary dictionaryWithObjectsAndKeys:
     [request error], @"Error",
     [request url], @"URL",
     [[NSDate alloc] init], @"timestamp", nil];

     [FlurryAPI logEvent:@"APNS-Could not fetch data." withParameters:dictionary timed:YES];
     */
}

@end

我收到的错误似乎有时有所不同，但是这些似乎是我得到的错误：

2011-09-26 13:11:57.605 TVSports[4541:ef03] 完成！
2011-09-26 13:11:57.609 TVSports[4541:ef03] 已下载图像！
2011-09-26 13:11:57.610 TVSports[4541:ef03] 收到了！
2011-09-26 13:11:57.613 TVSports[4541:ef03] 需要获取 如果.!
2011-09-26 13:11:57.616 TVSports[4541:ef03] 需要 获取它。！
2011-09-26 13:11:57.618 TVSports[4541:ef03] 需要获取它。！
2011-09-26 13:11:57.621 TVSports[4541:ef03] 需要获取它。！
2011-09-26 13:11:57.624 TVSports[4541:ef03] 需要获取它。！
2011-09-26 13:11:57.629 TVSports[4541:ef03] 需要获取 它.!
2011-09-26 13:11:57.633 TVSports[4541:ef03] 需要 获取它。！
2011-09-26 13:11:57.663 TVSports[4541:ef03] 需要获取它。！
2011-09-26 13:11:57.669 TVSports[4541:ef03] 需要获取它。！
2011-09-26 13:11:57.846 TVSports[4541:ef03] -[UIDeviceWhiteColor channelImageFetched:]: 无法识别的选择器发送到实例 0x65a1e30
2011-09-26 13:11:57.847 TVSports[4541:ef03] * 由于未捕获的异常而终止应用程序 'NSInvalidArgumentException'，原因：'-[UIDeviceWhiteColor channelImageFetched:]: 无法识别的选择器发送到实例 0x65a1e30'
*第一次抛出调用堆栈：
(0x15da272 0x1769ce6 0x15dbf0d 0x1540e2f 0x1540c12 0x15dc092 0x3adf8 0x15dc092 0x24c43 0x15dc092 0xef9fac 0x15aec0f 0x15118c3 0x15111a4 0x1510b04 0x1510a1b 0x1ce6f67 0x1ce702c 0x608cf2 0x2718 0x2675 0x1)
终止调用抛出 异常（gdb）

或者我在 ASIHTTPRequest 中的一行上得到 EXC_BAD_ACCESS （我无法重现最近 10 次尝试。）

有人能看出我做错了什么吗？我的代码哪里搞砸了？

Answer 1

[UIDeviceWhiteColor channelImageFetched:]: unrecognized Selector sent to instance 0x65a1e30 -- 这告诉您“channelImageFetched”“消息”已“发送”到 UIDeviceWhiteController 类型的对象。 （即，调用了“UIIDeviceWhiteController ->channelImageFetched”。）并且 UIDeviceWhiteController 没有名为“channelImageFetched”的方法。

虽然这可能是您的指针混淆的问题，但更有可能的是确实实现的对象（您的对象） “channelImageFetched”被过度释放和释放（您可以通过在 dealloc 例程中放置 NSLog 来确认这一点。）因此您的问题很可能是一个常见的存储管理错误

。一般来说，当一个对象被传递给一个委托对象时，它应该保留它，直到所有可能的委托方法都被调用，此时第一个对象应该释放该委托对象，但当然它是你的。在将委托对象设置为委托之前，以及在调用所有委托方法之后（如果需要），有责任保留委托对象

[顺便说一句，虽然评论和诊断消息中的一些幽默总是受欢迎的，但使用它是相当不专业的”。妈妈……”在任何您可能会向其他人公开的代码。]

Answer 2

好吧，我仍然不知道发生了什么..但似乎我已经找到了解决方法。

在 mu Channel.m 文件中，我稍微更改了内容。我现在只是在请求对象上执行 startAsynchronous，而不是使用 NetworkQueue。

最终结果：

[...]
    if (fileExists)
    {
        NSLog(@"Downloaded image!");
        [[self delegate] performSelector:[self didRecieveImageForChannelSelector] withObject:imagePath withObject:indexPath];
    }
    else {
        NSLog(@"Need to fetch the image!");

        NSURL *theUrl = [NSURL URLWithString:url];

        ASIHTTPRequest *request = [ASIHTTPRequest requestWithURL:theUrl];
        [request setDidFinishSelector:@selector(channelImageFetched:)];
        [request setDidFailSelector:@selector(processFailed:)];
        [request setTimeOutSeconds:60];
        [request setDownloadDestinationPath:imagePath];

        objc_setAssociatedObject(request, &kAssociationKey, indexPath, OBJC_ASSOCIATION_RETAIN_NONATOMIC);

        [request startAsynchronous];
    }
[...]