如何在 iPhone 中使用多个代表？

Question

我正在使用下面的代码来使用 json 但我需要在同一页面中更多的 url 连接，如何实现它，提前感谢

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
[responseData setLength:0];
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
[responseData appendData:data];
}

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
NSLog([NSString stringWithFormat:@"Connection failed: %@", [error description]]);
 }

- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
[connection release];
//do something with the json that comes back ... (the fun part)
}

- (void)viewDidLoad
{
[self searchForStuff:@"iPhone"];

}

-(void)searchForStuff:(NSString *)text
 {
responseData = [[NSMutableData data] retain];
NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL   URLWithString:@"http://www.whatever.com/json"]];
[[NSURLConnection alloc] initWithRequest:request delegate:self];
}

我正在使用 php 进行网络访问

Answer 1

不要做任何那样的事情。

相反，使用出色的 ASIHTTPRequest 库，它使一切变得更加简单和更好。从字面上看，自从我几年前发现 ASI 以来，我还没有编写过任何 NSURLConnection，一个也没有。

ASI 的块接口允许您在触发请求对象之前使用其处理程序代码配置请求对象，并且无需任何委派。

__block ASIHTTPRequest *r = [ASIHTTPRequest requestWithUrl:myNSURLObject];
[r setCompletionBlock:^{
    NSLog([r responseString]); //for instance
}];
[r startAsynchronous];

如果块让您感到害怕，您还可以将特定请求指向特定方法，以便可以单独处理不同的请求类型：

- (void) viewDidLoad { //or wherever
    ASIHTTPRequest *r = [ASIHTTPRequest requestWithUrl:myFirstURL];
    r.delegate = self;
    [r setDidFinishSelector:@selector(requestDone:)];
    [r startAsynchronous];
}

// then later on...
- (void)requestDone:(ASIHTTPRequest *)request
{
   NSString *response = [request responseString];
}

Answer 2

您实际上不需要超过一名代表。您需要多个 NSURLConnection，您可以测试看看哪一个正在调用委托方法。

例如。假设以下实例变量（或属性）：

NSURLConnection *connectionA;
NSURLConnection *connectionB;
NSMutableData *dataA;
NSMutalbeData *dataB;

首先实例化每个 NSURLConnection 变量

-(void)searchA:(NSString *)text
{
    NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:[NSString stringWithFormat:@"http://www.a.com/%@", text]]];
    connectionA = [[NSURLConnection alloc] initWithRequest:request delegate:self];
}

-(void)searchB:(NSString *)text
{
    NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:[NSString stringWithFormat:@"http://www.b.com/%@", text]]];
    connectionB = [[NSURLConnection alloc] initWithRequest:request delegate:self];
}

然后您可以测试以查看哪个连接正在调用委托方法并根据连接自定义实现

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
    if (connection == connectionA) {
        [dataA appendData:data];
    }
    else if (connection == connectionB) {
        [dataB appendData:data];
    }
}

您需要为每个委托方法执行此操作。

Answer 3

您可以使用实例变量来保存指向连接的指针。然后在委托回调中，检查指针是否相等，以检查您正在处理哪个连接。

Answer 4

由于 NSValue 符合 NSCopying 规范，我使用它来包装指向连接的指针，并将其用作从 NSMutableDictionary 访问相关数据的密钥。例如，您可能会执行以下操作：

-(void)searchForStuff:(NSString *)text withTarget:(id)target selector:(SEL)selector {
    responseData = [[NSMutableData data] retain];
    NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:@"http://www.whatever.com/json"]];
    NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:target,@"target",NSStringFromSelector(selector),@"selector",nil];
    NSURLConnection *c = [[NSURLConnection alloc] initWithRequest:request delegate:self];
    [myMutableDictionary setObject:options forKey:[NSValue valueWithPointer:c]];
    [c release];
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
    NSValue *p = [NSValue valueWithPointer:connection];
    NSDictionary *options = [myMutableDictionary objectForKey:p];
    if (options) {
        id target = [options objectForKey:@"target"];
        SEL selector = NSSelectorFromString([options objectForKey:@"selector"]);
        if (target && selector && [target respondsToSelector:selector]) {
            [target performSelector:selector withObject:responseData];
        }
    }
}