Objective-C：将选择器作为参数传递，然后调用它

Question

我正在尝试将选择器作为参数传递并稍后执行。但是当我尝试调用选择器并在控制台中出现下一个错误时，我收到 SIGABRT 错误：

由于未捕获的异常而终止应用程序 'NSInvalidArgumentException'，原因：'-[HttpRequest OnFinishConn:]: 无法识别的选择器发送到实例 0x7834c80'

HttpRequest.h

#import <Foundation/Foundation.h>

@interface HttpRequest : NSObject
{
    @private SEL onEndSel;
    @private NSMutableData* receivedData;
}
-(void) StartRequest:(NSString *) url 
          parameters:(NSString*) params 
            onEndSelector:(SEL) selector;
@end

HttpRequest.m

#import "HttpRequest.h"

@implementation HttpRequest

-(void) StartRequest:(NSString *)url 
          parameters:(NSString*)params
          onEndSelector:(SEL)selector
{
    receivedData = [[NSMutableData alloc] init];
    NSMutableURLRequest *request = 
    [[NSMutableURLRequest alloc] initWithURL:[NSURL URLWithString:url]];
    [request setHTTPMethod:@"POST"];
    [request setHTTPBody:[params dataUsingEncoding:NSUTF8StringEncoding]];
    onEndSel = selector;
    NSURLConnection* conn = [[NSURLConnection alloc] initWithRequest:request delegate:self];


}
-(void) connectionDidFinishLoading:(NSURLConnection*) connection
{
    //NSLog([[NSString alloc] initWithData:receivedData encoding:NSUTF8StringEncoding]);
    [self performSelector:onEndSel withObject:[[NSMutableData alloc] initWithData:receivedData]];
}
-(void) connection:(NSURLConnection *)connection didReceiveData:(NSData *)data{
    [receivedData appendData:data];    
}
@end

AppDelegate.m

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    //self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    // Override point for customization after application launch.
    //self.window.backgroundColor = [UIColor whiteColor];
    HttpRequest* req = [[HttpRequest alloc] init];
    SEL mysel = @selector(OnFinishConn:);
    NSString * url = [[NSString alloc] initWithString:@"http://www.google.es"];
    [req StartRequest:url parameters:@"a" onEndSelector:@selector(OnFinishConn:)];
    [self.window makeKeyAndVisible];

    return YES;
}
-(void)OnFinishConn:(NSMutableData *)data
{
    NSLog([[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding]);
}

我是目标 c 的新手，所以请耐心等待。

Answer 1

这是因为您正在尝试使用 目标-动作模式但未传递目标。我实际上会推荐委托方法，但这里是您的界面应该是什么样子的示例。

@interface HttpRequest : NSObject
{
    @private 
    id onEndTarget; //<- need to know who to send the message to (do not retain)
    SEL onEndSel;
    NSMutableData* receivedData;
}

//Accept the target here
-(void) StartRequest:(NSString *) url 
          parameters:(NSString*) params 
           onEndTarget:(id)target
            onEndSelector:(SEL) selector;

//... implementation

-(void) connectionDidFinishLoading:(NSURLConnection*) connection
{
    [onEndTarget performSelector:onEndSel withObject:[[NSMutableData alloc] initWithData:receivedData]];
}

//...
//Inside App Delegate
[req StartRequest:url parameters:@"a" onEndTarget:self onEndSelector:@selector(OnFinishConn:)];

确保不保留 onEndTarget，因为这可能会创建保留周期。还可以考虑将目标设置为属性，以便如果在连接完成之前对连接进行了某些操作，则它可以不再是委托。

Answer 2

您将选择器发送给 self，但那是在 HttpRequest 中。您尝试调用的选择器位于 AppDelegate 中。因此，您将选择器发送到未实现它的对象。要解决此问题，您不仅应该存储选择器，还应该存储指向选择器应发送到的对象的指针。

Answer 3

请阅读有关 NSInitation 的文档或传递如果您的目标操作系统支持，则将块作为参数。