Question

我有一个程序，我目前直接下载3个不同的URL，我想修改它，以便我可以异步下载网页，但我希望所有3个网页下载都在程序之前完成进展。我在网上看过教程，但我仍然无法让NSOperation和NSoperationqueue工作。

这是我创建的NSOperation课程

#import <Foundation/Foundation.h>

@interface LoadPage : NSOperation

@property (nonatomic, copy) NSURL *URL;
@property (nonatomic, copy) NSData *webpage;

- (id)initWithURL:(NSURL*)url;
- (void)main;

@end

它只是为了下载网页而设计的

#import "LoadPage.h"
//Loadpage.m
@implementation LoadPage
@synthesize URL;
@synthesize webpage;

- (id)initWithURL:(NSURL*)url{
    [self setURL:url];
    return self;
}
//Download Webpage function
- (void)main {
    NSData *page = [NSData dataWithContentsOfURL:URL];
    [self setWebpage:page];
}

我想下载3个单独的网页，并同时完成所有这3个网页，并在完成后继续执行程序的其余部分。

@interface MasterParser : NSObject{
    NSOperationQueue *queue;
}

-(NSMutableArray *)loadPlayer:(NSString *)name;

@end

@implementation MasterParser
    -(NSMutableArray *)parsePage:(NSString *)name{
        NSURL *google = [NSURL URLWithString:@"http://www.Google.com"];
        NSURL *yahoo = [NSURL URLWithString:@"http://www.yahoo.com"];
        NSURL *mlbtraderumors = [NSURL URLWithString:@"http://www.mlbtraderumors.com"];

        LoadPage *gpage = [[LoadPage alloc] initWithURL:google];
        LoadPage *ypage = [[LoadPage alloc] initWithURL:yahoo];
        LoadPage *mpage = [[LoadPage alloc] initWithURL:mlbtraderumors];

        queue = [[NSOperationQueue alloc] init];
        [queue addOperation:gpage]; 
        [queue addOperation:ypage];
        [queue addOperation:mpage];

        [queue waitUnitilAllOperationsAreFinished];

        NSData *webpage = [gpage webpage];
    //...etc do all the operations and parsing with the webpages after all the downloads are done
}

当我运行此程序冻结时，我得到一个错误的执行错误。我的怀疑是我需要在loadpage.m

的末尾使用一行

    [MasterParser performSelectorOnMainThread:@selector(parsePage:)
                                       withObject:nil
                                    waitUntilDone:YES];

任何帮助将不胜感激！

Answer 1

与下载网页相比，解析本身不应该是一个大问题，所以如果你在主线程上执行它不应该创建太多延迟，但如果你愿意，你可以解析单独线程上的网页至。我想指出的另一件事是，如果你要打电话给[MasterParser performSelectorOnMainThread:@selector(parsePage:) withObject:nil waitUntilDone:YES];，这将在主线程上调用+[MasterParser parsePage:nil]。相反它应该是self（或任何对象调用该方法），所以[self performSelectorOnMainThread:@selector(parsePage:) withObject:nil waitUntilDone:YES];

Answer 2

首先，我要感谢所有帮助我回答这个问题的人。关键是添加行

self=[super init];
to the initWithURL method after that everything started working.


#import "LoadPage.h"

@implementation LoadPage
@synthesize URL;
@synthesize webpage;


- (id)initWithURL:(NSURL*)url{
    self = [super init];
    [self setURL:url];
    return self;
}
- (void)main {
    NSData *page = [NSData dataWithContentsOfURL:URL];
    [self setWebpage:page];
}


@end

再次感谢所有帮助回答此问题的人。

NSOperationQueue异步下载网页

2 个答案: