ios - 如何等待完成 dataTaskWithRequest？

Question

如何等待 dataTaskWithRequest 完成？网络抓取完全结束后，我需要执行一些任务。

Answer 1

如果确实需要同步请求，可以使用信号量。

我在 NSURLSession 上实现了一个小类来提供这个功能。

在.h文件中:

@import Foundation.NSURLSession;

@interface NSURLSession (Additions)

+ (NSData *)sendSynchronousRequest:(NSURLRequest *)request returningResponse:(NSURLResponse **)response error:(NSError **)error;

@end

在.m文件中:

@implementation NSURLSession (Additions)

+ (NSData *)sendSynchronousRequest:(NSURLRequest *)request returningResponse:(NSURLResponse *__autoreleasing *)responsePointer error:(NSError *__autoreleasing *)errorPointer
{
    dispatch_semaphore_t semaphore;
    __block NSData *result = nil;

    semaphore = dispatch_semaphore_create(0);

    void (^completionHandler)(NSData * __nullable data, NSURLResponse * __nullable response, NSError * __nullable error);
    completionHandler = ^(NSData * __nullable data, NSURLResponse * __nullable response, NSError * __nullable error)
    {
        if ( errorPointer != NULL )
        {
            *errorPointer = error;
        }

        if ( responsePointer != NULL )
        {
            *responsePointer = response;
        }

        if ( error == nil )
        {
            result = data;
        }

        dispatch_semaphore_signal(semaphore);
    };

    [[[NSURLSession sharedSession] dataTaskWithRequest:request completionHandler:completionHandler] resume];

    dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);

    return result;
}

@end