Question

我正在尝试运行此代码，但它无法运行。我已经尝试过列出同样问题的其他解决方案，但到目前为止还没有工作。我尝试将一个nslog放在dispatch_async中，但它甚至没有被调用。

- (void)viewDidLoad {
    [super viewDidLoad];
    self.keyboard = [[[NSBundle mainBundle] loadNibNamed:@"Keyboard" owner:nil options:nil] objectAtIndex:0];
    [self addGesturesToKeyboard];
    self.inputView = self.keyboard;
}
- (void)addGesturesToKeyboard {
    [self.keyboard.searchKey addTarget:self action:@selector(pressSearchKey) forControlEvents:UIControlEventTouchUpInside];
}
- (void)pressSearchKey {
    NSInteger numberOfResults = 3;
    NSString *searchString = self.keyboard.textField.text;

    NSString *encodedSearchString = [searchString stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
    NSString *finalSearchString = [NSString stringWithFormat:@"https://itunes.apple.com/lookup?term=%@&entity=song&limit=%ld",searchString,numberOfResults];

    NSURL *searchURL = [NSURL URLWithString:finalSearchString];
    dispatch_queue_t iTunesQueryQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,  kNilOptions);

    dispatch_async(iTunesQueryQueue, ^{
        self.keyboard.firstLabel.text = @"hi";
        NSError *error = nil;
        NSData *data = [NSData dataWithContentsOfURL:searchURL];

        if (data && !error) {
            NSDictionary *JSON = [NSJSONSerialization JSONObjectWithData:data options:0 error:nil];

            self.results = [NSMutableArray array];
            NSArray *resultsArray = [JSON objectForKey:@"results"];
            for (NSDictionary *bpDictionary in resultsArray) {
                // self.keyboard.firstLabel.text = [bpDictionary objectForKey:@"trackName"];
            }  
        }
    });

    [self.keyboard.view1 setHidden:YES];
    [self.keyboard.view2 setHidden:NO];
}

已更新

dispatch_async(iTunesQueryQueue, ^{
        NSError *error = nil;
        NSData *data = [[NSData alloc] initWithContentsOfURL:searchURL options:NSDataReadingUncached error:&error];

        if (data && !error) {
            NSDictionary *JSON = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingMutableContainers error:nil];

            NSArray *array = [JSON objectForKey:@"results"];
            dispatch_async(dispatch_get_main_queue(), ^{
            self.keyboard.firstLabel.text = [array objectAtIndex:0];
            });
        }
    });

Answer 1

除了向队列添加块之外，还需要让系统服务队列。这可以通过在dispatch_main()初始化结束时调用NSApplicationMain()，UIApplicationMain()，main()或类似内容来完成。

示例：

#include <dispatch/dispatch.h>
#include <stdio.h>

int main() {
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        printf("Example\n");
    });

    dispatch_main();
}

此外，为什么要将kNilOptions传递给dispatch_get_global_queue？请传递0。

Dispatch_async未被调用，其中的nslog也不是这样

1 个答案: