Question

我很糟糕我实际上是在外面写这个代码，这是一个很大的错误

我正在学习GCD队列并创建在后台运行的块，

-(IBAction) refresh:(id) sender
{
    dispatch_queue_t downloadQueue = dispatch_queue_create("app data", NULL);
    dispatch_async(downloadQueue, ^{
        //. . . Call a method which download XML file from server . . .
        dispatch_async(dispatch_get_main_queue(), ^{
        //. . . Update UI with dowanloaded data . . .    
        });
    });
    dispatch_release(downloadQueue);
}

但这行代码显示编译错误

dispatch_queue_t downloadQueue = dispatch_queue_create("eiap data", NULL);

错误：初始化元素不是编译时常量

我可以说“app data”是一个错误，我正在创建一个const char，但是我不知道它有什么问题？

由于

Answer 1

如果我这样做，它会编译：

dispatch_queue_t downloadQueue = dispatch_queue_create("app data", NULL);

但如果我这样做，我会得到你提到的错误：

static dispatch_queue_t downloadQueue = dispatch_queue_create("app data", NULL);

我认为你宣称它是静态的。或者你实际上是在方法体之外将其声明为全局变量。

Answer 2

删除初始化字符串中的空格。

使用类似：

dispatch_queue_t downloadQueue = dispatch_queue_create("com.eiap.dataTask", NULL);

Apple建议使用反向DNS表示法样式字符串。

Here's a tutorial you can refer to, b.t.w.我希望我的回答可以帮助你！

Answer 3

尝试使用dispatch_queue_t downloadQueue = dispatch_queue_create(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);

以下是我对您所描述的内容的实现：

UIAlertView *av =[[UIAlertView alloc] initWithTitle:@"Loading Data" message:@"" delegate:self cancelButtonTitle:nil otherButtonTitles:nil];
UIActivityIndicatorView *ActInd=[[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhiteLarge];

[UIApplication sharedApplication].networkActivityIndicatorVisible = YES;

[ActInd startAnimating];
[ActInd setFrame:CGRectMake(125, 60, 37, 37)];
[av addSubview:ActInd];
[av show];

dispatch_queue_t callerQueue = dispatch_get_main_queue();
//dispatch_retain(callerQueue);
dispatch_queue_t downloadQueue = dispatch_queue_create(DISPATCH_QUEUE_PRIORITY_DEFAULT,
                                                       0);

dispatch_async(downloadQueue, ^{
    [self doLoadData];
    dispatch_async(callerQueue, ^{
        [av dismissWithClickedButtonIndex:0 animated:YES];
        [av release];
        [UIApplication sharedApplication].networkActivityIndicatorVisible = NO;
        [self.tableView performSelectorOnMainThread:@selector(reloadData) withObject:nil waitUntilDone:NO];
    });
    dispatch_release(downloadQueue);
});

＆＃34;初始化元素不是编译时常量＆＃34;同时创建GCD队列

3 个答案: