创建GCD队列时“初始化程序元素不是编译时常量”

Question

我的错实际上是在实施之外编写此代码，这真是个天真的错误

我正在学习GCD队列并创建要在后台运行的代码块，

-(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);
}

但是这行代码显示了编译错误

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

错误 ： 初始化程序元素不是编译时常量

---

我可以说我正在动态创建A的“应用数据” const char出了点问题，但是我不知道这是怎么回事？

谢谢

Answer 1

如果执行此操作，它将编译：

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

但是如果这样做，我会得到您提到的错误：

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

我认为您是在声明它为静态。 或者您实际上是在方法主体之外将其声明为全局变量。

Answer 2

摆脱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。

这是您可以参考的教程，希望我的回答对您有所帮助！

Answer 3

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

这是您描述的我的实现：

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);
});