Ios CATextLayer仅在一段时间后显示其内容

我知道这听起来很奇怪，但问题恰恰在于：我有一个

ViewController

，它加载一个与grandcentraldispatch异步的CSV文件（该文件表示一个直方图）。我还有一个名为

historogramview

的自定义视图。当控制器加载完CSV文件后，它调用

historogramview

上的函数

invalidate

。在该函数中，视图解析从文件读取的数据并创建：

有些图层表示直方图中的条形

某些CATextLayer表示条形图的标签

对于形状层没有问题，所有的工作都很好。文本层出现问题：最初只显示背景。文本仅在几秒钟后出现：-/这很奇怪。这是

invalidate

函数的代码（正如我所说，这个函数位于自定义视图中）

---

好的，我明白了。我要感谢rdelmar，他的建议为我指出了问题所在。正如他所说，

invalidate

不是从主线程调用的，而是从后台线程（读取文件的线程）调用的。这是错误的，因为视图必须从主线程更新。因此，我只需通过以下方式调用

invalidate

方法即可解决此问题：

-(void)readCSVFile:(dispatch_io_t)ch{

    //the string that represents the content of CSV file
    NSMutableString __block *stringFromData;

    //read the whole file
    dispatch_io_read(ch, 0, SIZE_MAX, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^(bool done, dispatch_data_t dataRead, int error) {

        if(!error && !done){

            //convert from dispatch_data_t to NSString
            size_t dataSize = dispatch_data_get_size(dataRead);
            stringFromData = [[NSMutableString alloc]initWithCapacity:dataSize];
            dispatch_data_apply(dataRead, ^bool(dispatch_data_t region, size_t offset, const void *buffer, size_t size) {
                [stringFromData appendFormat:@"%.*s", (unsigned int)size, buffer];
                return true;
            });
        }else{
            dispatch_io_close(ch, 0);
            data = [stringFromData componentsSeparatedByCharactersInSet:
                       [NSCharacterSet characterSetWithCharactersInString:@"\n,"]];

            //HERE IS THE SOLUTION
            [[NSOperationQueue mainQueue]addOperationWithBlock:^{
                [self.histogramView invalidate];
            }];
        }

    });
}

---

正在主线程上调用invalidate吗？嗯。。。实际上不是。因为我传递给视图的数据是从异步文件读取加载的（感谢Grand Central Dispatch）。我在分派io读取结束时执行的代码块中调用“invalidate”。检查我的编辑。这是个问题吗？谢谢你的帮助！

- (void)viewDidLoad {
    [super viewDidLoad];

    //create the channel with which read the CSV file
    dispatch_io_t ch = dispatch_io_create_with_path(DISPATCH_IO_STREAM, [[[NSBundle mainBundle] pathForResource:@"histogram1" ofType:@"csv"] UTF8String], O_RDONLY, 0, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), nil);

    //read the CSV file async with GCD
    [self readCSVFile:ch];

    //set the delegates for the histogram view
    self.histogramView.delegate = self;
    self.histogramView.dataSource = self;
}

-(void)readCSVFile:(dispatch_io_t)ch{

    //the string that represents the content of CSV file
    NSMutableString __block *stringFromData;

    //read the whole file
    dispatch_io_read(ch, 0, SIZE_MAX, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^(bool done, dispatch_data_t dataRead, int error) {

        if(!error && !done){

            //convert from dispatch_data_t to NSString
            size_t dataSize = dispatch_data_get_size(dataRead);
            stringFromData = [[NSMutableString alloc]initWithCapacity:dataSize];
            dispatch_data_apply(dataRead, ^bool(dispatch_data_t region, size_t offset, const void *buffer, size_t size) {
                [stringFromData appendFormat:@"%.*s", (unsigned int)size, buffer];
                return true;
            });
        }else{
            dispatch_io_close(ch, 0);
            data = [stringFromData componentsSeparatedByCharactersInSet:
                       [NSCharacterSet characterSetWithCharactersInString:@"\n,"]];

            //AND NOW I CALL INVALIDATE ON THE VIEW
            [self.histogramView invalidate];
        }

    });
}

-(void)readCSVFile:(dispatch_io_t)ch{

    //the string that represents the content of CSV file
    NSMutableString __block *stringFromData;

    //read the whole file
    dispatch_io_read(ch, 0, SIZE_MAX, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^(bool done, dispatch_data_t dataRead, int error) {

        if(!error && !done){

            //convert from dispatch_data_t to NSString
            size_t dataSize = dispatch_data_get_size(dataRead);
            stringFromData = [[NSMutableString alloc]initWithCapacity:dataSize];
            dispatch_data_apply(dataRead, ^bool(dispatch_data_t region, size_t offset, const void *buffer, size_t size) {
                [stringFromData appendFormat:@"%.*s", (unsigned int)size, buffer];
                return true;
            });
        }else{
            dispatch_io_close(ch, 0);
            data = [stringFromData componentsSeparatedByCharactersInSet:
                       [NSCharacterSet characterSetWithCharactersInString:@"\n,"]];

            //HERE IS THE SOLUTION
            [[NSOperationQueue mainQueue]addOperationWithBlock:^{
                [self.histogramView invalidate];
            }];
        }

    });
}