GMSThreadException"原因："必须从主线程调用 API 方法"

Question

我在使用Google API终止应用程序时遇到了此错误，这是由于未被发现的例外GMSThreadException

-(void)drawRoute

{

dispatch_queue_t myQueue = dispatch_queue_create("My Queue",NULL);
dispatch_async(myQueue, ^{
    [self fetchPolylineWithOrigin:origin destination:destination completionHandler:^(GMSPolyline *polyline)
     {
         dispatch_async(dispatch_get_main_queue(), ^{
             // Update the UI
             if(polyline)
                 polyline.map = mapView;
             [UIApplication sharedApplication].networkActivityIndicatorVisible = NO;
         });
     }];
});

}

Answer 1

也要在主线程上使用GMSpath和GMSpolyline，然后它应该起作用。

Answer 2

从您的错误消息中，您似乎只能从主线程调用该API方法，尝试使用：

-(void)drawRoute
{
dispatch_async(dispatch_get_main_queue(), ^{
    [self fetchPolylineWithOrigin:origin destination:destination completionHandler:^(GMSPolyline *polyline)
     {
         // Update the UI
         if(polyline)
             polyline.map = mapView;
         [UIApplication sharedApplication].networkActivityIndicatorVisible = NO;
     }];
});
}

这仍然允许您的代码在消失并执行此操作时继续进行，因为它是异步的，但将其保留在主线程（队列）上。该方法具有完整处理程序的事实表明它本身是异步的，也许您根本不需要在这里进行派遣？

我的赌注是您可以做：

-(void)drawRoute
{
    [self fetchPolylineWithOrigin:origin destination:destination completionHandler:^(GMSPolyline *polyline)
     {
         // Update the UI
         if(polyline)
             polyline.map = mapView;
         [UIApplication sharedApplication].networkActivityIndicatorVisible = NO;
     }];
}

或您以前是否遇到过这种性能问题？

Answer 3

在我的情况下，要求在两个地方使用主线程

一个是...

__block GMSMapView *mapView;
dispatch_async(dispatch_get_main_queue(), ^{
    // Create GMSMapView
    mapView = [GMSMapView mapWithFrame:CGRectMake(1, 1, _subView.frame.size.width-2, _subView.frame.size.height-2) camera:camera];
    mapView.myLocationEnabled = YES;
   [_subView addSubview:mapView];
});

第二个是...

- (void)fetchPolylineWithOrigin:(CLLocation *)origin destination:(CLLocation *)destination completionHandler:(void (^)(GMSPolyline *))completionHandler {
  // Code here ....
   __block GMSPolyline *polyline = nil;
   dispatch_async(dispatch_get_main_queue(), ^{ // Second main
        if ([routesArray count] > 0) {
            NSDictionary *routeDict = [routesArray objectAtIndex:0];
            NSDictionary *routeOverviewPolyline = [routeDict objectForKey:@"overview_polyline"];
            NSString *points = [routeOverviewPolyline objectForKey:@"points"];
            GMSPath *path = [GMSPath pathFromEncodedPath:points];
            polyline = [GMSPolyline polylineWithPath:path];
        }
    });
}