Question

我正在使用此问题NSURLConnection download large file (>40MB)中的代码下载KML文件，并使用Apple的KMLViewer将数据加载到我的MKMap中.KML文件小于<200KB，因此KMLViewer很好。提供的代码在问题应该是很好的事实，当我点击按钮（应该发出网址的请求，然后在地图中加载数据）时，地图只会到达位置0,0，变焦非常大，所以全部我看到的是黑色地图。出了什么问题？我该怎么办？这是代码：（顺便说一下，我有两个连接，因为一个使用JSON从UIsearchBar获取位置的Google搜索结果。）

编辑1

//In the ViewController.m
-(void) searchCoordinatesForAddress:(NSString *)inAddress //for Google location search
{
NSMutableString *urlString = [NSMutableString stringWithFormat:@"http://maps.google.com/maps/geo?q=%@?output=json",inAddress];

[urlString setString:[urlString stringByReplacingOccurrencesOfString:@" " withString:@"+"]];

NSURL *url = [NSURL URLWithString:urlString];

NSURLRequest *request = [[NSURLRequest alloc] initWithURL:url];
NSURLConnection *connection = [[NSURLConnection alloc] initWithRequest:request delegate:self];

[connection release];
[request release];
}


-(void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
[webData setLength:0]; //webData in the header file
}

-(void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
if ( connection = theConnection ) //theConnection is created before
{
[webData appendData:data];
}
NSString *jsonString = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];

NSDictionary *results = [jsonString JSONValue];

NSArray *placemark = [results objectForKey:@"Placemark"];
NSArray *coordinates = [[placemark objectAtIndex:0] valueForKeyPath:@"Point.coordinates"];

double longitude = [[coordinates objectAtIndex:0] doubleValue];
double latitude = [[coordinates objectAtIndex:1] doubleValue];

NSLog(@"Latitude - Longitude: %f %f", latitude, longitude);

[self zoomMapAndCenterAtLatitude:latitude andLongitude:longitude];

[jsonString release];

}

-(void)connectionDidFinishLoading:(NSURLConnection *)connection {

NSString *fileName = [[[NSURL URLWithString:kmlStr] path] lastPathComponent];
NSArray *pathArr = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *folder = [pathArr objectAtIndex:0];

NSString *filePath = [folder stringByAppendingPathComponent:fileName];
NSURL *fileURL = [NSURL fileURLWithPath:filePath];  

NSError *writeError = nil;

[webData writeToURL: fileURL options:0 error:&writeError];
if( writeError) {
    NSLog(@" Error in writing file %@' : \n %@ ", filePath , writeError );
    return;
}
NSLog(@"%@",fileURL);
}

-(void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Error !" message:@"Error has occured, please verify internet connection.."  delegate:nil cancelButtonTitle:@"Ok" otherButtonTitles:nil];

[alert show];
[alert release];
}

-(IBAction)showKmlData:(id)sender
{
NSString *path = [[NSBundle mainBundle] pathForResource:@"KMLGenerator" ofType:@"kml"];

kml = [[KMLParser parseKMLAtPath:path] retain];

NSArray *overlays = [kml overlays];
[mapview addOverlays:overlays];

NSArray *annotations = [kml points];
[mapview addAnnotations:annotations];

MKMapRect flyTo = MKMapRectNull;
for (id <MKOverlay> overlay in overlays) {
    if (MKMapRectIsNull(flyTo)) {
        flyTo = [overlay boundingMapRect];
    } else {
        flyTo = MKMapRectUnion(flyTo, [overlay boundingMapRect]);
    }
}

for (id <MKAnnotation> annotation in annotations) {
    MKMapPoint annotationPoint = MKMapPointForCoordinate(annotation.coordinate);
    MKMapRect pointRect = MKMapRectMake(annotationPoint.x, annotationPoint.y, 0, 0);
    if (MKMapRectIsNull(flyTo)) {
        flyTo = pointRect;
    } else {
        flyTo = MKMapRectUnion(flyTo, pointRect);
    }
}

mapview.visibleMapRect = flyTo;
}

编辑2 我做了修改，现在它没有去任何地方，它崩溃了，因为它找不到KMLGenerator.kml文件（路径）

-(void)showData 
{

NSString *url = /*kmlStr;*/@"http://www.ikub.al/hartav2/handlers/kmlgenerator.ashx?layerid=fc77a5e6-5985-4dd1-9309-f026d7349064&kml=1";
NSURL *path = [NSURL URLWithString:url];
NSURLRequest *request = [[NSURLRequest alloc] initWithURL:path];
NSURLConnection *connection = [[NSURLConnection alloc] initWithRequest:request delegate:self];
theConnection = connection;
[connection release];
[request release];

}

//Search Coordinates for address entered in the searchBar
-(void) searchCoordinatesForAddress:(NSString *)inAddress
{
NSMutableString *urlString = [NSMutableString stringWithFormat:@"http://maps.google.com/maps/geo?q=%@?output=json",inAddress];

[urlString setString:[urlString stringByReplacingOccurrencesOfString:@" " withString:@"+"]];

NSURL *url = [NSURL URLWithString:urlString];

NSURLRequest *request = [[NSURLRequest alloc] initWithURL:url];
NSURLConnection *connection = [[NSURLConnection alloc] initWithRequest:request delegate:self];

[connection release];
[request release];
}

-(void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
[webData setLength:0]; //Here i get an alert: NSData may not respond to -setLength
                           //webData is a NSData object.
}


-(void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
    [webData appendData:data]; //Here i get an alert: NSData may not respond to -appendData
}

-(void)connectionDidFinishLoading:(NSURLConnection *)connection {
    if ( connection == theConnection ) //"theConnection" is for kml file download
    {
        NSString *fileName = [[[NSURL URLWithString:kmlStr] path] lastPathComponent];
        NSArray *pathArr = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
        NSString *folder = [pathArr objectAtIndex:0];

        NSString *filePath = [folder stringByAppendingPathComponent:fileName];
        NSURL *fileURL = [NSURL fileURLWithPath:filePath];  

        NSError *writeError = nil;

        [webData writeToURL: fileURL options:0 error:&writeError];

        if( writeError) {
            NSLog(@" Error in writing file %@' : \n %@ ", filePath , writeError );
            return;
        }

        NSLog(@"%@",fileURL);
    }
    else //it's a geocoding result
    {
        NSString *jsonString = [[NSString alloc] initWithData:webData encoding:NSUTF8StringEncoding];

        NSDictionary *results = [jsonString JSONValue];

        //check the Google geocode error code before looking for coordinates...        
        NSDictionary *statusDict = [results objectForKey:@"Status"];
        NSNumber *errorCode = [statusDict objectForKey:@"code"];
        if ([errorCode intValue] == 200)  //200 is "success"
        {
            NSArray *placemark = [results objectForKey:@"Placemark"];
            NSArray *coordinates = [[placemark objectAtIndex:0] valueForKeyPath:@"Point.coordinates"];

            double longitude = [[coordinates objectAtIndex:0] doubleValue];
            double latitude = [[coordinates objectAtIndex:1] doubleValue];

            NSLog(@"Latitude - Longitude: %f %f", latitude, longitude);

            [self zoomMapAndCenterAtLatitude:latitude andLongitude:longitude];
        }
        else
        {
            NSLog(@"geocoding error %@", errorCode);
        }

        [jsonString release];
    }
}

-(void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Error!" message:@"Error has occured, please verify internet connection..." delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];
[alert show];
[alert release];
}


- (IBAction)showKmlData:(id)sender
{

NSString *path = [[NSBundle mainBundle] pathForResource:@"KMLGenerator" ofType:@"kml"];

kml = [[KMLParser parseKMLAtPath:path] retain];

NSArray *annotationsImmut = [kml points];
NSMutableArray *annotations = [annotationsImmut mutableCopy];
//[mapview addAnnotations:annotations];
[self filterAnnotations:annotations];

MKMapRect flyTo = MKMapRectNull;

for (id <MKAnnotation> annotation in annotations) {
    MKMapPoint annotationPoint = MKMapPointForCoordinate(annotation.coordinate);
    MKMapRect pointRect = MKMapRectMake(annotationPoint.x, annotationPoint.y, 0, 0);
    if (MKMapRectIsNull(flyTo)) {
        flyTo = pointRect;
    } else {
        flyTo = MKMapRectUnion(flyTo, pointRect);
    }
}

mapview.visibleMapRect = flyTo;
}

Answer 1

仍然难以查明原因，但您发布的代码存在一些问题。

首先，在didReceiveData中，这一行可能不是你想要的：

if ( connection = theConnection ) //theConnection is created before

单个=正在进行赋值而不是等式检查（==）。

但是，修复它不是解决方案（另一个问题出在connectionDidFinishLoading）。

didReceiveData方法不是处理地理编码JSON结果的正确位置。对于单个url请求，可以多次调用didReceiveData方法。因此，地理编码结果（就像kml文件一样）可能会以多个块传递，而这些块无法在该方法中单独处理。该方法中的data可能是完整结果的部分流，对于处理没有意义。您应该只将数据附加到NSMutableData对象，或者作为链接问题建议的答案，将数据写入文件。

只能使用connectionDidFinishLoading方法处理/解析数据。

由于您对kml文件下载和地理编码使用相同的连接委托，因此它们都调用相同的connectionDidFinishLoading方法。在该方法中，您不会检查要为其调用哪个连接。

当地理编码网址请求完成并调用connectionDidFinishLoading时，该方法会获取webData中的任何内容（可能是地理编码结果或空数据）并将其写入kmlStr文件。这可能是导致kml数据显示“无”的原因。

您必须将地理编码结果的处理移至connectionDidFinishLoading并检查其中正在调用的连接。

例如：

-(void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
    [webData appendData:data];
}

-(void)connectionDidFinishLoading:(NSURLConnection *)connection {
    if ( connection == theConnection ) //"theConnection" is for kml file download
    {
        NSString *fileName = [[[NSURL URLWithString:kmlStr] path] lastPathComponent];
        NSArray *pathArr = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
        NSString *folder = [pathArr objectAtIndex:0];

        NSString *filePath = [folder stringByAppendingPathComponent:fileName];
        NSURL *fileURL = [NSURL fileURLWithPath:filePath];  

        NSError *writeError = nil;

        [webData writeToURL: fileURL options:0 error:&writeError];
        if( writeError) {
            NSLog(@" Error in writing file %@' : \n %@ ", filePath , writeError );
            return;
        }
        NSLog(@"%@",fileURL);
    }
    else //it's a geocoding result
    {
        NSString *jsonString = [[NSString alloc] initWithData:webData encoding:NSUTF8StringEncoding];

        NSDictionary *results = [jsonString JSONValue];

        //check the Google geocode error code before looking for coordinates...        
        NSDictionary *statusDict = [results objectForKey:@"Status"];
        NSNumber *errorCode = [statusDict objectForKey:@"code"];
        if ([errorCode intValue] == 200)  //200 is "success"
        {
            NSArray *placemark = [results objectForKey:@"Placemark"];
            NSArray *coordinates = [[placemark objectAtIndex:0] valueForKeyPath:@"Point.coordinates"];

            double longitude = [[coordinates objectAtIndex:0] doubleValue];
            double latitude = [[coordinates objectAtIndex:1] doubleValue];

            NSLog(@"Latitude - Longitude: %f %f", latitude, longitude);

            [self zoomMapAndCenterAtLatitude:latitude andLongitude:longitude];
        }
        else
        {
            NSLog(@"geocoding error %@", errorCode);
        }

        [jsonString release];
    }
}

（避免为多个连接使用相同的委托可能会更好。将地理编码移出到具有自己的连接对象和委托方法的另一个类会更加清晰。顺便说一下，iOS5内置了地理编码，所以你不需要自己这样做。请参阅CLGeocoder课程。）

我添加了对Google错误代码的检查。查询的地址可能无法返回结果，在这种情况下将没有地标坐标，在这种情况下，纬度和经度将设置为零。这是地图转到0,0的另一个可能原因。

您似乎也在使用deprecated v2 Google geocoder。 This is the latest one但您可能希望转而使用CLGeocoder，除非您需要支持iOS4或更早版本。

显示kml数据？不，相反，地图将转到位置（0,0）

1 个答案: