在内存中保持mkmapsnapshot为NSData

Question

我正试图截取我的MKMapView的屏幕截图。我通常使用Objective c中的以下代码来实现这一点。

我想知道我如何保持NSData对象在内存中，而不是保存图像，然后从它直接读取。

我也想知道如何在Swift中编写-特别是完成处理程序部分。我看了文档-但不确定语法:https://developer.apple.com/library/prerelease/iOS/documentation/MapKit/Reference/MKMapSnapshotter_class/index.html#//apple_ref/c/tdef/MKMapSnapshotCompletionHandler

MKMapSnapshotOptions *options = [[MKMapSnapshotOptions alloc] init];
options.region = self.mapView.region;
options.size = self.mapView.frame.size;
options.scale = [[UIScreen mainScreen] scale];
NSURL *fileURL = [NSURL fileURLWithPath:@"path/to/snapshot.png"];
MKMapSnapshotter *snapshotter = [[MKMapSnapshotter alloc] initWithOptions:options];
[snapshotter startWithCompletionHandler:^(MKMapSnapshot *snapshot, NSError *error) {
    if (error) {
        NSLog(@"[Error] %@", error);
        return;
    }
    UIImage *image = snapshot.image;
    NSData *data = UIImagePNGRepresentation(image);
    [data writeToURL:fileURL atomically:YES];
}];

Answer 1

在"保持"它在内存中，你可以通过一个Objective-C完成块(或Swift闭包)返回NSData。从那里，您可以将NSData传递给另一个方法或将其保存在类属性中。

例如，在Objective-C中:

/** Request NSData of PNG representation of map snapshot.
 *
 * @param mapView The MKMapView for which we're capturing the snapshot
 * @param completion The completion block that will be called when the asynchronous snapshot is done. This takes two parameters, the resulting NSData upon success and an NSError if there was an error.
 */
- (void)requestSnapshotDataForMapView:(MKMapView *)mapView completion:(void (^)(NSData *data, NSError *error))completion
{
    MKMapSnapshotOptions *options = [[MKMapSnapshotOptions alloc] init];
    options.region = mapView.region;
    options.size = mapView.frame.size;
    options.scale = [[UIScreen mainScreen] scale];
    MKMapSnapshotter *snapshotter = [[MKMapSnapshotter alloc] initWithOptions:options];
    [snapshotter startWithCompletionHandler:^(MKMapSnapshot *snapshot, NSError *error) {
        if (error) {
            if (completion) {
                completion(nil, error);
            }
            return;
        }
        UIImage *image = snapshot.image;
        NSData *data = UIImagePNGRepresentation(image);
        if (completion) {
            completion(data, nil);
        }
    }];
}
- (IBAction)didTouchUpInsideButton:(id)sender
{
    [self requestSnapshotDataForMapView:self.mapView completion:^(NSData *data, NSError *error) {
        if (error) {
            NSLog(@"requestSnapshotDataForMapView error: %@", error);
            return;
        }
        // do whatever you want with the `data` parameter here, for example,
        // if you had some `@property (nonatomic, strong) NSData *snapshotData;`,
        // you might do:
        //
        // self.snapshotData = data
        // now initiate the next step of the process in which you're presumably
        // going to use the `data` provided by this block.
    }];
}

在Swift中对应的是:

/// Request NSData of PNG representation of map snapshot.
///
/// - parameter mapView:     The MKMapView for which we're capturing the snapshot
/// - parameter completion:  The closure that will be called when the asynchronous snapshot is done. This takes two parameters, the resulting NSData upon success and an NSError if there was an error.
func requestSnapshotData(mapView: MKMapView, completion: (NSData?, NSError?) -> ()) {
    let options = MKMapSnapshotOptions()
    options.region = mapView.region
    options.size = mapView.frame.size
    options.scale = UIScreen.mainScreen().scale
    let snapshotter = MKMapSnapshotter(options: options)
    snapshotter.startWithCompletionHandler() { snapshot, error in
        guard snapshot != nil else {
            completion(nil, error)
            return
        }
        let image = snapshot!.image
        let data = UIImagePNGRepresentation(image)
        completion(data, nil)
    }
}
@IBAction func didTouchUpInsideButton(sender: AnyObject) {
    requestSnapshotData(mapView) { data, error in
        guard data != nil else  {
            print("requestSnapshotData error: (error)")
            return
        }
        // do whatever you want with the `data` parameter here, for example,
        // if you had some `var snapshotData: NSData?` class property, you might do:
        //
        // self.snapshotData = data
        // now initiate the next step of the process in which you're presumably
        // going to use the `data` provided by this closure.
    }
}

坦率地说，如果您试图在其他地方使用UIImage，我可能会更改这些块/闭包参数以使用UIImage而不是NSData，但希望这说明了这个想法。