You can use a [UILongPressGestureRecognizer][1] for this.  Wherever you create or initialize the mapview, first attach the recognizer to it:

    UILongPressGestureRecognizer *lpgr = [[UILongPressGestureRecognizer alloc] 
        initWithTarget:self action:@selector(handleLongPress:)];
    lpgr.minimumPressDuration = 2.0; //user needs to press for 2 seconds
    [self.mapView addGestureRecognizer:lpgr];
    [lpgr release];

Then in the gesture handler:

    - (void)handleLongPress:(UIGestureRecognizer *)gestureRecognizer
    {
    	if (gestureRecognizer.state != UIGestureRecognizerStateBegan)
    		return;
    	
    	CGPoint touchPoint = [gestureRecognizer locationInView:self.mapView];	
    	CLLocationCoordinate2D touchMapCoordinate = 
            [self.mapView convertPoint:touchPoint toCoordinateFromView:self.mapView];
    	
    	YourMKAnnotationClass *annot = [[YourMKAnnotationClass alloc] init];
    	annot.coordinate = touchMapCoordinate;
    	[self.mapView addAnnotation:annot];
    	[annot release];
    }

YourMKAnnotationClass is a class you define that conforms to the [MKAnnotation][2] protocol.  If your app will only be running on iOS 4.0 or later, you can use the pre-defined [MKPointAnnotation][3] class instead.

For examples on creating your own MKAnnotation class, see the sample app [MapCallouts][4].


  [1]: https://developer.apple.com/documentation/uikit/uilongpressgesturerecognizer
  [2]: https://developer.apple.com/documentation/mapkit/mkannotation
  [3]: https://developer.apple.com/documentation/mapkit/mkpointannotation
  [4]: https://developer.apple.com/documentation/mapkit/mapkit_annotations/annotating_a_map_with_custom_data

Thanks to Anna for providing such a great answer! Here is a Swift version if anybody is interested (the answer has been updated to Swift 4.1 syntax).

Creating UILongPressGestureRecognizer: 

    let longPressRecogniser = UILongPressGestureRecognizer(target: self, action: #selector(MapViewController.handleLongPress(_:)))
    longPressRecogniser.minimumPressDuration = 1.0
    mapView.addGestureRecognizer(longPressRecogniser)

Handling the gesture:

    @objc func handleLongPress(_ gestureRecognizer : UIGestureRecognizer){
        if gestureRecognizer.state != .began { return }
        
        let touchPoint = gestureRecognizer.location(in: mapView)
        let touchMapCoordinate = mapView.convert(touchPoint, toCoordinateFrom: mapView)
        
        let album = Album(coordinate: touchMapCoordinate, context: sharedContext)

        mapView.addAnnotation(album)
    }

I would like set up a polymorphic relation with `accepts_nested_attributes_for`. Here is the code:

    class Contact &lt;ActiveRecord::Base
      has_many :jobs, :as=&gt;:client
    end
    
    class Job &lt;ActiveRecord::Base
      belongs_to :client, :polymorphic=&gt;:true
      accepts_nested_attributes_for :client
    end

When I try to access `Job.create(..., :client_attributes=&gt;{...}` gives me `NameError: uninitialized constant Job::Client`

accepts_nested_attributes_for with belongs_to polymorphic

I want to check if my array is empty or null, and on base of which I want to create a condition for example.

    if(array ==  EMPTY){
    //do something
    }

I hope I&#39;m clear what I am asking, just need to check if my array is empty?

regards

How to check if array is null or empty?

I had to get the coordinate of a point where the user touch on a MKMapView.
I&#39;m not working with the Interface Builder.
Can you give me one example?


How to add a push pin to a MKMapView(IOS) when touching?

<p>I had to get the coordinate of a point where the user touch on a MKMapView.
I'm not working with the Interface Builder.
Can you give me one example?</p>


I am working on a project on which I have to preselect a particular cell.

I can preselect a cell using `-willDisplayCell`, but I can&#39;t deselect it when the user clicks on any other cell.  

    - (void)tableView:(UITableView*)tableView 
            willDisplayCell:(UITableViewCell*)cell
            forRowAtIndexPath:(NSIndexPath*)indexPath
    { 
        AppDelegate_iPad *appDelegte = 
          (AppDelegate_iPad *)[[UIApplication sharedApplication] delegate];
  
        if ([appDelegte.indexPathDelegate row] == [indexPath row])
        {
            [cell setSelected:YES];    
        } 
    }

    - (void)tableView:(UITableView *)tableView 
            didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
    
        AppDelegate_iPad *appDelegte = 
          (AppDelegate_iPad *)[[UIApplication sharedApplication] delegate];
  
        NSIndexPath *indexpath1 = appDelegte.indexPathDelegate;
        appDelegte.indexPathDelegate = indexPath;
        [materialTable deselectRowAtIndexPath:indexpath1 animated:NO];
    }

Can you help?

How to deselect a selected UITableView cell?

In Javascript/jQuery, how can I detect if the client device has a mouse?  

I&#39;ve got a site that slides up a little info panel when the user hovers their mouse over an item.  I&#39;m using jQuery.hoverIntent to detect the hover, but this obviously doesn&#39;t work on touchscreen devices like iPhone/iPad/Android. So on those devices I&#39;d like to revert to tap to show the info panel.



Detecting touch screen devices with Javascript

I am using addTarget:action:forControlEvents like this:

&lt;pre&gt;&lt;code&gt;[newsButton addTarget:self
action:@selector(switchToNewsDetails)
forControlEvents:UIControlEventTouchUpInside];
&lt;/pre&gt;&lt;/code&gt;

and I would like to pass parameters to my selector &quot;switchToNewsDetails&quot;.
The only thing I succeed in doing is to pass the (id)sender by writing:
&lt;pre&gt;&lt;code&gt;action:@selector(switchToNewsDetails:)&lt;/pre&gt;&lt;/code&gt;

But I am trying to pass variables like integer values. Writing it this way doesn&#39;t work :

&lt;pre&gt;&lt;code&gt;int i = 0;
[newsButton addTarget:self
action:@selector(switchToNewsDetails:i)
forControlEvents:UIControlEventTouchUpInside];
&lt;/pre&gt;&lt;/code&gt;

Writing it this way does not work either:

&lt;pre&gt;&lt;code&gt;int i = 0;
[newsButton addTarget:self
action:@selector(switchToNewsDetails:i:)
forControlEvents:UIControlEventTouchUpInside];
&lt;/pre&gt;&lt;/code&gt;

Any help would be appreciated :)

Passing parameters to addTarget:action:forControlEvents

I have a URL like `myApp://action/1?parameter=2&amp;secondparameter=3`

With the property query I get following part of my `URL`

    parameter=2&amp;secondparameter=3

Is there any way easy to put this in a `NSDictionary` or an `Array`?

Thx a lot


Parse NSURL query property

My project has a `UIImage` category function that I want to call from another class. I properly import the header file for the image category and I get the project to compile with no warning.

The problem is that when I call the `UIImage` category function I seen an unrecognized selector error with a `NSInvalidArgumentException`. Why am I seeing this if I&#39;ve properly linked everything?

    #import &lt;UIKit/UIKit.h&gt;
    
    @interface UIImage (DRShare)
    
    + (UIImage*) imageNamed:(NSString*)name;
    
    @end
   

    @implementation UIImage (DRShare)
    
    + (UIImage*) imageNamedDR:(NSString*)name{
    	
    	CGFloat s = 1.0f;
    	if([[UIScreen mainScreen] respondsToSelector:@selector(scale)]){
    		s = [[UIScreen mainScreen] scale];
    	}
    	
    	NSString *path = [NSString stringWithFormat:@&quot;%@%@%@.png&quot;,kImagesPath,name,s &gt; 1 ? @&quot;@2x&quot;:@&quot;&quot;];
    	return [UIImage imageWithContentsOfFile:DRBUNDLE(path)];
    }
    
    @end

file that calls it:
   
    		backgroundView = [[UIImageView alloc] initWithImage:[UIImage imageNamedDR:@&quot;Share Popup Background&quot;]];

exception raised:

    2010-10-22 11:51:02.880 Stuff[11432:207] +[UIImage imageNamedDR:]: unrecognized selector sent to class 0x1f8e938
    2010-10-22 11:51:02.883 Stuff[11432:207] *** Terminating app due to uncaught exception &#39;NSInvalidArgumentException&#39;, reason: &#39;+[UIImage imageNamedDR:]: unrecognized selector sent to class 0x1f8e938&#39;
    *** Call stack at first throw:
    (
    	0   CoreFoundation                      0x02e65b99 __exceptionPreprocess + 185
    	1   libobjc.A.dylib                     0x02fb540e objc_exception_throw + 47
    	2   CoreFoundation                      0x02e6776b +[NSObject(NSObject) doesNotRecognizeSelector:] + 187
    	3   CoreFoundation                      0x02dd72b6 ___forwarding___ + 966
    	4   CoreFoundation                      0x02dd6e72 _CF_forwarding_prep_0 + 50
    	5   TapTapShare                         0x0001291c -[DRShareViewController backgroundView] + 127
    	6   TapTapShare                         0x00012343 -[DRShareViewController loadView] + 639
    	7   UIKit                               0x0044f54f -[UIViewController view] + 56
    	8   UIKit                               0x0044d9f4 -[UIViewController contentScrollView] + 42
    	9   UIKit                               0x0045d7e2 -[UINavigationController _computeAndApplyScrollContentInsetDeltaForViewController:] + 48
    	10  UIKit                               0x0045bea3 -[UINavigationController _layoutViewController:] + 43
    	11  UIKit                               0x0045d12d -[UINavigationController _startTransition:fromViewController:toViewController:] + 524
    	12  UIKit                               0x00457ccd -[UINavigationController _startDeferredTransitionIfNeeded] + 266
    	13  UIKit                               0x00574b55 -[UILayoutContainerView layoutSubviews] + 226
    	14  QuartzCore                          0x02616481 -[CALayer layoutSublayers] + 177
    	15  QuartzCore                          0x026161b1 CALayerLayoutIfNeeded + 220
    	16  QuartzCore                          0x026160bd -[CALayer layoutIfNeeded] + 111

Objective-C Category Causing unrecognized selector


I have a view that has rows and columns of imageviews in it.

If this view is resized, I need to rearrange the imageviews positions.

This view is a subview of another view that gets resized.

Is there a way to detect when this view is being resized?



Is there a UIView resize event?

I often want to execute some code a few microseconds in the future. Right now, I solve it like this:

    - (void)someMethod
    {
        // some code
    }

And this:

    [self performSelector:@selector(someMethod) withObject:nil afterDelay:0.1];

It works, but I have to create a new method every time. Is it possible to use blocks instead of this? Basically I&#39;m looking for a method like:

    [self performBlock:^{
        // some code
    } afterDelay:0.1];

That would be really useful to me.

Blocks instead of performSelector:withObject:afterDelay:

I want to debug my PhoneGap app in Xcode, but its Console can not show javascript errors.

How to see the javascript errors of PhoneGap app in Xcode?

I am using MKMapView and have added a number of annotation pins to the map about a 5-10 kilometre area. When I run the application my map starts zoomed out to show the whole world, what is the best way to zoom the map so the pins fit the view?

**EDIT:**
My initial thinking would be to use MKCoordinateRegionMake and calculate the coordinate centre, longitudeDelta and latitudeDelta from my annotations. I am pretty sure this will work, but I just wanted to check I was not missing anything obvious.

Code added, BTW: FGLocation is an class that conforms to `MKAnnotation`, locationFake is an `NSMutableArray` of these objects. Comments are always welcome ....

    - (MKCoordinateRegion)regionFromLocations {
        CLLocationCoordinate2D upper = [[locationFake objectAtIndex:0] coordinate];
        CLLocationCoordinate2D lower = [[locationFake objectAtIndex:0] coordinate];
        
        // FIND LIMITS
        for(FGLocation *eachLocation in locationFake) {
            if([eachLocation coordinate].latitude &gt; upper.latitude) upper.latitude = [eachLocation coordinate].latitude;
            if([eachLocation coordinate].latitude &lt; lower.latitude) lower.latitude = [eachLocation coordinate].latitude;
            if([eachLocation coordinate].longitude &gt; upper.longitude) upper.longitude = [eachLocation coordinate].longitude;
            if([eachLocation coordinate].longitude &lt; lower.longitude) lower.longitude = [eachLocation coordinate].longitude;
        }
        
        // FIND REGION
        MKCoordinateSpan locationSpan;
        locationSpan.latitudeDelta = upper.latitude - lower.latitude;
        locationSpan.longitudeDelta = upper.longitude - lower.longitude;
        CLLocationCoordinate2D locationCenter;
        locationCenter.latitude = (upper.latitude + lower.latitude) / 2;
        locationCenter.longitude = (upper.longitude + lower.longitude) / 2;
    
        MKCoordinateRegion region = MKCoordinateRegionMake(locationCenter, locationSpan);
        return region;
    }




Zooming MKMapView to fit annotation pins?

Is there a way to determine if a MKMapView was dragged around?

I want to get the center location every time a user drags the map using `CLLocationCoordinate2D centre = [locationMap centerCoordinate];` but I&#39;d need a delegate method or something that fires as soon as the user navigates around with the map.

Thanks in advance

determine if MKMapView was dragged/moved

I have two UITextFields which users can enter in a latitude and longitude, these co-ordinates are then used to create a pin on an MKMapView.

I want find a way to validate whether the values they enter are actual GPS co-ordinates or just a load of rubbish. Is there any way of doing this?

How to validate latitude and longitude

I&#39;m trying to update an MKMapView by removing all annotations outside the visible area, and adding and removing some annotations inside the visible area. This is my code:

    NSSet *visibleAnnotations = [mapView annotationsInMapRect:[mapView visibleMapRect]];
    NSSet *allAnnotations = [NSSet setWithArray:[mapView annotations]];
    NSMutableSet *nonVisibleAnnotations = [NSMutableSet setWithSet:allAnnotations];
    [nonVisibleAnnotations minusSet:visibleAnnotations];
    [mapView removeAnnotations:(NSArray *)nonVisibleAnnotations];
    
    NSMutableSet *newAnnotations = [NSMutableSet setWithArray:[_zoomLevels objectAtIndex:clusterLevel]];
    [newAnnotations minusSet:visibleAnnotations];
    [mapView addAnnotations:(NSArray *)newAnnotations];

This gives me the error **-[__NSCFSet objectAtIndex:]: unrecognized selector sent to instance 0x13cd40** after the final line in which I cast newAnnotations to an NSArray then add the annotations. Is there something about casting an array to a set that causes this? If so, is there a way round it?

NSSet to NSArray casting calling objectAtIndex?

*(Using iOS 5 and Xcode 4.2)*

I have an MKMapView and want to draw a circle of 1000m radius around the user location.

On the surface it would seem that implementing the [mapView:viewForAnnotation:][1]  map view delegate method, and adding a custom MKAnnotationView for the users location, would be a perfect solution. It would look something like this:

    - (MKAnnotationView *)mapView:(MKMapView *)mapView
                viewForAnnotation:(id &lt;MKAnnotation&gt;)annotation
    {
        // If it&#39;s the user location, return my custom MKAnnotationView.
        if ([annotation isKindOfClass:[MKUserLocation class]]) {
            return myCustomAnnotationView;
        } else {
            return nil;
        }
    }

However annotations on the map don&#39;t scale when you zoom in and out of the map. 

So I tried adding an overlay (because overlays scale with the map), using the [MKCircle][2] class and setting its co-ordinates to the latest co-ordinates from my locationManger/map view delegate. However as the [coordinate property][3] of MKCircle is readonly, I&#39;m having to remove the overlay then add a new one each time the user moves. Causing a noticeable flicker as it happens.

Is there any way to make an annotation scale seamlessly as the map view is scaled in and out? Or is there a good way to make an overlay move seamlessly with changes in the users location?

I would be very grateful for your help :)


  [1]: http://developer.apple.com/library/ios/#documentation/MapKit/Reference/MKMapViewDelegate_Protocol/MKMapViewDelegate/MKMapViewDelegate.html#//apple_ref/doc/uid/TP40008204
  [2]: http://developer.apple.com/library/IOs/#documentation/MapKit/Reference/MKCircle_class/Reference/Reference.html
  [3]: http://developer.apple.com/library/IOs/#documentation/MapKit/Reference/MKCircle_class/Reference/Reference.html

Content Type	Original Author	Original Content on Stackoverflow
Question	Christophe Debove	View Question on Stackoverflow
Solution 1 - Iphone	user467105	View Answer on Stackoverflow
Solution 2 - Iphone	Allan Spreys	View Answer on Stackoverflow

How to add a push pin to a MKMapView(IOS) when touching?

Iphone Problem Overview

Iphone Solutions

Solution 1 - Iphone

Solution 2 - Iphone

How to check if array is null or empty?

accepts_nested_attributes_for with belongs_to polymorphic

Attributions