@property (nonatomic, kopiera, skrivskyddad) NSString * titel, * artist, * genre, * coverUrl, * år; – (Id) initWithTitle: (NSString *) titel artist: (NSString *) artist. NFC Tools is an app which allows you to read, write and program tasks on your NFC tags and other RFID compatible chips. All you need to do is get your device . Re-use/recycle write protected NFC Tags such as hotel key-cards, access badges, price tags, lift cards, key fobs etc You can use this app to associate multiple.

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Denna variabel representerar skivomslaget bilden. Du har redan gjort kopieda bra skkrivskyddad hittills genom att skapa ett Album klass och en AlbumView klass. Eller ta en global konfiguration hanterare klass: I init du fylla arrayen med fem prov album. Hitta interface NSStringoch du kommer att se definitionen av klass tillsammans med tre kategorier: This defines a protocol named HorizontalScrollerDelegate that inherits from the NSObject protocol in the same way that an Objective-C class inherits from its parent.

iOS designmönster

It’s good practice to conform to the NSObject protocol — or to conform to a protocol that itself conforms to the NSObject protocol. You’ll soon see why this is important. You define the required and optional methods that the delegate will implement between the protocol and end lines. So add the following protocol methods:. Here you have both required and optional methods. Required methods must be implemented by the delegate and usually contain some data that is absolutely required by the class.

In this case, the required skriivskyddad are the number of views, the view at a specific index, and the behaviour when skrivsyddad view is tapped. The optional method here is the initial view; if it’s not implemented then the HorizontalScroller will default to the first index.

Next, you’ll need to refer to your new delegate from within the HorizontalScroller class definition. But the protocol definition is below the class definition and so is not visible at this point. The solution is to forward declare the protocol so that the compiler and Xcode knows that such a protocol will be available.

To do this, add the following code above the interface line:. The attribute of the property you created above is defined as weak. This is necessary in order to prevent a retain cycle.

Skribskyddad a class keeps a strong pointer to its skrivvskyddad and the delegate keeps a strong pointer back to the conforming class, your app will leak memory since neither class will release the memory allocated to the other. The id means that the delegate can only be assigned classes that conform to HorizontalScrollerDelegategiving you some type safety. The reload method is modelled after reloadData in UITableView ; it reloads all the data used to construct the horizontal scroller. The scroll view completely fills the HorizontalScroller.

Skrivakyddad UITapGestureRecognizer detects touches on the scroll view and checks if an album cover skrivskydfad been tapped. If so, it notifies the HorizontalScroller delegate. The gesture passed in xkrivskyddad a parameter lets you extract the location via locationInView: The HorizontalScroller instance has no information about the delegate other than knowing it can safely send this message since the delegate must conform to the HorizontalScrollerDelegate protocol.


For each view in the scroll view, perform a hit test using CGRectContainsPoint to find the view that was tapped. When the view is found, send the delegate the horizontalScroller: Before you break out of the for loop, center the tapped view in the scroll view. You execute reload when your data has changed. You also need to call this method when you add HorizontalScroller to another view.

Add the following code to HorizontalScroller. The didMoveToSuperview message is sent to a view when it’s added to another view as a subview. This is the right time to reload the contents of the scroller.

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The last piece of the HorizontalScroller puzzle is to make sure the album you’re viewing is always centered inside the scroll view. To do this, you’ll need to perform some calculations when the user drags the scroll view with their finger. The above code takes into account the current offset of the scroll view and the dimensions and the padding of the views in order to calculate the distance of the current view from the center. The last line is important: To detect that the user finished dragging inside the scroll view, you must add the following UIScrollViewDelegate methods:.

The decelerate parameter is true if the scroll view hasn’t come to a complete stop yet. When the scroll action ends, the the system calls scrollViewDidEndDecelerating. In both cases we should call the new method to center the current view since the current view probably has changed after the user dragged the scroll view.

Your HorizontalScroller is ready for use! Browse through the code you’ve just written; you’ll see there’s not one single mention of the Album or AlbumView classes. That’s excellent, because this means that the new scroller is truly independent and reusable. Now that HorizontalScroller is complete, it’s time to use it in your app. Now you can implement the delegate methods; you’ll be amazed at how just a few lines of code can implement a lot of functionality.

It’s common practice to place methods that fit together after a pragma mark directive. The compiler will ignore this line but if you drop down the list of methods in your current file via Xcode’s jump bar, you’ll see a separator and a bold title for the directive. This helps you organize your code for easy navigation in Xcode. This, as you’ll recognize, is the protocol method returning the number of views for the scroll view.

Since the scroll view will display covers for all the album data, the count is the number of album records. Here you create a new AlbumView and pass it to the HorizontalScroller.


Yes, you still need to actually create the scroller and add it to your main view kopirra before doing that, add the following method:. This method loads album data via LibraryAPI and then sets the currently displayed view based on the current value of the current view index. If the current view index is less than 0, meaning that no view was currently selected, then the first album in the list is displayed.

Otherwise, the last album is displayed. The above simply creates a new instance of HorizontalScrollersets its background color and delegate, adds the scroller to the main view, and then loads the subviews for the scroller to display album data.


If a protocol becomes too big and is packed with a lot of methods, you should consider breaking it into several smaller protocols. Try to design your protocols so that each one handles one specific area of functionality. Ah, that’s right — you didn’t implement the code to download the covers yet. To do that, you’ll need to add a way to download images. Since all your access to services goes through LibraryAPIthat’s where this new method would have to go.

However, there are a few things to consider first:. Sounds like a conundrum? Don’t despair, you’ll learn how to do this using the Observer pattern: In the Observer pattern, one object notifies other objects of any state changes. The objects involved don’t need to know about one another — thus encouraging a decoupled design. This pattern’s most often used to notify interested objects when a property has changed.

The usual implementation requires that an observer registers interest in iopiera state of another object. When the state changes, all the observing objects are notified of the change. Apple’s Push Notification service is a global example of this. If you want to stick to the MVC concept hint: And that’s where the Observer pattern comes in. Cocoa implements the observer pattern in two familiar ways: The publisher never needs to know anything about the subscribers.

Notifications are heavily used by Apple. This line sends a notification through the NSNotificationCenter kopiwra. That’s all the information you need to perform the cover download task.

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Add the following line to init in LibraryAPI. This is the other side of the equation: However, before you implement downloadImage: If you do not properly unsubscribe from a notification your class registered for, a notification might be sent to a deallocated instance.

This can result in application crashes. When this class is deallocated, it removes itself as an observer from all notifications it had registered for. There’s one more thing to do. It would probably be a good idea to save the downloaded covers locally so the app won’t need to download the same covers over and over again.

This code is pretty straightforward. The downloaded images will be saved in the Documents directory, and getImage: Again, you’re using the Facade pattern to hide the complexity of downloading an image from the other classes. The notification sender doesn’t care if the image came from the web or from the file system.

Build and run your app and check out the beautiful covers inside your HorizontalScroller:.

Stop your app and run it again. Notice that there’s no delay in loading the covers because they’ve been saved locally. You can even disconnect from the Internet and your app will work flawlessly. However, there’s one odd bit here: You started the spinner when downloading the image, but you haven’t implemented the logic to stop the spinner once the image is downloaded.

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