This method updates the NSScroller objects to reflect the position and size of the visible portion of the document view. Its use outside of interaction with scroll views is discouraged, except in cases where the porting of an existing application is more straightforward. Configuring an NSScroller instance for use with a custom container view class or a completely different kind of target involves establishing a target-action relationship as defined by NSControl.
In the case of the scroll view, the target object is the content view. The target object is responsible for implementing the action method to respond to the scroller, and also for updating the scrollers in response to changes in target. As the scroller tracks the mouse, it sends an action message to its target object, passing itself as the parameter. The target object then determines the direction and scale of the appropriate scrolling action. It does this by sending the scroller a hitPart message. The hitPart method returns a part code that indicates where the user clicked in the scroller.
Table 1 shows the possible codes returned by the hitPart method. Table 1 Part codes returned by hitPart Scrolling behavior Part code returnedby hitPart The scroll view should not scroll at all. NSScrollerIncrementLine The scroll view should scroll up or to the left by the amount specified by the verticalLineScroll or horizontalLineScroll methods, dependent on the scroller's orientation. NSScrollerDecrementLine The scroll view should scroll down or to the right by the amount specified by the verticalPageScroll or horizontalPageScroll methods, dependent on the scroller's orientation.
NSScrollerIncrementPage The scroll view should scroll up or to the left by the amount specified by the verticalPageScroll or horizontalPageScroll methods, dependent on the scroller's orientation. NSScrollerDecrementPage The scroll view should scroll directly to the horizontal or vertical location—dependent on the scroller's orientation—returned by the scroller's floatValue method.
NSScrollerKnob or NSScrollerKnobSlot The target object tracks the size and position of its document view and updates the scroller to indicate the current position and visible proportion of the document view by sending the appropriate scrollers a setFloatValue: The knob proportion parameter is a floating-point value between 0 and 1 that specifies how large the knob in the scroller should appear. This article describes both procedures. Create the view, or views, that will be the document view of the scroll view.
Select that view, or views, that will be the scroll view's document view. This creates a new NSScrollView instance with the selected view, or views, as its document view. Open the inspector and configure the visible scrollers, background color, and line and page scroll amounts. Creating a Scroll View Programmatically Applications often create scroll views programmatically.
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After initializing the NSScrollView instance you must, at a minimum, set the document view using the method setDocumentView:. The example code in Listing 1 demonstrates how to create a scroll view for an NSImageView instance that is large enough to display the entire image. If they are not, redrawing in response to user scrolling is blurred. When created programmatically, scroll views have no scrollers. You specify that a scroll view should display scrollers by passing an argument of YES to the methods setHasVerticalScroller: The scroll view allocates and displays the scrollers automatically.
You can configure a scroll view to display its scrollers only when the document view is sufficiently large to require scrolling using the method setAutohidesScrollers: Calculating the Size of a Scroll View It is difficult to calculate the frame size of a scroll view if you know only the required size of the content view. The method returns a rectangle that is suitable for using with initWithFrame:.
Each of these values can be configured separately for a scroll view's horizontal and vertical scrolling directions. The line scroll increment moves the document view by a small amount, often in response to the user clicking the scroll buttons of a scroller. The line scroll increment is set for both horizontal and vertical directions using the setLineScroll: Alternatively, you can specify line scroll increment for the vertical and horizontal scrollers separately using the setVerticalLineScroll: The page scroll amount is specified using the setPageScroll: The page scroll amount differs from the line scroll increment in that the page scroll values specify the amount of visible view content that will remain when the document view scrolls.
Setting the page scroll value to 0.
Behind the Scenes of Collection Views
By default, a scroll viewupdates the contents dynamically as it scrolls. You disable dynamic scrolling by sending the setScrollsDynamically: In dynamic scrolling is turned off, updates occur only when the user releases the mouse. These cases are handled automatically by the NSScrollView class. Scrolling To a Specific Location Applications often need to scroll to a specific location in a document viewbecause of some user action unrelated to scrolling. For example, when a user searches a document they expect the document to scroll to show the found item.
The NSView class provides high-level scrolling methods that automatically update the scrollers and redisplay the document view as required. The NSClipView and NSScrollView classes methods provide low-level scrolling support that requires the application to update the scrollers and mark the document view for display. Two NSView methods support scrolling to reveal a specific location: These high-level methods scroll the specified point or rectangle to the origin of the content view.
You send these methods to the scroll view's document view or to one of its descendants. Scroll messages are passed up through the view hierarchy to the nearest enclosing NSClipView instance. NSView also provides a convenience method, enclosingScrollView, that returns the NSScrollView instance that contains the receiver, allowing the viewto interact directly with a parent scroll view.
If the receiver is not contained in a scroll view, enclosingScrollView returns nil. The code fragment in Listing 1 illustrates how to scroll to the top and bottom of the document view. The orientation of the document view determines where the origin of the content view lies and you must allow for this when calculating the top and bottom locations. Supporting autoscrolling allows the user to drag the mouse, moving or selecting items, and have the scroll view continually display the active portion of the document. View subclasses should send autoscroll: The autoscroll: Listing 2 shows a typical NSView subclass's implementation of a mouseDragged: Listing 2 Supporting automatic scrolling in a mouseDragged: The origin of the clip view's bounds is suitable for using with scrollPoint: The code fragment in Listing 3 demonstrates getting a scroll view's current scroll location and restoring it.
The adjustScroll: Listing 4 shows an implementation of adjustScroll: Listing 4 Constraining scrolling with adjustScroll: You synchronize the scrolling of two scroll view's by having the views register to receive notifications of the changes in the other's content view bounds. For example, an interface has two adjacent scroll views: The right scroll viewregisters to receive bounds notifications sent by the content view of the left scroll view. Similarly, the left scroll view registers for bounds notification changes sent by the right scroll view's content view. When a scroll viewreceives a bounds change notification, it determines which content view changed by examining the object returned by sending the notification an object method.
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It then checks to see if its origin is already at the origin of the content view bounds and if it is not, it scrolls to that location. This check ensures that the scroll view doesn't scroll if it is already at the correct location, preventing notifications being sent to the other scroll view and causing an infinite loop.
Implementing this synchronizing in a generic way is best done by subclassing NSScrollView.
The SynchroScrollView class example synchronizes scrolling only in the vertical plane and requires the following: The SynchroScrollView implementation relies on the scroll view being retained by some other object, typically the view hierarchy itself. It is the application's responsibility to break the synchronization between the views before the views are deallocated. Listing 1 shows the class declaration.
Listing 1 SynchroScrollView. Both scroll views that are synchronized are set as each other's synchronizedScrollView. You still need to instantiate it. Put it into action now — open ViewController. A collection view without data is like a magic act with no slight of hand — pointless and uninspiring. Open the Connections Inspector and locate dataSource in the Outlets section. Build and run. It was worth all that work! Your collection view displays images from the Desktop Pictures folder!
You worked through several steps, so you probably just missed something small. First, you need to add a check box at the bottom of the view so you can toggle between single and multi-section. Open the Size Inspector and change its Constant to Now for a little UI. The number of elements in this array sets the max number of sections, and the element values set the number of items in each section.
Now, open Main. In the black pop-up window click showHideSections: You can check if the connection was set properly in the Connections Inspector.
A Beginner’s Guide to UIScrollView
To fix this, open ViewController. Here you set the bottom and top section insets to 30 to provide better visual separation between sections. Another way to see section boundaries is adding a header or footer view. To do this, you need a custom NSView class and will need to implement a data source method to provide the header views to the table view. Open HeaderView. Open the Size Inspector and change Width to and Height to Drag a label from the Object Library to the left-hand side of Custom View.
With the interface ready for show time, the next task is to create a custom view subclass for the header view. Click next, and for Group select Views. Click Create. With the framework in place, the next task is changing the nib file to use this new class and connecting the outlets to the labels.
Open the Identity Inspector.
Change the Class to HeaderView. In the black pop-up window, drag from imageCount to the Images Count label on the canvas to connect the outlet. Repeat the operation for the second label, dragging from sectionTitle to the Section Number label in the canvas.
The collection view calls this method when it needs the data source to provide a header for a section. The method:. At the end of ViewController. The above method, although technically optional, is a must when you use headers because the flow layout delegate needs to provide the size of the header for every section.
In this case, the method returns a size of zero when the collection view is in single section mode, and it returns 40 when in multiple sections mode. Open the Connections Inspector , and locate the delegate in the Outlets section. Drag from the button next to it to the view controller in the Document Outline. Collection views support both single and multiple selections. To show an item as selected, you must highlight it.
Before you can do that, you need to make the collection view selectable. Open the Main.
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Checking Selectable enables single selection, meaning you can click an item to select it. And when you choose a different item, it deselects the previous item and selects item you just picked. Non-selected items will get no special treatment. Open CollectionViewItem. Add the following at the end of viewDidLoad:. When the user selects an item in the collection view, you find out via delegate methods.