{"id":20154,"date":"2013-05-10T11:47:56","date_gmt":"2013-05-10T06:17:56","guid":{"rendered":"http:\/\/vskills.in\/certification\/tutorial\/?p=20154"},"modified":"2024-04-12T14:16:05","modified_gmt":"2024-04-12T08:46:05","slug":"view-hierarchy-and-switching","status":"publish","type":"page","link":"https:\/\/www.vskills.in\/certification\/tutorial\/view-hierarchy-and-switching\/","title":{"rendered":"View Hierarchy and switching"},"content":{"rendered":"

View Hierarchy and switching<\/strong><\/h4>\n

What Is a View Hierarchy?<\/h2>\n

In addition to being responsible for drawing and handling user events, a view instance can act as a container, enclosing other view instances. Those views are linked together creating a\u00a0view hierarchy<\/strong>. Unlike a class hierarchy, which defines the lineage of a class, the view hierarchy defines the layout of views relative to other views.<\/p>\n

The window instance maintains a reference to a single top-level view instance, call the\u00a0content view. The content view acts as the root of the visible view hierarchy in a window. The view instances enclosed within a view are called\u00a0subviews.<\/strong> The parent view that encloses a view is referred to as its\u00a0superview<\/strong>. While a view instance can have multiple subviews, it can have only one superview. In order for a view and its subviews to be visible to the user, the view must be inserted into a window’s view hierarchy.<\/p>\n

\"view_hierarchy_enclose_1\"<\/a><\/p>\n

This window’s view hierarchy has these parts.<\/p>\n

    \n
  1. The window is represented by an NSWindow instance.<\/span><\/li>\n
  2. The content view serves as the root of the window’s view hierarchy.<\/span><\/li>\n
  3. The content view contains a single subview, an instance of a custom class (that looks remarkably like an NSBox, but is not.).<\/span><\/li>\n
  4. The custom view instance that, in turn has two subviews, an NSButton instance, and an NSTextField instance.<\/span><\/li>\n
  5. The superview for both the button and text field is the NSBox object. The custom view container actually encloses the button and text field views.<\/span><\/li>\n<\/ol>\n

    Locating Views in the View Hierarchy<\/h2>\n

    A rich selection of methods allows applications to access a view’s hierarchy. The\u00a0superview<\/code>\u00a0method returns the view that contains the receiver, while the\u00a0subviews<\/code>\u00a0method returns an array containing the view’s immediate descendants. If a view is the root of a view hierarchy, it returns\u00a0nil<\/code>\u00a0when asked for its superview. Sending a view the\u00a0window<\/code>\u00a0message returns the window the view resides in, or\u00a0nil<\/code>\u00a0if the view is not currently in a window’s view hierarchy.<\/p>\n

    \"contents_sub_super_views_2x<\/a><\/p>\n

    Other methods allow you to inspect relationships among views:\u00a0isDescendantOf:<\/code>\u00a0confirms the containment of the receiver;\u00a0ancestorSharedWithView:<\/code>\u00a0finds the common container containing the receiver and the view instance specified as the parameter. For example, assuming a view hierarchy as shown in\u00a0Figure 3-2, sendingviewC<\/code>\u00a0a\u00a0isDescendentOf:<\/code>\u00a0message with\u00a0contentView<\/code>\u00a0as the parameter returns\u00a0YES<\/code>. Sending\u00a0viewB<\/code>\u00a0theancestorSharedWithView:<\/code>\u00a0message, passing\u00a0viewC<\/code>\u00a0as the parameter, returns\u00a0viewA<\/code>.<\/p>\n

    The\u00a0opaqueAncestor<\/code>\u00a0method returns the closest parent view that\u2019s guaranteed to draw every pixel in the receiver\u2019s frame (possibly the receiver itself).<\/p>\n

    \n

    Apply for iPhone Apps Certification Now!!<\/h3>\n

    http:\/\/www.vskills.in\/certification\/Certified-iPhone-Apps-Developer<\/a><\/p>\n

    Back to Tutorial<\/strong><\/a><\/h4>\n<\/div>\n","protected":false},"excerpt":{"rendered":"

    View Hierarchy and switching What Is a View Hierarchy? In addition to being responsible for drawing and handling user events, a view instance can act as a container, enclosing other view instances. Those views are linked together creating a\u00a0view hierarchy. Unlike a class hierarchy, which defines the lineage of a class, the view hierarchy defines…<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"categories":[3347],"tags":[4507,4506],"class_list":["post-20154","page","type-page","status-publish","hentry","category-iphone-apps","tag-view-hierarchy","tag-view-hierarchy-and-switching"],"acf":[],"yoast_head":"\nView Hierarchy and switching - Tutorial<\/title>\n<meta name=\"description\" content=\"View Hierarchy and switching\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.vskills.in\/certification\/tutorial\/view-hierarchy-and-switching\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"View Hierarchy and switching - 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