View roots

A view root manages and maintains the connection between a view hierarchy and the device on which the hierarchy is displayed. A view root is associated with a display device and can adopt a single view.

When a view root adopts a view, it becomes the owner of the view and any view hierarchy under it. The adopted view hierarchy appears on the display device associated with the view root. (This is a simplified explanation. Actually, the adopted view is initially marked "invalid" and the View System eventually requests that it refresh itself. See "Drawing by invalidation" on page 83 for details.)

When the view root orphans the view (or when the view root itself is deleted), the view and any hierarchy under it disappear from the display device. Figure 20 and Figure 21 illustrate the relationship between a view hierarchy, a view root, and a display device.




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