为什么滚动是通过处理程序处理的，而调整大小是通过 ScrollPanel 中的重写方法处理的？
为什么GWT要这样设计呢？调整大小和滚动事件之间的主要区别是什么？
Why is GWT designed in such a way? What is the principal difference between resize and scroll events?
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因为浏览器中没有用于调整大小的事件（在窗口级别调整大小，但不是元素级别），这与滚动事件相反。
因此，调整“通知”大小在 GWT 中是“模拟”的：如果您使用
RootLayoutPanel或ResizeLayoutPanel，它将侦听窗口调整大小事件并将它们向下传播到其 < code>RequiresResize 子级（如果它们本身是ProvidesResize小部件，它们也会向下传播）。显式设置
ProvidesResize小部件的大小也会通知其RequiresResize子部件；以及调整布局面板区域的大小（以编程方式用于DockLayoutPanel和LayoutPanel以及其他），和/或由用户为SplitLayoutPanel完成> 或 StackLayoutPanel）。您会注意到，
ScrollPanel既是RequiresResize（将由其父ProvidesResize小部件通知其大小可能已更改），又是>ProvidesResize（如果它是RequiresResize，将通知其子小部件）。Because there's no event for resizing in browsers (there's resizing at the window-level, but not element-level), contrary to scroll events.
Thus, resizing "notification" is "emulated" in GWT: if you use a
RootLayoutPanelorResizeLayoutPanel, it'll listen for window resize events and propagates them downwards to itsRequiresResizechildren (which will propagate downwards too, if they areProvidesResizewidgets themselves).Explicitly setting the size of a
ProvidesResizewidget will also notify itsRequiresResizechildren; as well as resizing areas of a layout panel (programmatically forDockLayoutPanelandLayoutPanel–among others–, and/or done by the user for aSplitLayoutPanelorStackLayoutPanel).You'll note that
ScrollPanelis both aRequiresResize(will be notified by its parentProvidesResizewidget that its size might have changed) andProvidesResize(will notify its child widget if its aRequiresResize).