呈现网格会引起子部件创建并加入页面，如清单4所示。

Rendering the grid causes all its child widgets to be created and added to the page, as shown below in Listing 4.

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在这个示例中使用的VBox部件是一种布局部件，它垂直地排列子部件。

The VBox widget used in this example is a type of layout widget that stacks its children vertically.

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下一步，我们将在这个主窗口中创建标签和按钮对象，作为主窗口的子部件。

Next, we've created Label and Button objects as child widgets inside the MainWindow.

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