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Android 布局优化之<include/><merge/>和 <ViewStub>
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发布时间:2019-03-13

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By marking up a layout for reuse in Android development, developers often need to reuse complex components like title bars. This can be efficiently achieved by creating a reusable layout file called include_toolbar.xml, which contains a Toolbar widget with a TextView inside it.

Here’s an example of the include_toolbar.xml layout file:

Now, in your activity_main, you can include this toolbar layout using the <include> tag:

When using the <include> tag in your layout, here are some important points to keep in mind:

  • The <include> tag’s id attribute will override the id attribute of the included layout’s root node.
  • The <include> tag’s layout_* attributes will override the included layout’s root node’s layout_* attributes.
  • In ConstraintLayout, using the <include> tag requires the included view to have layout_width and layout_height attributes defined.
  • To reduce the layout hierarchy levels, you can use the <merge> tag when including views. This helps in avoiding unnecessary nested layouts, which can affect performance:

    When this view is included in another layout, the <merge> tag will be ignored, and the buttons will be placed directly in the布局.

    If you need to load a layout only when it’s actually required, you can use the <ViewStub> tag. This allows you to defer the loading of these layouts until they are needed:

    The ViewStub layout can be inflated when needed using either:

    val errorView = findViewById
    (R.id.view_stub).inflate()

    It’s important to note that inflate() can only be called once. After the first call, the ViewStub will no longer be part of the view hierarchy, and its original id will only be valid until the layout is inflated.

    By following these principles, you can efficiently manage layout reuse and optimize your Android development workflow.

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