Android Support4Demos的FragmentTabs示例中的两个框架布局

Question

我对Android中的片段是新手，我指的是为supprotv4兼容性库提供的片段演示示例。

谁能解释一下为什么在Android Support4Demos的FragmentTabs.java例子中有两个框架布局(@+android:id/realtabcontent , @android:id/tabcontent)。

FragmentTabs.java调用setContentView(R.layout.fragment_tabs);方法，下面是该方法的布局文件。

fragment_tabs.xml

    <TabHost xmlns:android="http://schemas.android.com/apk/res/android"
        android:id="@android:id/tabhost"
        android:layout_width="match_parent"
        android:layout_height="match_parent" >

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:orientation="vertical" >

            <TabWidget
                android:id="@android:id/tabs"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_weight="0"
                android:orientation="horizontal" />

            <FrameLayout
                android:id="@android:id/tabcontent"
                android:layout_width="0dp"
                android:layout_height="0dp"
                android:layout_weight="0" />

            <FrameLayout
                android:id="@+android:id/realtabcontent"
                android:layout_width="match_parent"
                android:layout_height="0dp"
                android:layout_weight="1" />
        </LinearLayout>

    </TabHost>

提前感谢

Answer 1

浏览完示例后，我在FragmentsTabs.java中找到了以下注释

 /**
 * This is a helper class that implements a generic mechanism for
 * associating fragments with the tabs in a tab host. It relies on a trick.
 * Normally a tab host has a simple API for supplying a View or Intent that
 * each tab will show. This is not sufficient for switching between
 * fragments. So instead we make the content part of the tab host 0dp high
 * (it is not shown) and the TabManager supplies its own dummy view to show
 * as the tab content. It listens to changes in tabs, and takes care of
 * switch to the correct fragment shown in a separate content area whenever
 * the selected tab changes.
 */