Android架构组件-Navigation的使用(一)

在 Google I/O 2018 上新出现了一个导航组件（Navigation Architecture Component），导航组件类似iOS开发里的StoryBoard，可以可视化的编辑App页面的导航关系。
官方文档：The Navigation Architecture Component
官方教程：Navigation Codelab
学习Demo：navigation
Google实验室的Demo: android-navigation

 

导航（Navigation）规则

1. App需要有确定的起始点
2. 使用一个栈来代表App的导航状态
3. 向上按钮从不会退出你的App
4. 在App任务中向上和返回按钮是等价的
5. 深度链接到目标或导航到相同的目标应产生相同的堆栈

Navigation的使用

Navigation 是 Android Studio 3.2 才有的功能，所以要先下载 Android Studio 3.2, 目前 Android Studio 3.2 是预览版，正式版目前是 3.1.3，Android studio3.2/3.3下载页面

 

Android studio

下载完 Android Studio 3.2 /3.3 后打开项目

在 app 下的 build.gradle 导入 Navigation：

 

dependencies {
    //...
    implementation "android.arch.navigation:navigation-fragment-ktx:1.0.0-alpha04"
    implementation "android.arch.navigation:navigation-ui-ktx:1.0.0-alpha04"
}

建立个Activity，需要用到 NavHost 来托管 Navigation，NavHost 是个接口，默认是用 NavHostFragment 来托管，NavHostFragment 是实现了 NavHost 接口的，查看 NavHostFragment 会看到，在注释里他已经提供了简单的activity布局写法

 

/**
 * NavHostFragment provides an area within your layout for self-contained navigation to occur.
 *
 * <p>NavHostFragment is intended to be used as the content area within a layout resource
 * defining your app's chrome around it, e.g.:</p>
 *
 * <pre class="prettyprint">
 * &lt;android.support.v4.widget.DrawerLayout
 *        xmlns:android="http://schemas.android.com/apk/res/android"
 *        xmlns:app="http://schemas.android.com/apk/res-auto"
 *        android:layout_width="match_parent"
 *        android:layout_height="match_parent"&gt;
 *    &lt;fragment
 *            android:layout_width="match_parent"
 *            android:layout_height="match_parent"
 *            android:id="@+id/my_nav_host_fragment"
 *            android:name="androidx.navigation.fragment.NavHostFragment"
 *            app:navGraph="@xml/nav_sample"
 *            app:defaultNavHost="true" /&gt;
 *    &lt;android.support.design.widget.NavigationView
 *            android:layout_width="wrap_content"
 *            android:layout_height="match_parent"
 *            android:layout_gravity="start"/&gt;
 * &lt;/android.support.v4.widget.DrawerLayout&gt;
 * </pre>
 *
 * <p>Each NavHostFragment has a {@link NavController} that defines valid navigation within
 * the navigation host. This includes the {@link NavGraph navigation graph} as well as navigation
 * state such as current location and back stack that will be saved and restored along with the
 * NavHostFragment itself.</p>
 *
 * <p>NavHostFragments register their navigation controller at the root of their view subtree
 * such that any descendant can obtain the controller instance through the {@link Navigation}
 * helper class's methods such as {@link Navigation#findNavController(View)}. View event listener
 * implementations such as {@link android.view.View.OnClickListener} within navigation destination
 * fragments can use these helpers to navigate based on user interaction without creating a tight
 * coupling to the navigation host.</p>
 */
public class NavHostFragment extends Fragment implements NavHost {
    //...
}

参考例子，我们的NavigationMainActivity布局：

 

<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools">
    <android.support.v4.widget.DrawerLayout
        android:id="@+id/drawer_layout"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:fitsSystemWindows="true">
        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:orientation="vertical">

            <android.support.design.widget.AppBarLayout
                android:id="@+id/appbar"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:theme="@style/AppTheme.AppBarOverlay">

                <android.support.v7.widget.Toolbar
                    android:id="@+id/toolbar"
                    android:layout_width="match_parent"
                    android:layout_height="?attr/actionBarSize"
                    app:popupTheme="@style/AppTheme.PopupOverlay"/>

            </android.support.design.widget.AppBarLayout>

            <fragment
                android:id="@+id/garden_nav_fragment"
                android:name="androidx.navigation.fragment.NavHostFragment"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                app:defaultNavHost="true"
                app:navGraph="@navigation/nav_garden"/>
        </LinearLayout>
        <android.support.design.widget.NavigationView
            android:id="@+id/navigation_view"
            style="@style/Widget.MaterialComponents.NavigationView"
            android:layout_width="wrap_content"
            android:layout_height=