Android-Jetpack笔记--Navigation

Navigation

Navigation是Jetpack中一种导航架构，大多是用在管理Fragment上面，不过也可以用来管理Activity,这一节主要是Navigation的入门，写了一个小Demo。

1 首先是需要在app下gradle 添加依赖:

implementation 'androidx.navigation:navigation-fragment:2.2.2'
implementation 'androidx.navigation:navigation-ui:2.2.2'

2 布局:

activity_navigation.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <com.google.android.material.bottomnavigation.BottomNavigationView
        android:id="@+id/nav_view"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginStart="0dp"
        android:layout_marginEnd="0dp"
        android:background="?android:attr/windowBackground"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:menu="@menu/bottom_nav_menu"
        />

    <fragment
        android:id="@+id/nav_host_fragment"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:defaultNavHost="false"
        app:layout_constraintBottom_toTopOf="@id/nav_view"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        />

</androidx.constraintlayout.widget.ConstraintLayout>

说明:这里的android:name="androidx.navigation.fragment.NavHostFragment"是为了使当前的acitivity能够可以加载并使用navigation管理相关的fragment，除了在layout布局中创建外，也可以在activity中添加创建。

3 创建navigation文件

在res目录下创建一个navigation文件夹，新建对应的navigation布局,mobile_navigation如下：

 <?xml version="1.0" encoding="utf-8"?>
<navigation 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:id="@+id/mobile_navigation"
    app:startDestination="@+id/navigation_home"
    >

    <fragment
        android:id="@+id/navigation_home"
        android:name="com.sky.jetpacklearn.navigation.HomeFragment"
        android:label="@string/title_home"
        tools:layout="@layout/fragment_home"
        />

    <fragment
        android:id="@+id/navigation_dashboard"
        android:name="com.sky.jetpacklearn.navigation.DashboardFragment"
        android:label="@string/title_dashboard"
        tools:layout="@layout/fragment_dashboard"
        />
    <fragment
        android:id="@+id/navigation_notification"
        android:name="com.sky.jetpacklearn.navigation.NotificationsFragment"
        android:label="@string/title_notifications"
        tools:layout="@layout/fragment_notifications"
        />

</navigation>

HomeFragment.java(其他两个Fragment类似)

public class HomeFragment extends BaseFragment {
    private HomeViewModel homeViewModel;
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        homeViewModel = ViewModelProviders.of(this).get(HomeViewModel.class);
        View root = inflater.inflate(R.layout.fragment_home, container, false);
        final TextView textView = root.findViewById(R.id.text_home);
        homeViewModel.getText().observe(getViewLifecycleOwner(), new Observer<String>() {
            @Override
            public void onChanged(String s) {
                textView.setText(s);
            }
        });
        return root;
    }
}

fragment_home.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".navigation.HomeFragment">
    <TextView
        android:id="@+id/text_home"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:layout_marginEnd="8dp"
        android:textAlignment="center"
        android:textSize="20sp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        tools:ignore="RtlCompat" />
</androidx.constraintlayout.widget.ConstraintLayout>

import androidx.lifecycle.LiveData;
import androidx.lifecycle.MutableLiveData;
import androidx.lifecycle.ViewModel;

public class HomeViewModel extends ViewModel {
    private MutableLiveData<String> mText;
    public HomeViewModel() {
        mText = new MutableLiveData<>();
        mText.setValue("This is home fragment");
    }
    public LiveData<String> getText() {
        return mText;
    }
}

注:需在gradle添加依赖:

android {
...
buildFeatures{
        dataBinding = true
    }
...
}
    def lifecycle_version = "2.2.0"
    implementation "androidx.lifecycle:lifecycle-common-java8:$lifecycle_version"
    implementation "android.arch.lifecycle:extensions:$lifecycle_version"

FixFragmentNavigator.java

import android.content.Context;
import android.os.Bundle;
import android.util.Log;
import android.view.View;

import androidx.annotation.IdRes;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentManager;
import androidx.fragment.app.FragmentTransaction;
import androidx.navigation.NavDestination;
import androidx.navigation.NavOptions;
import androidx.navigation.Navigator;
import androidx.navigation.fragment.FragmentNavigator;

import java.lang.reflect.Field;
import java.util.ArrayDeque;
import java.util.List;
import java.util.Map;

/**
 * 支持fragment复用的导航器，搜"//fix"可快速定位到修复点
 */
@Navigator.Name("fixFragment")  //fix 5: 需要指定1个名字，源码里自带的名字有navigation、activity、fragment、dialog
public class FixFragmentNavigator extends FragmentNavigator {
    private static final String TAG = "FixFragmentNavigator";
    private Context mContext;
    private FragmentManager mFragmentManager;
    private int mContainerId;

    public FixFragmentNavigator(@NonNull Context context, @NonNull FragmentManager manager, int containerId) {
        super(context, manager, containerId);
        mContext = context;
        mFragmentManager = manager;
        mContainerId = containerId;
    }

    @Nullable
    @Override
    public NavDestination navigate(@NonNull Destination destination, @Nullable Bundle args, @Nullable NavOptions navOptions, @Nullable Navigator.Extras navigatorExtras) {
        if (mFragmentManager.isStateSaved()) {
            Log.i(TAG, "Ignoring navigate() call: FragmentManager has already"
                    + " saved its state");
            return null;
        }
        String className = destination.getClassName();
        if (className.charAt(0) == '.') {
            className = mContext.getPackageName() + className;
        }
        //fix 1: 把类名作为tag，寻找已存在的Fragment
        //（如果想只针对个别fragment进行保活复用，可以在tag上做些标记比如加个前缀）
        Fragment frag = mFragmentManager.findFragmentByTag(className);
        if (null == frag) {
            //不存在，则创建
            frag = instantiateFragment(mContext, mFragmentManager, className, args);
        }

        frag.setArguments(args);
        final FragmentTransaction ft = mFragmentManager.beginTransaction();

        int enterAnim = navOptions != null ? navOptions.getEnterAnim() : -1;
        int exitAnim = navOptions != null ? navOptions.getExitAnim() : -1;
        int popEnterAnim = navOptions != null ? navOptions.getPopEnterAnim() : -1;
        int popExitAnim = navOptions != null ? navOptions.getPopExitAnim() : -1;
        if (enterAnim != -1 || exitAnim != -1 || popEnterAnim != -1 || popExitAnim != -1) {
            enterAnim = enterAnim != -1 ? enterAnim : 0;
            exitAnim = exitAnim != -1 ? exitAnim : 0;
            popEnterAnim = popEnterAnim != -1 ? popEnterAnim : 0;
            popExitAnim = popExitAnim != -1 ? popExitAnim : 0;
            ft.setCustomAnimations(enterAnim, exitAnim, popEnterAnim, popExitAnim);
        }

//        ft.replace(mContainerId, frag);
        //fix 2: replace换成show和hide
        List<Fragment> fragments = mFragmentManager.getFragments();
        for (Fragment fragment : fragments) {
            ft.hide(fragment);
        }
        if (!frag.isAdded()) {
            ft.add(mContainerId, frag, className);
        }
        ft.show(frag);
        ft.setPrimaryNavigationFragment(frag);

        final @IdRes int destId = destination.getId();

        //fix 3: mBackStack是私有的，而且没有暴露出来，只能反射获取
        ArrayDeque<Integer> mBackStack;
        try {
            Field field = FragmentNavigator.class.getDeclaredField("mBackStack");
            field.setAccessible(true);
            mBackStack = (ArrayDeque<Integer>) field.get(this);
        } catch (Exception e) {
            e.printStackTrace();
            return null;
        }

        final boolean initialNavigation = mBackStack.isEmpty();
        final boolean isSingleTopReplacement = navOptions != null && !initialNavigation
                && navOptions.shouldLaunchSingleTop()
                && mBackStack.peekLast() == destId;

        boolean isAdded;
        if (initialNavigation) {
            isAdded = true;
        } else if (isSingleTopReplacement) {
            if (mBackStack.size() > 1) {
                mFragmentManager.popBackStack(
                        generateBackStackName(mBackStack.size(), mBackStack.peekLast()),
                        FragmentManager.POP_BACK_STACK_INCLUSIVE);
                ft.addToBackStack(generateBackStackName(mBackStack.size(), destId));
            }
            isAdded = false;
        } else {
            ft.addToBackStack(generateBackStackName(mBackStack.size() + 1, destId));
            isAdded = true;
        }
        if (navigatorExtras instanceof Extras) {
            Extras extras = (Extras) navigatorExtras;
            for (Map.Entry<View, String> sharedElement : extras.getSharedElements().entrySet()) {
                ft.addSharedElement(sharedElement.getKey(), sharedElement.getValue());
            }
        }
        ft.setReorderingAllowed(true);
        ft.commit();
        if (isAdded) {
            mBackStack.add(destId);
            return destination;
        } else {
            return null;
        }
    }

    //fix 4: 从父类那边copy过来即可
    @NonNull
    private String generateBackStackName(int backStackIndex, int destId) {
        return backStackIndex + "-" + destId;
    }
}

NavigationActivity.java

import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.Fragment;
import androidx.navigation.NavController;
import androidx.navigation.NavGraph;
import androidx.navigation.NavGraphNavigator;
import androidx.navigation.NavigatorProvider;
import androidx.navigation.fragment.FragmentNavigator;
import androidx.navigation.fragment.NavHostFragment;

import android.os.Bundle;

import com.google.android.material.bottomnavigation.BottomNavigationView;
import com.sky.jetpacklearn.R;

public class NavigationActivity extends AppCompatActivity {

    BottomNavigationView navView;
    NavController navController;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_navigation);
        navView = findViewById(R.id.nav_view);

        Fragment fragment = getSupportFragmentManager().findFragmentById(R.id.nav_host_fragment);
        navController = NavHostFragment.findNavController(fragment);
        FixFragmentNavigator fragmentNavigator = new FixFragmentNavigator(this,
                fragment.getChildFragmentManager(),fragment.getId());
        NavigatorProvider provider = navController.getNavigatorProvider();
        provider.addNavigator(fragmentNavigator);
        NavGraph navGraph = initNavGraph(provider, fragmentNavigator);

        //设置导航图
        navController.setGraph(navGraph);
        //底部导航设置点击事件
        navView.setOnNavigationItemSelectedListener(item -> {
            navController.navigate(item.getItemId());
            return true;
        });

    }

    private NavGraph initNavGraph(NavigatorProvider provider,FixFragmentNavigator fragmentNavigator) {
        NavGraph navGraph = new NavGraph(new NavGraphNavigator(provider));

        FragmentNavigator.Destination destination1 = fragmentNavigator.createDestination();
        destination1.setId(R.id.navigation_home);
        destination1.setClassName(HomeFragment.class.getCanonicalName());
        destination1.setLabel(getResources().getString(R.string.title_home));
        navGraph.addDestination(destination1);

        FragmentNavigator.Destination destination2 = fragmentNavigator.createDestination();
        destination2.setId(R.id.navigation_dashboard);
        destination2.setClassName(DashboardFragment.class.getCanonicalName());
        destination2.setLabel(getResources().getString(R.string.title_dashboard));
        navGraph.addDestination(destination2);

        FragmentNavigator.Destination destination3 = fragmentNavigator.createDestination();
        destination3.setId(R.id.navigation_notifications);
        destination3.setClassName(NotificationsFragment.class.getCanonicalName());
        destination3.setLabel(getResources().getString(R.string.title_notifications));
        navGraph.addDestination(destination3);
        navGraph.setStartDestination(R.id.navigation_home);
        return navGraph;
    }

    @Override
    public void onBackPressed() {
        int currentId = navController.getCurrentDestination().getId();
        int startId = navController.getGraph().getStartDestination();
        if(currentId != startId) {
            navView.setSelectedItemId(startId);
        } else {
            finish();
        }
    }
}

以上就是Navigation的主要代码。

Android-Jetpack笔记--Navigation

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