定制的Fragment导航器，替换ft.replace(mCon

1.对destination.json通过GsonFormat进行变成对象
2.编写AppConfig工具类对destination.json解释成HashMap
3.创建FixFragmentNavigator
4.创建NavGraphBuilder

1.对destination.json通过GsonFormat进行变成对象

{
  "main/tabs/home": {
    "isFragment": true,
    "asStarter": true,
    "needLogin": false,
    "pageUrl": "main/tabs/home",
    "className": "com.mooc.ppjoke.ui.home.HomeFragment",
    "id": 946010952
  }
}

public class Destination {
    /**
     * isFragment : true
     * asStarter : true
     * needLogin : false
     * pageUrl : main/tabs/home
     * className : com.mooc.ppjoke.ui.home.HomeFragment
     * id : 946010952
     */
    public boolean isFragment;
    public boolean asStarter;
    public boolean needLogin;
    public String pageUrl;
    public String className;
    public int id;
}

2.编写AppConfig工具类对destination.json解释成HashMap

import android.content.res.AssetManager;
import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.TypeReference;
import com.mooc.libcommon.global.AppGlobals;
import com.mooc.ppjoke.model.Destination;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;

public class AppConfig {
    private static HashMap<String, Destination> sDestConfig;

    public static HashMap<String, Destination> getDestConfig() {
        if (sDestConfig == null) {
            String content = parseFile("destination.json");
            sDestConfig = JSON.parseObject(content, new TypeReference<HashMap<String, Destination>>() {
            });
        }
        return sDestConfig;
    }

    private static String parseFile(String fileName) {
        AssetManager assets = AppGlobals.getApplication().getAssets();
        InputStream is = null;
        BufferedReader br = null;
        StringBuilder builder = new StringBuilder();
        try {
            is = assets.open(fileName);
            br = new BufferedReader(new InputStreamReader(is));
            String line = null;
            while ((line = br.readLine()) != null) {
                builder.append(line);
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if (is != null) {
                    is.close();
                }
                if (br != null) {
                    br.close();
                }
            } catch (Exception e) {

            }
        }

        return builder.toString();
    }
}

3.创建FixFragmentNavigator

/**
 * 定制的Fragment导航器，替换ft.replace(mContainerId, frag);为 hide()/show()
 */
@Navigator.Name("fixfragment")
public class FixFragmentNavigator extends FragmentNavigator {
    private static final String TAG = "FixFragmentNavigator";
    private Context mContext;
    private FragmentManager mManager;
    private int mContainerId;

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

    @Nullable
    @Override
    public NavDestination navigate(@NonNull Destination destination, @Nullable Bundle args, @Nullable NavOptions navOptions, @Nullable Navigator.Extras navigatorExtras) {
        if (mManager.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;
        }
        //android.fragment.app.homefragment   homefragment
        String tag = className.substring(className.lastIndexOf(".") + 1);
        Fragment frag = mManager.findFragmentByTag(tag);
        if (frag == null) {
            frag = instantiateFragment(mContext, mManager,
                    className, args);
        }
        frag.setArguments(args);
        final FragmentTransaction ft = mManager.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);
        }

        List<Fragment> fragments = mManager.getFragments();
        for (Fragment fragment : fragments) {
            ft.hide(fragment);
        }
        if (!frag.isAdded()) {
            ft.add(mContainerId, frag, tag);
        }
        ft.show(frag);
        //ft.replace(mContainerId, frag);
        ft.setPrimaryNavigationFragment(frag);

        final @IdRes int destId = destination.getId();
        ArrayDeque<Integer> mBackStack = null;
        try {
            Field field = FragmentNavigator.class.getDeclaredField("mBackStack");
            field.setAccessible(true);
            mBackStack = (ArrayDeque<Integer>) field.get(this);
        } catch (NoSuchFieldException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        }

        final boolean initialNavigation = mBackStack.isEmpty();
        // TODO Build first class singleTop behavior for fragments
        final boolean isSingleTopReplacement = navOptions != null && !initialNavigation
                && navOptions.shouldLaunchSingleTop()
                && mBackStack.peekLast() == destId;

        boolean isAdded;
        if (initialNavigation) {
            isAdded = true;
        } else if (isSingleTopReplacement) {
            // Single Top means we only want one instance on the back stack
            if (mBackStack.size() > 1) {
                // If the Fragment to be replaced is on the FragmentManager's
                // back stack, a simple replace() isn't enough so we
                // remove it from the back stack and put our replacement
                // on the back stack in its place
                mManager.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();
        // The commit succeeded, update our view of the world
        if (isAdded) {
            mBackStack.add(destId);
            return destination;
        } else {
            return null;
        }
    }

    private String generateBackStackName(int backStackindex, int destid) {
        return backStackindex + "-" + destid;
    }
}

4.创建NavGraphBuilder

import android.content.ComponentName;

import androidx.fragment.app.FragmentActivity;
import androidx.fragment.app.FragmentManager;
import androidx.navigation.ActivityNavigator;
import androidx.navigation.NavController;
import androidx.navigation.NavGraph;
import androidx.navigation.NavGraphNavigator;
import androidx.navigation.NavigatorProvider;
import androidx.navigation.fragment.FragmentNavigator;

import com.mooc.libcommon.global.AppGlobals;
import com.mooc.ppjoke.navigator.FixFragmentNavigator;
import com.mooc.ppjoke.model.Destination;

import java.util.HashMap;
import java.util.Iterator;

public class NavGraphBuilder {
    public static void build(FragmentActivity activity, FragmentManager childFragmentManager, NavController controller, int containerId) {
        NavigatorProvider provider = controller.getNavigatorProvider();

        //NavGraphNavigator也是页面路由导航器的一种，只不过他比较特殊。
        //它只为默认的展示页提供导航服务,但真正的跳转还是交给对应的navigator来完成的
        NavGraph navGraph = new NavGraph(new NavGraphNavigator(provider));

        //FragmentNavigator fragmentNavigator = provider.getNavigator(FragmentNavigator.class);
        //fragment的导航此处使用我们定制的FixFragmentNavigator，底部Tab切换时 使用hide()/show(),而不是replace()
        FixFragmentNavigator fragmentNavigator = new FixFragmentNavigator(activity, childFragmentManager, containerId);
        provider.addNavigator(fragmentNavigator);
        ActivityNavigator activityNavigator = provider.getNavigator(ActivityNavigator.class);
        HashMap<String, Destination> destConfig = AppConfig.getDestConfig();
        Iterator<Destination> iterator = destConfig.values().iterator();
        while (iterator.hasNext()) {
            Destination node = iterator.next();
            if (node.isFragment) {
                FixFragmentNavigator.Destination destination = fragmentNavigator.createDestination();
                destination.setId(node.id);
                destination.setClassName(node.className);
                destination.addDeepLink(node.pageUrl);
                navGraph.addDestination(destination);
            } else {
                ActivityNavigator.Destination destination = activityNavigator.createDestination();
                destination.setId(node.id);
                destination.setComponentName(new ComponentName(AppGlobals.getApplication().getPackageName(), node.className));
                destination.addDeepLink(node.pageUrl);
                navGraph.addDestination(destination);
            }

            //给APP页面导航结果图 设置一个默认的展示页的id
            if (node.asStarter) {
                navGraph.setStartDestination(node.id);
            }
        }

        controller.setGraph(navGraph);
    }
}