android - 在抽屉导航中单击项目时在 viewpager 中切换 fragment

Question

即使在 Stack Overflow 上看到了很多问题，我也没有得到正确的答案，因此写下了这篇文章。我在 View 寻呼机中创建了一个选项卡布局。

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

    <android.support.design.widget.CoordinatorLayout
        android:id="@+id/main_content"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <android.support.design.widget.AppBarLayout
            android:id="@+id/appbar"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar">

            <android.support.v7.widget.Toolbar
                android:id="@+id/toolbar"
                android:layout_width="match_parent"
                android:layout_height="?attr/actionBarSize"
                android:background="?attr/colorPrimary"
                app:layout_scrollFlags="scroll|enterAlways"
                app:popupTheme="@style/ThemeOverlay.AppCompat.Light" />

            <android.support.design.widget.TabLayout
                android:id="@+id/tabs"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                app:tabGravity="fill"
                app:tabMode="scrollable"
                app:tabTextAppearance="@style/TabTextAppearance"/>
        </android.support.design.widget.AppBarLayout>
        <android.support.v4.view.ViewPager
            android:id="@+id/viewpager"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            app:layout_behavior="@string/appbar_scrolling_view_behavior" />

    </android.support.design.widget.CoordinatorLayout>
    <android.support.design.widget.NavigationView
        android:id="@+id/nav_view"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:layout_gravity="start"
        android:fitsSystemWindows="true"
        app:headerLayout="@layout/navheader"
        app:menu="@menu/menu_navigation" />
</android.support.v4.widget.DrawerLayout>

我已经从 Google Code Lab Material Design 编写了这个代码。我的基本要求:

View 分页器中有六个选项卡或 fragment 。相应的六个选项也会出现在拉动抽屉导航时。当我单击抽屉中的某个项目时说项目编号 4，从当前选项卡或 fragment 到相应的第 4 个选项卡或 fragment 必须有一个沼泽。

我主要 Activity 中的代码:

 protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        // Adding Toolbar to Main screen
        mHandler = new Handler();
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        // Setting ViewPager for each Tabs
        ViewPager viewPager = (ViewPager) findViewById(R.id.viewpager);
        setupViewPager(viewPager);
        // Set Tabs inside Toolbar
        TabLayout tabs = (TabLayout) findViewById(R.id.tabs);
        tabs.setupWithViewPager(viewPager);
        // Create Navigation drawer and inlfate layout
        NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
        mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer);
        // Adding menu icon to Toolbar
        ActionBar supportActionBar = getSupportActionBar();
        if (supportActionBar != null) {
            VectorDrawableCompat indicator =
                    VectorDrawableCompat.create(getResources(), R.drawable.ic_menu, getTheme());
            indicator.setTint(ResourcesCompat.getColor(getResources(), R.color.white, getTheme()));
            supportActionBar.setHomeAsUpIndicator(indicator);
            supportActionBar.setDisplayHomeAsUpEnabled(true);
        }
        // Set behavior of Navigation drawer
        navigationView.setNavigationItemSelectedListener(
                new NavigationView.OnNavigationItemSelectedListener() {
                    // This method will trigger on item Click of navigation menu

//                    public boolean onNavigationItemSelected(MenuItem menuItem) {
//                        // Set item in checked state
//                        menuItem.setChecked(true);
//
//                        // TODO: handle navigation
//
//                        // Closing drawer on item click
//                        mDrawerLayout.closeDrawers();
//                        return true;
//                    }


                    @Override
                    public boolean onNavigationItemSelected(MenuItem menuItem) {

                        //Check to see which item was being clicked and perform appropriate action
                        switch (menuItem.getItemId()) {
                            //Replacing the main content with ContentFragment Which is our Inbox View;
                            case R.id.nav_home:
                                navItemIndex = 0;
                                CURRENT_TAG = TAG_HOME;
                                break;
                            case R.id.nav_history:
                                navItemIndex = 1;
                                CURRENT_TAG = TAG_HISTORY;
                                break;
                            case R.id.nav_location:
                                navItemIndex = 2;
                                CURRENT_TAG = TAG_LOCATION;
                                break;
                            case R.id.nav_developments:
                                navItemIndex = 3;
                                CURRENT_TAG = TAG_DEVELOPMENTS;
                                break;
                            case R.id.nav_donations:
                                navItemIndex = 4;
                                CURRENT_TAG = TAG_DONATIONS;
                                break;
                            case R.id.nav_resources:
                                navItemIndex = 5;
                                CURRENT_TAG = TAG_RESOURCES;
                                break;
                            case R.id.nav_feedback:
                                navItemIndex = 6;
                                CURRENT_TAG = TAG_FEEDBACK;
                                break;
                            case R.id.nav_contactus:
                                navItemIndex = 7;
                                CURRENT_TAG = TAG_CONTACTUS;
                                break;

                            default:
                                navItemIndex = 0;
                        }

                        //Checking if the item is in checked state or not, if not make it in checked state
                        if (menuItem.isChecked()) {
                            menuItem.setChecked(false);
                        } else {
                            menuItem.setChecked(true);
                        }
                        menuItem.setChecked(true);

                        loadHomeFragment();

                        return true;
                    }
                });
        // Adding Floating Action Button to bottom right of main view

    }

    private void loadHomeFragment() {

        // if user select the current navigation menu again, don't do anything
        // just close the navigation drawer
        if (getSupportFragmentManager().findFragmentByTag(CURRENT_TAG) != null) {
            mDrawerLayout.closeDrawers();

            // show or hide the fab button

            return;
        }

        // Sometimes, when fragment has huge data, screen seems hanging
        // when switching between navigation menus
        // So using runnable, the fragment is loaded with cross fade effect
        // This effect can be seen in GMail app
        Runnable mPendingRunnable = new Runnable() {
            @Override
            public void run() {
                // update the main content by replacing fragments



                Fragment fragment = getHomeFragment();
                FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();

                fragmentTransaction.replace(R.id.viewpager, fragment, CURRENT_TAG);
                fragmentTransaction.commitAllowingStateLoss();
            }
        };

        // If mPendingRunnable is not null, then add to the message queue
        if (mPendingRunnable != null) {
            mHandler.post(mPendingRunnable);
        }

        // show or hide the fab button


        //Closing drawer on item click
        mDrawerLayout.closeDrawers();


    }



    private Fragment getHomeFragment() {
        switch (navItemIndex) {
            case 0:
                // home
                one_main oneMain = new one_main();
                return oneMain;
            case 1:
                // photos
                one_fragment oneFragment = new one_fragment();
                return oneFragment;
            case 2:
                // movies fragment
                two_location twoLocation = new two_location();
                return twoLocation;
            case 3:
                // notifications fragment
                four_future fourFuture = new four_future();
                return fourFuture;

            case 4:
                // settings fragment
                three_donation threeDonation = new three_donation();
                return threeDonation;

            case 5:
                // movies fragment
                six_download sixDownload = new six_download();
                return sixDownload;
            case 6:
                // notifications fragment
                five_feedback fiveFeedback = new five_feedback();
                return fiveFeedback;

            case 7:
                // settings fragment
                seven_contact sevenContact = new seven_contact();
                return sevenContact;
            default:
                return new one_main();
        }
    }

我可以打开我的应用程序。我能够在选项卡之间导航。我能够拉出抽屉布局。但是，当我单击抽屉中的任何项目时，会切换到相应的选项卡。但是选项卡中的所有内容都变空了。如何解决？

或者在Drawer Layout中点击item的fragment switching有什么更好的解决方案吗？如果是，请指出详细教程。

Answer 1

我使用下面的代码解决了这个问题:

viewPager.setCurrentItem(navItemIndex)

在navigationView.setNavigationItemSelectedListener中