android - 你如何防止 fragment webview 每次都重新加载？

Question

我是 Android 应用开发的新手，需要一些帮助。我注意到当我尝试使用带有导航选项卡的 fragment WebView 时，它们的状态保持良好，但是当我切换到使用抽屉导航时，每次我点击一个抽屉项目，然后通过点击返回到那个抽屉项目在我已经加载的抽屉项目上，它只是重新加载 WebView。

MainActivity 代码:

public class MainActivity extends AppCompatActivity
        implements NavigationView.OnNavigationItemSelectedListener {

    NavigationView navigationView = null;
    Toolbar toolbar = null;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        //Set the fragment initially
        MainFragment fragment = new MainFragment();
        android.support.v4.app.FragmentTransaction fragmentTransaction =
                getSupportFragmentManager().beginTransaction();
        fragmentTransaction.replace(R.id.fragment_container, fragment);
        fragmentTransaction.commit();

        toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);


        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);

        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
                this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        drawer.addDrawerListener(toggle);
        toggle.syncState();

        navigationView = (NavigationView) findViewById(R.id.nav_view);

        //How to change elements in the header programatically
        View headerView = navigationView.getHeaderView(0);

        navigationView.setNavigationItemSelectedListener(this);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement


        return super.onOptionsItemSelected(item);
    }

    @SuppressWarnings("StatementWithEmptyBody")
    @Override
    public boolean onNavigationItemSelected(MenuItem item) {
        // Handle navigation view item clicks here.
        int id = item.getItemId();

        if (id == R.id.nav_home) {
            //Set the fragment initially
            MainFragment fragment = new MainFragment();
            android.support.v4.app.FragmentTransaction fragmentTransaction =
                    getSupportFragmentManager().beginTransaction();
            fragmentTransaction.replace(R.id.fragment_container, fragment);
            fragmentTransaction.commit();
            // Handle the camera action
        } else if (id == R.id.nav_store) {
            //Set the fragment initially
            MyStoreFragment fragment = new MyStoreFragment();
            android.support.v4.app.FragmentTransaction fragmentTransaction =
                    getSupportFragmentManager().beginTransaction();
            fragmentTransaction.replace(R.id.fragment_container, fragment);
            fragmentTransaction.commit();

        } else if (id == R.id.nav_blog) {
            //Set the fragment initially
            BlogFragment fragment = new BlogFragment();
            android.support.v4.app.FragmentTransaction fragmentTransaction =
                    getSupportFragmentManager().beginTransaction();
            fragmentTransaction.replace(R.id.fragment_container, fragment);
            fragmentTransaction.commit();

        } else if (id == R.id.nav_billing) {
            //Set the fragment initially
            MyBillingFragment fragment = new MyBillingFragment();
            android.support.v4.app.FragmentTransaction fragmentTransaction =
                    getSupportFragmentManager().beginTransaction();
            fragmentTransaction.replace(R.id.fragment_container, fragment);
            fragmentTransaction.commit();

        } else if (id == R.id.nav_data) {
            //Set the fragment initially
            MyDataFragment fragment = new MyDataFragment();
            android.support.v4.app.FragmentTransaction fragmentTransaction =
                    getSupportFragmentManager().beginTransaction();
            fragmentTransaction.replace(R.id.fragment_container, fragment);
            fragmentTransaction.commit();
        }

        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        drawer.closeDrawer(GravityCompat.START);
        return true;
    }


}

MainFragment(我有其他具有相同设置的 fragment ):

public class MainFragment extends Fragment {


    public MainFragment() {
        // Required empty public constructor
    }

    private static ProgressBar progressBar;
    private static WebView webView;
    private static View v;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        super.onCreate(savedInstanceState);
        v = inflater.inflate(R.layout.fragment_main, container, false);
        progressBar = (ProgressBar) v.findViewById(R.id.progressBar);
        progressBar.setMax(100);
        webView = (WebView) v.findViewById(R.id.webView);

        if(savedInstanceState != null){
            webView.restoreState(savedInstanceState);
        }else{
            webView.getSettings().setJavaScriptEnabled(true);
            webView.getSettings().setSupportZoom(false);
            webView.getSettings().setBuiltInZoomControls(false);
            webView.getSettings().setLoadWithOverviewMode(true);
            webView.getSettings().setUseWideViewPort(true);
            webView.setScrollBarStyle(View.SCROLLBARS_INSIDE_OVERLAY);
            webView.setBackgroundColor(Color.WHITE);

            webView.setWebViewClient(new ourViewClient());

            webView.setWebChromeClient(new WebChromeClient(){
                public void onProgressChanged(WebView view, int progress){
                    progressBar.setProgress(progress);
                    if(progress < 100 && progressBar.getVisibility() == ProgressBar.GONE){
                        progressBar.setVisibility(ProgressBar.VISIBLE);
                        webView.setVisibility(View.GONE);
                    }

                    if(progress == 100){
                        progressBar.setVisibility(ProgressBar.GONE);
                        webView.setVisibility(View.VISIBLE);
                    }
                }
            });

            webView.setOnKeyListener(new OnKeyListener(){
                @Override
                public boolean onKey(View v, int keyCode, KeyEvent event)
                {
                    if(event.getAction() == KeyEvent.ACTION_DOWN)
                    {
                        WebView webView = (WebView) v;

                        switch(keyCode)
                        {
                            case KeyEvent.KEYCODE_BACK:
                                if(webView.canGoBack())
                                {
                                    webView.goBack();
                                    return true;
                                }
                                break;
                        }
                    }

                    return false;
                }
            });

            String data = getActivity().getIntent().getDataString();

            if(Intent.ACTION_VIEW.equals(getActivity().getIntent().getAction())){
                webView.loadUrl(data);
            }else{
                webView.loadUrl("https://someurl");
            }

        }

        return v;
    }

    public class ourViewClient extends WebViewClient {
        @Override
        public void onPageFinished(WebView view, String url){
            super.onPageFinished(view, url);
            view.setVisibility(View.VISIBLE);
            view.bringToFront();
        }

        @Override
        public void onPageStarted(WebView view, String url, Bitmap favicon){
            view.setVisibility(View.GONE);

        }

    }



    @Override
    public void onSaveInstanceState(Bundle outState){
        super.onSaveInstanceState(outState);
        webView.saveState(outState);
    }



}   

Answer 1

这样做

 final   HashMap<String,Fragment> fragment_container = new HashMap<>();
    @SuppressWarnings("StatementWithEmptyBody")
    @Override
    public boolean onNavigationItemSelected(MenuItem item) {
        // Handle navigation view item clicks here.
        int id = item.getItemId();

        if (id == R.id.nav_home) {
            //Set the fragment initially
            MainFragment fragment =fragment_container.get("home");
            if(fragment == null){
                fragment = new MainFragment();
                fragment_container.put("home",fragment);
            }
            android.support.v4.app.FragmentTransaction fragmentTransaction =
                    getSupportFragmentManager().beginTransaction();
            fragmentTransaction.replace(R.id.fragment_container, fragment);
            fragmentTransaction.commit();
            // Handle the camera action
        } else if (id == R.id.nav_store) {
            //Set the fragment initially
            MyStoreFragment fragment =fragment_container.get("store");
            if(fragment == null){
                fragment = new MyStoreFragment();
                fragment_container.put("store",fragment);
            }
            android.support.v4.app.FragmentTransaction fragmentTransaction =
                    getSupportFragmentManager().beginTransaction();
            fragmentTransaction.replace(R.id.fragment_container, fragment);
            fragmentTransaction.commit();

        } else if (id == R.id.nav_blog) {
            //Set the fragment initially

            BlogFragment fragment =fragment_container.get("blog");
            if(fragment == null){
                fragment = new BlogFragment();
                fragment_container.put("blog",fragment);
            }
            android.support.v4.app.FragmentTransaction fragmentTransaction =
                    getSupportFragmentManager().beginTransaction();
            fragmentTransaction.replace(R.id.fragment_container, fragment);
            fragmentTransaction.commit();

        } else if (id == R.id.nav_billing) {
            //Set the fragment initially
            MyBillingFragment fragment = new MyBillingFragment();//finish it yourself like above
            android.support.v4.app.FragmentTransaction fragmentTransaction =
                    getSupportFragmentManager().beginTransaction();
            fragmentTransaction.replace(R.id.fragment_container, fragment);
            fragmentTransaction.commit();

        } else if (id == R.id.nav_data) {
            //Set the fragment initially
            MyDataFragment fragment = new MyDataFragment();//finish it yourself like above
            android.support.v4.app.FragmentTransaction fragmentTransaction =
                    getSupportFragmentManager().beginTransaction();
            fragmentTransaction.replace(R.id.fragment_container, fragment);
            fragmentTransaction.commit();
        }

        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        drawer.closeDrawer(GravityCompat.START);
        return true;
    }

并使用非静态实例缓存您的 View

  private  ProgressBar progressBar;
    private  WebView webView;
    private  View v;
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        super.onCreate(savedInstanceState);
        if(v == null) {
            v = inflater.inflate(R.layout.fragment_main, container, false);
            progressBar = (ProgressBar) v.findViewById(R.id.progressBar);
            progressBar.setMax(100);
            webView = (WebView) v.findViewById(R.id.webView);

            if (savedInstanceState != null) {
                webView.restoreState(savedInstanceState);
            } else {
                webView.getSettings().setJavaScriptEnabled(true);
                webView.getSettings().setSupportZoom(false);
                webView.getSettings().setBuiltInZoomControls(false);
                webView.getSettings().setLoadWithOverviewMode(true);
                webView.getSettings().setUseWideViewPort(true);
                webView.setScrollBarStyle(View.SCROLLBARS_INSIDE_OVERLAY);
                webView.setBackgroundColor(Color.WHITE);

                webView.setWebViewClient(new ourViewClient());

                webView.setWebChromeClient(new WebChromeClient() {
                    public void onProgressChanged(WebView view, int progress) {
                        progressBar.setProgress(progress);
                        if (progress < 100 && progressBar.getVisibility() == ProgressBar.GONE) {
                            progressBar.setVisibility(ProgressBar.VISIBLE);
                            webView.setVisibility(View.GONE);
                        }

                        if (progress == 100) {
                            progressBar.setVisibility(ProgressBar.GONE);
                            webView.setVisibility(View.VISIBLE);
                        }
                    }
                });

                webView.setOnKeyListener(new OnKeyListener() {
                    @Override
                    public boolean onKey(View v, int keyCode, KeyEvent event) {
                        if (event.getAction() == KeyEvent.ACTION_DOWN) {
                            WebView webView = (WebView) v;

                            switch (keyCode) {
                                case KeyEvent.KEYCODE_BACK:
                                    if (webView.canGoBack()) {
                                        webView.goBack();
                                        return true;
                                    }
                                    break;
                            }
                        }

                        return false;
                    }
                });

                String data = getActivity().getIntent().getDataString();

                if (Intent.ACTION_VIEW.equals(getActivity().getIntent().getAction())) {
                    webView.loadUrl(data);
                } else {
                    webView.loadUrl("https://someurl");
                }

            }
        }

        return v;
    }