[英]How do I stop fragments from reloading WebView when selected from bottom navigation?
從底部菜單中選擇時,我需要停止刷新每個片段。 這里有很多類似的問題,但是對於 Android 開發來說是新手,我似乎無法工作。 我想我知道它為什么會發生(我相信我正在為每個片段調用 return new )但不確定如何實現略有不同的編碼。 總之,我需要每個選項卡在第一次單擊時加載 WebView,然后保持在 state 中,直到用戶單擊該視圖中的鏈接或關閉應用程序。
MainActivity.java
public class MainActivity extends AppCompatActivity implements BottomNavigationView.OnNavigationItemSelectedListener {
private BottomNavigationView mBottomNavigation;
private ViewPager viewPager;
private ViewPagerAdapter mViewPagerAdapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
loadFragment(new HomeFragment());
mBottomNavigation = findViewById(R.id.nav_view);
mBottomNavigation.setOnNavigationItemSelectedListener(this);
viewPager = findViewById(R.id.view_pager);
mViewPagerAdapter = new ViewPagerAdapter(getSupportFragmentManager());
viewPager.setAdapter(mViewPagerAdapter);
viewPager.setOffscreenPageLimit(5);
}
private boolean loadFragment(Fragment fragment) {
if (fragment != null) {
FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
ft.replace(R.id.container, fragment);
ft.commit();
return true;
}
return false;
}
@Override
public boolean onNavigationItemSelected(MenuItem menuItem) {
Fragment fragment = null;
switch (menuItem.getItemId()) {
case R.id.navigation_news:
fragment = new HomeFragment();
break;
case R.id.navigation_scheduled:
fragment = new DashboardFragment();
break;
case R.id.navigation_LIVE:
fragment = new NotificationsFragment();
break;
case R.id.navigation_results:
fragment = new ResultsFragment();
break;
case R.id.navigation_help:
fragment = new HelpFragment();
break;
}
return loadFragment(fragment);
}}
查看PagerAdapter.java
public class ViewPagerAdapter extends FragmentStatePagerAdapter {
public ViewPagerAdapter(FragmentManager fm){
super(fm);
}
@Override
public Fragment getItem(int position){
switch (position) {
case 0:
return new HomeFragment();
case 1:
return new DashboardFragment();
case 2:
return new NotificationsFragment();
case 3:
return new ResultsFragment();
case 4:
return new HelpFragment();
}
return null;
}
@Override
public int getCount(){
return 5;
}
}
activity_main.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:id="@+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingTop="0dp">
<androidx.viewpager.widget.ViewPager
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="@+id/view_pager"/>
<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:labelVisibilityMode="labeled"
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_activity_main"
android:name="androidx.navigation.fragment.NavHostFragment"
android:layout_width="match_parent"
android:layout_height="0dp"
app:defaultNavHost="true"
app:layout_constraintBottom_toTopOf="@+id/nav_view"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.091"
app:navGraph="@navigation/mobile_navigation"
tools:layout_editor_absoluteX="9dp" />
</androidx.constraintlayout.widget.ConstraintLayout>
首頁Fragment.java
public class HomeFragment extends Fragment {
private HomeViewModel HomeViewModel;
private FragmentHomeBinding binding;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_home, container, false);
String url = "https://www.google.com";
WebView view = (WebView)rootView.findViewById(R.id.webviewnews);
view.getSettings().setJavaScriptEnabled(true);
view.setWebViewClient(new WebViewClient());
view.loadUrl(url);
return rootView;
}
@Override
public void onDestroyView() {
super.onDestroyView();
binding = null;
}
}
先感謝您。
我想這里的問題是每次ViewPagerAdapter.getItem
時都會重新創建每個片段。 每次單擊項目時,都會創建一個新片段。 它不會只是重新加載,它實際上是一個非常新鮮的片段,沒有任何東西。
嘗試懶惰地實例化您的片段,如下所示:
private HomeFragment homeFragment = null;
public Fragment getItem(int position){
switch (position) {
case 0:
if(homeFragment == null) homeFragment = new HomeFragment();
return homeFragment;
// Other cases
這不僅可以幫助您解決問題,而且可以使用更少的 memory 並減少 GC 的壓力。
此外,在你替換之后,你的片段的onResume
將被調用(以防萬一你需要做一些你可以在onResume
中做的事情)
您在加載片段時正在替換片段,因此一旦您調用替換片段,它將重新創建片段並且 onCreate 將被調用,因此關於替換使用添加片段不會一次又一次地重新加載片段
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