Android Tabview + Webview

I want to make the webview content change (url change) when tab is changed.
However, my code is late. When I change tabs, it shows the last tab's content.

For example,<br/>
App Initialize -> shows first tab and first tab's webview (success)<br/>
Click Tab 2 -> shows second tab but first tab's webview (fail)<br/>
Click Tab 3 -> shows third tab but first tab's webview (fail)<br/>
Return to Tab 2 -> shows second tab and second tab's webview (success)<br/>

Please help.

MainActivity.java

public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
SectionsPagerAdapter sectionsPagerAdapter = new SectionsPagerAdapter(this, getSupportFragmentManager());
final ViewPager viewPager = findViewById(R.id.view_pager);
viewPager.setAdapter(sectionsPagerAdapter);
TabLayout tabs = findViewById(R.id.tabs);
tabs.setupWithViewPager(viewPager);
tabs.setOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
@Override
public void onTabSelected(TabLayout.Tab tab) {
}
@Override
public void onTabUnselected(TabLayout.Tab tab) {
}
@Override
public void onTabReselected(TabLayout.Tab tab) {
}
});
}
}

SectionsPagerAdapter.java

/**
* A [FragmentPagerAdapter] that returns a fragment corresponding to
* one of the sections/tabs/pages.
*/
public class SectionsPagerAdapter extends FragmentPagerAdapter {
@StringRes
private static final int[] TAB_TITLES = new int[]{R.string.tab_text_1, R.string.tab_text_2, R.string.tab_text_3, R.string.tab_text_4, R.string.tab_text_5, R.string.tab_text_6, R.string.tab_text_7};
private final Context mContext;
public SectionsPagerAdapter(Context context, FragmentManager fm) {
super(fm);
mContext = context;
}
@Override
public Fragment getItem(int position) {
// getItem is called to instantiate the fragment for the given page.
// Return a PlaceholderFragment (defined as a static inner class below).
return PlaceholderFragment.newInstance(position + 1);
}
@Nullable
@Override
public CharSequence getPageTitle(int position) {
return mContext.getResources().getString(TAB_TITLES[position]);
}
@Override
public int getCount() {
// Show 2 total pages.
return 7;
}
}

PlaceholderFragment.java

/**
* A placeholder fragment containing a simple view.
*/
public class PlaceholderFragment extends Fragment {
String type;
private static final String ARG_SECTION_NUMBER = "section_number";
private PageViewModel pageViewModel;
public static PlaceholderFragment newInstance(int index) {
PlaceholderFragment fragment = new PlaceholderFragment();
Bundle bundle = new Bundle();
bundle.putInt(ARG_SECTION_NUMBER, index);
fragment.setArguments(bundle);
return fragment;
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
pageViewModel = ViewModelProviders.of(this).get(PageViewModel.class);
int index = 1;
if (getArguments() != null) {
index = getArguments().getInt(ARG_SECTION_NUMBER);
}
pageViewModel.setIndex(index);
}
@Override
public View onCreateView(
@NonNull LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View root = inflater.inflate(R.layout.fragment_main, container, false);
final WebView webView = (WebView)root.findViewById(R.id.webView);
webView.setWebViewClient( new WebViewClient(){
@Override
public boolean shouldOverrideUrlLoading(WebView view, String url){
webView.loadUrl(url);
return true;
}
});
webView.getSettings().setJavaScriptEnabled(true);
webView.getSettings().setRenderPriority(WebSettings.RenderPriority.HIGH);
pageViewModel.getText().observe(this, new Observer<String>() {
@Override
public void onChanged(@Nullable String s) {
type = s;
}
});
if(type == null)
{
type="1";
}
webView.loadUrl("https://my.domain/list.php?type="+type);
return root;
}
}

PageViewModel.java

public class PageViewModel extends ViewModel {
private MutableLiveData<Integer> mIndex = new MutableLiveData<>();
private LiveData<String> mText = Transformations.map(mIndex, new Function<Integer, String>() {
@Override
public String apply(Integer input) {
return input.toString();
}
});
public void setIndex(int index) {
mIndex.setValue(index);
}
public LiveData<String> getText() {
return mText;
}
}

You can add a loader till the webview loads in respective tabs. onPageFinished() is a callback when webview has completed loading

web_view.webViewClient = object : WebViewClient() {
override fun onPageFinished(view: WebView, weburl: String) {
// Stop loading
}
}
</details>
# 答案2
**得分**: 0
我的建议是你应该将以下代码更改：
```lang-java
webView.loadUrl("https://my.domain/list.php?type=" + getArguments().getInt(ARG_SECTION_NUMBER));

并观察它的工作情况。如果它按照你的预期工作，我认为你可能根本不需要 PageViewModel.java。

异常行为的根本原因

在 PageViewModel 中，mIndex 的值通过 PlaceholderFragment 中 onCreate 中的以下行进行更新：

pageViewModel.setIndex(index);

它还改变了 mText 的值，而这个值在 PlaceholderFragment 中的 onCreateView 中的以下块中被观察：

pageViewModel.getText().observe(this, new Observer<String>() {
@Override
public void onChanged(@Nullable String s) {
type = s;
}
});

因此，PageViewModel 和 PlaceholderFragment 出现了意外的竞争。

ViewPager 在早期创建了更多的 Fragment，正如 setOffscreenPageLimit 中所写。在 PlaceholderFragment 的 onCreate 中更新 mIndex 的值不是一个好主意。

webView.loadUrl("https://my.domain/list.php?type="+type);

webView.loadUrl("https://my.domain/list.php?type=" + getArguments().getInt(ARG_SECTION_NUMBER));

pageViewModel.setIndex(index);

pageViewModel.getText().observe(this, new Observer<String>() {
@Override
public void onChanged(@Nullable String s) {
type = s;
}
});