java - 切换到第三个选项卡后 Tabhost 的内容被重置

Question

我正在开发一个带有 3 个选项卡的 Android 应用程序。完成从服务器获取数据后，我将在第一个选项卡中设置文本 Tab1 数据集成功，并且新文本在 View 中可见。然后我切换到tab3并切换回tab1。现在文本是在 tab1.xml 中定义的 Tab 1。那么当我在选项卡之间切换时如何保留以前的 View 内容。

我的安卓代码如下

public class secondPage  extends AppCompatActivity {

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main_screen);
    Intent intent = getIntent();
    String dateStrig = intent.getStringExtra("Date");
    String rData = null;
    TabLayout tabLayout = (TabLayout) findViewById(R.id.tab_layout);
    tabLayout.addTab(tabLayout.newTab().setText("TAB 1"));
    tabLayout.addTab(tabLayout.newTab().setText("TAB 2"));
    tabLayout.addTab(tabLayout.newTab().setText("TAB 3"));
    tabLayout.setTabGravity(TabLayout.GRAVITY_FILL);

    final ViewPager viewPager = (ViewPager) findViewById(R.id.pager);
    final PagerAdapter adapter = new PagerAdapter
            (getSupportFragmentManager(), tabLayout.getTabCount());
    viewPager.setAdapter(adapter);

    new fetchData().execute(dateStrig);


    viewPager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(tabLayout));
    tabLayout.setOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {

        @Override
        public void onTabSelected(TabLayout.Tab tab) {
            viewPager.setCurrentItem(tab.getPosition());
        }

        @Override
        public void onTabUnselected(TabLayout.Tab tab) {

        }

        @Override
        public void onTabReselected(TabLayout.Tab tab) {

        }
    });


}


public class fetchData extends AsyncTask<String, String, String> {

    Logger logger = Logger.getLogger(fetchData.class.getName());

    ProgressDialog progress;

    @Override
    protected void onPreExecute() {
        progress = new ProgressDialog(secondPage.this);
        progress.setMessage("loading...");
        progress.setCancelable(false);
        progress.show();
    }

    @Override
    protected String doInBackground(String... params) {
        String webPage = "", data = "";
        {

            try {
                URL url = new URL("http://192.168.1.101:3000/rate?date=" + params[0]);
                HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
                urlConnection.connect();

                InputStream is = urlConnection.getInputStream();
                BufferedReader reader = new BufferedReader(new InputStreamReader(is, "UTF-8"));


                while ((data = reader.readLine()) != null) {
                    webPage += data + "\n";
                }

                logger.info(webPage);


            } catch (Exception e) {
                e.printStackTrace();
            }


        }
        return webPage;
    }

    protected void onPostExecute(String result) {


        TextView t1=(TextView) findViewById(R.id.textView1);
        t1.setText("Tab 1 selected");
             progress.dismiss();




    }


}
}

PageAdapter.java

public class PagerAdapter extends FragmentStatePagerAdapter {
int mNumOfTabs;

public PagerAdapter(FragmentManager fm, int NumOfTabs) {
    super(fm);
    this.mNumOfTabs = NumOfTabs;
}

@Override
public Fragment getItem(int position) {

    switch (position) {
        case 0:
            Tab1 tab1 = new Tab1();
            return tab1;
        case 1:
            Tab2 tab2 = new Tab2();
            return tab2;
        case 2:
            Tab3 tab3 = new Tab3();
            return tab3;
        default:
            return null;
    }
}

@Override
public int getCount() {
    return mNumOfTabs;
}
}

Tab1.java

public class Tab1 extends Fragment{

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        return inflater.inflate(R.layout.tab1, container, false);
    }
}

Tab2.java

public class Tab2 extends Fragment {

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    return inflater.inflate(R.layout.tab2, container, false);
}
}

Tab3.java

public class Tab3 extends Fragment {

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        return inflater.inflate(R.layout.tab3, container, false);
    }
}

ma​​in_screen.xml

<android.support.design.widget.TabLayout
        android:id="@+id/tab_layout"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@+id/toolbar"
        android:background="?attr/colorPrimary"
        android:elevation="6dp"
        android:minHeight="?attr/actionBarSize"
        android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"/>

<android.support.v4.view.ViewPager
    android:id="@+id/pager"
    android:layout_width="match_parent"
    android:layout_height="fill_parent"
    android:layout_below="@id/tab_layout"/>

tab1.xml

<TextView
    android:id="@+id/textView1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_centerInParent="true"
    android:text="Tab 1"
    android:textAppearance="?android:attr/textAppearanceLarge"/>

tab2.xml 和 tab3.xml 也看起来一样，只是 ID 和文本不同。

Answer 1

这是因为 ViewPager 的离屏行为。默认是 1 次尝试根据您的要求最大化此限制，它对我有用。

_pager.setOffscreenPageLimit(10);