我面临以下问题：在主屏幕中，我有 3 个按钮：配置、主要、设置。
- 单击每个按钮时，将显示相应的片段以在 FrameLayout 中膨胀布局。
- 当用户处于 Config 或 Setting Fragment 时，可以使用 onBackpressed 或单击 Main 按钮返回主 Fragment。当用户在主片段中时，如果用户单击返回，则会显示一个弹出窗口以确认退出。
在主片段中，我放了一个查看器。在这个 viewpager 中，我放了另外 2 个片段，每个片段都包含一个图像网格（我还使用了一个圆形指示器来查看底部的页面变化）。为简单起见，Config Fragment 和 Setting Fragment 仅在中心显示一个文本。当应用程序启动时，在正常显示主要片段，当我点击按钮设置或配置时，它正常显示相应的片段。问题是当单击后退按钮（在 Android 上）时，它会返回到主片段，但在 viewpager 中没有片段。它显示空屏幕。
当进程从配置/设置片段返回到主片段时，也许我错了。如果主片段只是在没有 viewpager 的情况下膨胀某个布局，则不会发生此问题。从配置/设置片段返回主片段时如何恢复viewpager的状态？我附上我的代码，以便您可以给我更明确的答案。非常感谢您的任何回答。
package com.example.testfragmentviewpager;
import android.app.AlertDialog;
import android.content.DialogInterface;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.app.FragmentTransaction;
import android.support.v4.view.ViewPager;
import android.view.LayoutInflater;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.view.Window;
import android.widget.Button;
import android.widget.FrameLayout;
import com.example.viewpageindicator.CirclePageIndicator;
import com.example.viewpageindicator.PageIndicator;
public class MainActivity extends FragmentActivity {
Fragment configFragment;
Fragment settingFragment;
Fragment mainItemsFragment;
FrameLayout frmLayout;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
this.requestWindowFeature(Window.FEATURE_NO_TITLE);
setContentView(R.layout.main);
if (savedInstanceState == null) {
FragmentManager fm = getSupportFragmentManager();
FragmentTransaction ft = fm.beginTransaction();
frmLayout = (FrameLayout) findViewById(R.id.frame_cotainer);
mainItemsFragment = new MainItemsFragment();
ft.add(R.id.frame_cotainer, mainItemsFragment, "mainItems").commit();
}
addListener(R.id.btnConfig);
addListener(R.id.btnMain);
addListener(R.id.btnSetting);
}
public void addListener(int buttonID) {
final Button btn = (Button) findViewById(buttonID);
btn.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
showFragment(btn);
}
});
}
public void showFragment(View v) {
FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
switch (v.getId()) {
case R.id.btnConfig:
if (configFragment == null) {
configFragment = new ConfigListFragment();
}
else if (configFragment.isVisible())
return;
if (getCurrentEntriesInBackStack() == 0) {
ft.addToBackStack("mainItems");
}
ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);
ft.replace(R.id.frame_cotainer, configFragment, "config");
break;
case R.id.btnMain:
if (mainItemsFragment == null)
mainItemsFragment = new MainItemsFragment();
if (getCurrentEntriesInBackStack() == 0)
return;
else {
if (configFragment != null && configFragment.isVisible()) {
ft.detach(configFragment);
configFragment = null;
}
if (settingFragment != null && settingFragment.isVisible()) {
ft.detach(settingFragment);
settingFragment = null;
}
ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);
removeFromContainer(ft);
callPopBackStack();
return;
}
case R.id.btnSetting:
if (settingFragment == null)
settingFragment = new SettingFragment();
else if (settingFragment.isVisible())
return;
if (getCurrentEntriesInBackStack() == 0) {
ft.addToBackStack("mainItems");
}
ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);
ft.replace(R.id.frame_cotainer, settingFragment, "setting");
break;
default:
break;
}
ft.commit();
}
private int getCurrentEntriesInBackStack() {
FragmentManager fm = getSupportFragmentManager();
return fm.getBackStackEntryCount();
}
private boolean callPopBackStack() {
FragmentManager fm = getSupportFragmentManager();
boolean result = fm.popBackStackImmediate();
return result;
}
private void removeFromContainer(FragmentTransaction ft) {
if (configFragment != null && configFragment.isVisible()) {
ft.detach(configFragment);
configFragment = null;
}
if (settingFragment != null && settingFragment.isVisible()) {
ft.detach(settingFragment);
settingFragment = null;
}
ft.commit();
}
public static class ConfigListFragment extends Fragment {
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.layout_config, container, false);
return v;
}
}
public static class SettingFragment extends Fragment {
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.layout_setting, container, false);
return v;
}
}
public static class MainItemsFragment extends Fragment {
private MyPagerAdapter adapter;
private ViewPager viewpager;
private PageIndicator mIndicator;
View rootView;
private class setAdapterTask extends AsyncTask<Void, Void, Void> {
protected Void doInBackground(Void... params) {
return null;
}
@Override
protected void onPostExecute(Void result) {
viewpager.setAdapter(adapter);
mIndicator = (CirclePageIndicator) rootView.findViewById(R.id.indicator);
mIndicator.setViewPager(viewpager);
viewpager.setCurrentItem(0);
}
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
rootView = inflater.inflate(R.layout.mainscreen_layout, container, false);
adapter = new MyPagerAdapter(getFragmentManager());
viewpager = (ViewPager) rootView.findViewById(R.id.myviewpager);
new setAdapterTask().execute();
return rootView;
}
}
public static class MyPagerAdapter extends FragmentPagerAdapter {
public MyPagerAdapter(FragmentManager fm) {
super(fm);
}
@Override
public Fragment getItem(int index) {
if (index == 0) {
return new MainFragment1();
}
else {
return new MainFragment2();
}
}
@Override
public int getCount() {
return 2;
}
}
@Override
public void onBackPressed() {
FragmentManager fm = getSupportFragmentManager();
FragmentTransaction ft = fm.beginTransaction();
removeFromContainer(ft);
if (fm.popBackStackImmediate()) {
return;
}
else {
AlertDialog.Builder dlg = new AlertDialog.Builder(MainActivity.this);
dlg.setTitle("Confirm Exit");
dlg.setMessage("Do you want to exit?").setCancelable(false).setPositiveButton("OK", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
MainActivity.this.finish();
}
}).setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
dialog.cancel();
}
});
AlertDialog alertDlg = dlg.create();
alertDlg.show();
}
}
}