14

我正在尝试创建一个使用 Jack Wharton 的 ViewPager 库（此处）的应用程序，每个页面仅使用图像（类似于 Prixing（此处）主屏幕）。一切正常，除了片段中的 saveInstance。

在 Jack Wharton 的示例中，他将文本存储在一个名为 mContent 的 String 变量中，并在 onCreate 中恢复它，但在我的情况下，我该怎么办？保存/恢复位图？！任何客观的答案将不胜感激！

我对这个使用应用程序的 Fragment 很陌生，因为我看到的每个示例都只介绍了基础知识，而对于更复杂的示例则变得越来越困难。

PS。如果知道有用的话，我正在使用 CirclePageIndicator。

当前的片段代码在这里：

    public final class SpecialOfferFragment extends Fragment {

    private int imageResourceId;

    public static SpecialOfferFragment newInstance(int i) {

        //probably I'll use a bitmap(downloaded) as parameter instead of using static images
        SpecialOfferFragment fragment = new SpecialOfferFragment();

        fragment.imageResourceId = i;

        return fragment;
    }


    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        // if ((savedInstanceState != null) { }

    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {

        ImageView image = new ImageView(getActivity());
        image.setImageResource(imageResourceId);
        image.setScaleType(ScaleType.FIT_XY);

        LinearLayout layout = new LinearLayout(getActivity());
        layout.setLayoutParams(new LayoutParams(LayoutParams.FILL_PARENT,
                LayoutParams.FILL_PARENT));

        layout.setGravity(Gravity.CENTER);
        layout.addView(image);

        return layout;
    }

    @Override
    public void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        //smth to save here..
    }
}

在应用程序的当前状态下，我收到以下异常：

04-12 07:28:17.760: E/AndroidRuntime(31903): FATAL EXCEPTION: main 
04-12 07:28:17.760: E/AndroidRuntime(31903): java.lang.NullPointerException
04-12 07:28:17.760: E/AndroidRuntime(31903): at android.support.v4.app.FragmentManagerImpl.saveFragmentBasicState(FragmentManager.java:1576)
04-12 07:28:17.760: E/AndroidRuntime(31903):    at android.support.v4.app.FragmentManagerImpl.saveAllState(FragmentManager.java:1617)
04-12 07:28:17.760: E/AndroidRuntime(31903):    at android.support.v4.app.FragmentActivity.onSaveInstanceState(FragmentActivity.java:481)
04-12 07:28:17.760: E/AndroidRuntime(31903):    at android.app.Activity.performSaveInstanceState(Activity.java:1113)
04-12 07:28:17.760: E/AndroidRuntime(31903):    at android.app.Instrumentation.callActivityOnSaveInstanceState(Instrumentation.java:1188)
04-12 07:28:17.760: E/AndroidRuntime(31903):    at android.app.ActivityThread.performStopActivityInner(ActivityThread.java:2804)
04-12 07:28:17.760: E/AndroidRuntime(31903):    at android.app.ActivityThread.handleStopActivity(ActivityThread.java:2862)
04-12 07:28:17.760: E/AndroidRuntime(31903):    at android.app.ActivityThread.access$900(ActivityThread.java:127)
04-12 07:28:17.760: E/AndroidRuntime(31903):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1175)
04-12 07:28:17.760: E/AndroidRuntime(31903):    at android.os.Handler.dispatchMessage(Handler.java:99)
04-12 07:28:17.760: E/AndroidRuntime(31903):    at android.os.Looper.loop(Looper.java:137)
04-12 07:28:17.760: E/AndroidRuntime(31903):    at android.app.ActivityThread.main(ActivityThread.java:4511)
04-12 07:28:17.760: E/AndroidRuntime(31903):    at java.lang.reflect.Method.invokeNative(Native Method)
04-12 07:28:17.760: E/AndroidRuntime(31903):    at java.lang.reflect.Method.invoke(Method.java:511)
04-12 07:28:17.760: E/AndroidRuntime(31903):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:980)
04-12 07:28:17.760: E/AndroidRuntime(31903):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:747)
04-12 07:28:17.760: E/AndroidRuntime(31903):    at dalvik.system.NativeStart.main(Native Method)

每当我暂停/停止包含此片段的活动时，都会发生这种情况，例如按下主页按钮。

**

编辑代码：

**

 public class MainMenu extends FragmentActivity {

    //private List<CategoriesHolder> categoriesList = new ArrayList<CategoriesHolder>();
    //private CategoriesAdapter categoriesAdapter = null;
    //private GridView gv_mainmenu_categories;

    SpecialOfferFragmentAdapter mAdapter;
    ViewPager mPager;
    PageIndicator mIndicator;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_mainmenu);

        linkUI();
        setAction();

        // just for testing
        String[] imagesUrls = null;

        mAdapter = new SpecialOfferFragmentAdapter(getSupportFragmentManager(),
                this, imagesUrls);

        //categoriesAdapter = new CategoriesAdapter(this, categoriesList);

        // used for Categories GridView
        //gv_mainmenu_categories.setAdapter(categoriesAdapter);

        // used for ViewPager
        mPager.setAdapter(mAdapter);
        mIndicator.setViewPager(mPager);

    }

    private void linkUI() {
        mPager = (ViewPager) findViewById(R.id.vp_mainmenu_special_offers);
        mIndicator = (CirclePageIndicator) findViewById(R.id.indicator);

        //gv_mainmenu_categories = (GridView) findViewById(R.id.gv_mainmenu_categories);

    }

    private void setAction() {

    }
} 

    public class SpecialOfferFragmentAdapter extends FragmentPagerAdapter implements
        IconPagerAdapter {

    private int[] mCarouselImages = new int[] { R.drawable.pic1,
            R.drawable.pic2, R.drawable.pic3, R.drawable.pic4, R.drawable.pic5

    };

    private String[] imagesUrls;
    private Context context;

    public static final int[] ICONS = new int[] {
            R.drawable.perm_group_calendar, R.drawable.perm_group_camera,
            R.drawable.perm_group_device_alarms, R.drawable.perm_group_location };

    private int mCount = mCarouselImages.length;

    public SpecialOfferFragmentAdapter(FragmentManager fm, Context context,
            String[] imagesUrls) {
        super(fm);
        this.context = context;
        this.imagesUrls = imagesUrls;
    }

    @Override
    public Fragment getItem(int position) {

        return SpecialOfferFragment.newInstance(mCarouselImages[position]);
    }

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

    @Override
    public int getIconResId(int index) {
        return ICONS[index % ICONS.length];
    }

    public void setCount(int count) {
        if (count > 0 && count <= 10) {
            mCount = count;
            notifyDataSetChanged();
        }
    }
}
4

6 回答 6

11

为了实现你想要的东西，你应该使用整数值来存储你的当前位置ViewPager，然后使用这个值来设置你的正确位置ViewPager。

例如在你的做这样的事情FragmentActivity：

@Override
public void onSaveInstanceState(Bundle savedInstanceState) {
  super.onSaveInstanceState(savedInstanceState);
  savedInstanceState.putInt("mMyCurrentPosition", mPager.getPosition());
}

@Override
public void onRestoreInstanceState(Bundle savedInstanceState) {
  super.onRestoreInstanceState(savedInstanceState);
  mMyCurrentPosition = savedInstanceState.getInt("mMyCurrentPosition");
  // where mMyCurrentPosition should be a public value in your activity.
}

这将保存您的 ViewPager 的最后一个位置。然后在你onResume()的例子之后你可以检查

if(mMyCurrentPosition != 0){
    mPager.setCurrentItem(mMyCurrentPosition);
}

我认为这应该可行，将图像/位图保存在捆绑包中不是一个好习惯（而且我认为你做不到）。

于 2013-04-12T08:40:45.947 回答
2

好的，首先我想澄清一些可能解决您对已保存实例状态的困惑的东西。Savedinstancestate 只能处理原语（int、double、float、byte..）和 String 对象。这应该是您所需要的，但在某些情况下，您还想保存其他对象的实例。为此，您需要一些其他模式来完成这项工作，例如一个工厂模式，其中包含所有位图的数组。例如，创建一个类 ImageFactory 来保存位图的静态 ArrayList。每当您旋转设备时，都会再次调用 oncreateview 和 onactivitycreated 方法，此时您可以检查是否要从工厂检索信息。例如

if(savedInstanceState != null) { //我们有一个 savedinstancestate 所以可能有保存的图像 ImageFactory.getBMPs(); }

希望你能用这个信息做点什么。祝你好运

于 2013-04-12T07:36:12.843 回答
2

这在您的主要活动中对我来说既简单又简单

 @Override
    protected void onRestoreInstanceState(Bundle savedInstanceState) {
        super.onRestoreInstanceState(savedInstanceState);
        onCreate(savedInstanceState);
    }

在你的清单里面

 <activity
            android:configChanges="orientation|screenSize"/>
于 2016-01-23T04:20:14.590 回答
1

我创建了我自己的方法来保存片段数据，同时使用 SharedPreference 更改选项卡：

方法如：

  public void saveData() {

    Log.d("msg", "Save Instance");
    SharedPreferences.Editor outState = getActivity().getSharedPreferences("order", Context.MODE_APPEND).edit();

    orderDate = orderDateEditText.getText().toString();
    orderBy = orderByEditText.getText().toString();
    orderMobileNo = orderMobileNoEditText.getText().toString();
    orderTransport = orderTransportEditText.getText().toString();
    orderInvoicePer = orderInvoicePerEditText.getText().toString(); 
    orderCharge = orderChargeEditText.getText().toString();
    orderGoodsDispatch = orderGoodsDispatchEditText.getText().toString();
    orderOthers = orderOthersEditText.getText().toString();
    orderIsDirect = orderIsDirectCheckBox.isChecked() ? 1 : 0;

    outState.putBoolean("saved", true);

    outState.putString("orderDate", orderDate);
    outState.putString("orderBy", orderBy);
    outState.putString("orderMobileNo", orderMobileNo);
    outState.putString("orderTransport", orderTransport);
    outState.putString("orderInvoicePer", orderInvoicePer);
    outState.putString("orderCharge", orderCharge);
    outState.putString("orderGoodsDispatch", orderGoodsDispatch);
    outState.putString("orderOthers", orderOthers);
    outState.putInt("orderIsDirect", orderIsDirect);

    outState.commit();
}

调用此方法时

    @Override
    public void onStop() {
    // TODO Auto-generated method stub
        super.onStop();

        saveData();
}

用EditText替换保存的数据：

@Override
public void onActivityCreated(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onActivityCreated(savedInstanceState);

    /***** PUT DATA IN EDITTEXT is ITS AVAILABLE IN BUNDLE *****/
    SharedPreferences orderData = getActivity().getSharedPreferences("order", Context.MODE_APPEND);
    Log.d("msg", ""+orderData.getBoolean("saved", false));

    if(orderData.getBoolean("saved", false))
    {
        orderDate = orderData.getString("orderDate", "");
        orderBy = orderData.getString("orderBy", "");
        orderMobileNo = orderData.getString("orderMobileNo", "");
        orderTransport = orderData.getString("orderTransport", "");
        orderInvoicePer = orderData.getString("orderInvoicePer", ""); 
        orderCharge = orderData.getString("orderCharge", "");
        orderGoodsDispatch = orderData.getString("orderGoodsDispatch", "");
        orderOthers = orderData.getString("orderOthers", "");
        orderIsDirect = orderData.getInt("orderIsDirect", 0);

        orderDateEditText.setText(orderDate);
        orderByEditText.setText(orderBy);
        orderMobileNoEditText.setText(orderMobileNo);
        orderTransportEditText.setText(orderTransport);
        orderInvoicePerEditText.setText(orderInvoicePer);
        orderChargeEditText.setText(orderCharge);
        orderGoodsDispatchEditText.setText(orderGoodsDispatch);
        orderOthersEditText.setText(orderOthers);
        if(orderIsDirect == 0)
            orderIsDirectCheckBox.setChecked(false);
        else
            orderIsDirectCheckBox.setChecked(true);
    }
}

愿此代码对您有帮助...

谢谢...

于 2013-05-16T07:03:05.727 回答
1

我不太确定这个问题是否仍然困扰着你，因为它已经有几个月了。但我想分享一下我是如何处理这个问题的。这是源代码：

int FLAG = 0;
private View rootView;
private LinearLayout parentView;

/**
 * The fragment argument representing the section number for this fragment.
 */
private static final String ARG_SECTION_NUMBER = "section_number";

/**
 * Returns a new instance of this fragment for the given section number.
 */
public static Fragment2 newInstance(Bundle bundle) {
    Fragment2 fragment = new Fragment2();
    Bundle args = bundle;
    fragment.setArguments(args);
    return fragment;
}

public Fragment2() {

}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    super.onCreateView(inflater, container, savedInstanceState);
    Log.e("onCreateView","onCreateView");
    if(FLAG!=12321){
        rootView = inflater.inflate(R.layout.fragment_create_new_album, container, false);
        changeFLAG(12321);
    }       
    parentView=new LinearLayout(getActivity());
    parentView.addView(rootView);

    return parentView;
}

/* (non-Javadoc)
 * @see android.support.v4.app.Fragment#onDestroy()
 */
@Override
public void onDestroy() {
    // TODO Auto-generated method stub
    super.onDestroy();
    Log.e("onDestroy","onDestroy");
}

/* (non-Javadoc)
 * @see android.support.v4.app.Fragment#onStart()
 */
@Override
public void onStart() {
    // TODO Auto-generated method stub
    super.onStart();
    Log.e("onstart","onstart");
}

/* (non-Javadoc)
 * @see android.support.v4.app.Fragment#onStop()
 */
@Override
public void onStop() {
    // TODO Auto-generated method stub
    super.onStop();
    if(false){
        Bundle savedInstance=getArguments();
        LinearLayout viewParent;

        viewParent= (LinearLayout) rootView.getParent();
        viewParent.removeView(rootView);

    }
    parentView.removeView(rootView);

    Log.e("onStop","onstop");
}
@Override
public void onPause() {
    super.onPause();
    Log.e("onpause","onpause");
}

@Override
public void onResume() {
    super.onResume();
    Log.e("onResume","onResume");
}

这是 MainActivity：

/**
 * Fragment managing the behaviors, interactions and presentation of the
 * navigation drawer.
 */
private NavigationDrawerFragment mNavigationDrawerFragment;

/**
 * Used to store the last screen title. For use in
 * {@link #restoreActionBar()}.
 */

public static boolean fragment2InstanceExists=false;
public static Fragment2 fragment2=null;

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

    mNavigationDrawerFragment = (NavigationDrawerFragment) getSupportFragmentManager()
            .findFragmentById(R.id.navigation_drawer);
    mTitle = getTitle();

    // Set up the drawer.
    mNavigationDrawerFragment.setUp(R.id.navigation_drawer,
            (DrawerLayout) findViewById(R.id.drawer_layout));
}

@Override
public void onNavigationDrawerItemSelected(int position) {
    // update the main content by replacing fragments
    FragmentManager fragmentManager = getSupportFragmentManager();
    FragmentTransaction fragmentTransaction=fragmentManager.beginTransaction();
    switch(position){
    case 0:
        fragmentTransaction.addToBackStack(null);
        fragmentTransaction.replace(R.id.container, Fragment1.newInstance(position+1)).commit();
        break;
    case 1:

        Bundle bundle=new Bundle();
        bundle.putInt("source_of_create",CommonMethods.CREATE_FROM_ACTIVITY);

        if(!fragment2InstanceExists){
            fragment2=Fragment2.newInstance(bundle);
            fragment2InstanceExists=true;
        }
        fragmentTransaction.addToBackStack(null);
        fragmentTransaction.replace(R.id.container, fragment2).commit();

        break;
    case 2:
        fragmentTransaction.addToBackStack(null);
        fragmentTransaction.replace(R.id.container, FolderExplorerFragment.newInstance(position+1)).commit();
        break;
    default: 
        break;
    }
}

parentView 是关键点。通常，在onCreateView时，我们只使用return rootView。但是现在，我将rootView添加到parentView，然后返回parentView。为防止出现“The specified child has a parent. You must call removeView() on the ...”错误，我们需要调用“parentView.removeView(rootView)”，否则我提供的方法没用。我也想分享我是如何找到它的。首先，我设置了一个布尔值来指示实例是否存在。当实例存在时，rootView 不会再次膨胀。但是后来，logcat给了child已经有了parent的东西，所以我决定用另一个parent作为中间的Parent View。这就是它的工作原理。希望对你有帮助。

于 2014-10-17T03:12:15.530 回答
0

让我写下我处理这个问题的方法。我在 Activity 中保留了一个片段对象变量，以供以后交互。在 onCreate() 方法中，我检查是否存在 savedInstanceState （由屏幕旋转或其他原因引起）。

public class MainActivity extends AppCompatActivity {
PlaceAddFragment mFragment;

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

    if(savedInstanceState == null) {
        mFragment = new PlaceAddFragment();
        mFragment.setProfileImages(incomingPics);

        getSupportFragmentManager()
                .beginTransaction()
                .replace(R.id.form_fragment_holder, mFragment, PlaceAddFragment.TAG)
                .commit();
    }else{
        mFragment = (PlaceAddFragment) getSupportFragmentManager().findFragmentByTag(PlaceAddFragment.TAG);
    }
}

在我的片段类中，我重写了 onSaveInstanceState 方法，并在其中添加了 setRetainInstance(true)，如下所示：

public class PlaceAddFragment extends Fragment {
public static final String TAG = ".PlaceAddFragment";
private ProfileImageAdapter mAdapter;
private List<ProfileImage> mProfileImages;
private Context mContext;

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

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {

    mContext = getContext();
    View view = inflater.inflate(R.layout.fragment_place_add, container, false);

    RecyclerView mRecyclerView = (RecyclerView) view.findViewById(R.id.hw_pictures_holder);
    mRecyclerView.setLayoutManager(new LinearLayoutManager(mContext, LinearLayoutManager.HORIZONTAL, false));
    mAdapter = new ProfileImageAdapter(mContext, mProfileImages);
    mRecyclerView.setAdapter(mAdapter);

    return view;
}

@Override
public void onSaveInstanceState(final Bundle outState) {
    super.onSaveInstanceState(outState);
    setRetainInstance(true);
}

@Override
public void onDestroy() {
    super.onDestroy();
    mAdapter = null;
    mProfileImages = null;
}

public void setProfileImages(List<ProfileImage> incomingPics) {
    this.mProfileImages = incomingPics;
}

public List<ProfileImage> getProfileImages() {
    return this.mProfileImages;
}
}

如果您希望此代码正常工作，您应该实现 ProfileImageAdapter mAdapter、ProfileImage 对象和所有这些的 xml 布局。

于 2016-09-20T11:59:15.930 回答