如何在Android中使用Firebase實現自定義PagerAdapter？

我試圖實現一個自定義的PagerAdapter實現Firebase，就像FirebaseListAdapter和FirebaseRecyclerAdapter一樣。我查看了GitHub here上的源代碼，但在Android Studio中遇到了一些錯誤。下面是一個使用了大量的類都是從給定鏈路我FirebasePagerAdapter：如何在Android中使用Firebase實現自定義PagerAdapter？

ChangeEventListener
ClassSnapshotParser
FirebaseAdapter
FirebaseArray

ObservableSnapshotArray：從給定鏈路使用

public abstract class FirebasePagerAdapter<T> extends PagerAdapter implements FirebaseAdapter, ChangeEventListener { 

    private static String TAG = "firebasepageradapter"; 
    protected final Activity mActivity; 
    protected final ObservableSnapshotArray<T> mSnapshots; 
    protected final int mLayout; 

    /** 
    * @param activity The {@link Activity} containing the {@link android.support.v4.view.ViewPager} 
    * @param modelLayout This is the layout used to represent a single list item. You will be 
    *     responsible for populating an instance of the corresponding view with the 
    *     data from an instance of modelClass. 
    * @param snapshots The data used to populate the adapter 
    */ 
    public FirebasePagerAdapter(Activity activity, 
           ObservableSnapshotArray<T> snapshots, 
           @LayoutRes int modelLayout) { 
     mActivity = activity; 
     mSnapshots = snapshots; 
     mLayout = modelLayout; 

     startListening(); 
    } 

    /** 
    * @param parser a custom {@link SnapshotParser} to convert a {@link DataSnapshot} to the model 
    *    class 
    * @param query The Firebase location to watch for data changes. Can also be a slice of a 
    *    location, using some combination of {@code limit()}, {@code startAt()}, and 
    *    {@code endAt()}. <b>Note, this can also be a {@link DatabaseReference}.</b> 
    * @see #FirebasePagerAdapter(Activity, ObservableSnapshotArray, int) 
    */ 
    public FirebasePagerAdapter(Activity activity, 
           SnapshotParser<T> parser, 
           @LayoutRes int modelLayout, 
           Query query) { 
     this(activity, new FirebaseArray<>(query, parser), modelLayout); 
    } 

    /** 
    * @see #FirebasePagerAdapter(Activity, SnapshotParser, int, Query) 
    */ 
    public FirebasePagerAdapter(Activity activity, 
           Class<T> modelClass, 
           @LayoutRes int modelLayout, 
           Query query) { 
     this(activity, new ClassSnapshotParser<>(modelClass), modelLayout, query); 
    } 

    @Override 
    public int getCount() { 
     return mSnapshots.size(); 
    } 

    @Override 
    public boolean isViewFromObject(View view, Object object) { 
     return false; 
    } 

    @Override 
    public void startListening() { 
     if (!mSnapshots.isListening(this)) { 
      mSnapshots.addChangeEventListener(this); 
     } 
    } 

    @Override 
    public void cleanup() { 
     mSnapshots.removeChangeEventListener(this); 
    } 

    @Override 
    public Object getItem(int position) { 
     return mSnapshots.get(position).getKey().hashCode(); 
    } 

    @Override 
    public DatabaseReference getRef(int position) { 
     return mSnapshots.get(position).getRef(); 
    } 

    @Override 
    public void onChildChanged(ChangeEventListener.EventType type, DataSnapshot snapshot, int index, int oldIndex) { 
     notifyDataSetChanged(); 
    } 

    @Override 
    public void onDataChanged() { 

    } 

    @Override 
    public void onCancelled(DatabaseError error) { 
     Log.w(TAG, error.toException()); 
    } 

    @Override 
    public Object instantiateItem(ViewGroup container, int position) { 
     View view = mActivity.getLayoutInflater().inflate(mLayout, container, false); 

     T model = getItem(position); 

     // Call out to subclass to marshall this model into the provided view 
     populateView(view, model, position); 

     return view; 
    } 

    /** 
    * Each time the data at the given Firebase location changes, 
    * this method will be called for each item that needs to be displayed. 
    * The first two arguments correspond to the mLayout and mModelClass given to the constructor of 
    * this class. The third argument is the item's position in the list. 
    * <p> 
    * Your implementation should populate the view using the data contained in the model. 
    * 
    * @param v  The view to populate 
    * @param model The object containing the data used to populate the view 
    * @param position The position in the list of the view being populated 
    */ 
    protected abstract void populateView(View v, T model, int position); 

}

類

前提
SnapshotParser

我已經強烈搜查谷歌和SO爲例或解決方案，但儘管需要一個FirebasePagerAdapter，沒有人提出了一個解決方案，或者至少使其公開。我希望得到此工作並將其公開給其他可能會發現它有用的開發人員。

我得到的錯誤是在instantiateItem方法T model = getItem(position);「不兼容的類型：需要T，發現物體」與this(activity, new FirebaseArray<>(query, parser), modelLayout);「不能推斷論據」。

我的希望是通過解決這些錯誤，適配器將按預期工作。

來源

2017-07-07 Steve C.

注意：這不是其他類似問題的重複。我看過其他的SO問題，他們都沒有給出他們嘗試過的或者從頭開始的例子。這個問題爲任何能夠幫助解決問題的人提供了一個很好的起點。 –

我已經通過將getItem方法更改爲GenericType public T getItem(int position)來解決此問題。它現在完美。這裏是我的完整FirebasePagerAdapter類：

public abstract class FirebasePagerAdapter<T> extends PagerAdapter implements FirebaseAdapter, ChangeEventListener { 

    private static String TAG = "firebasepageradapter"; 
    protected final Activity mActivity; 
    protected final ObservableSnapshotArray<T> mSnapshots; 
    protected final int mLayout; 

    /** 
    * @param activity The {@link Activity} containing the {@link android.support.v4.view.ViewPager} 
    * @param modelLayout This is the layout used to represent a single list item. You will be 
    *     responsible for populating an instance of the corresponding view with the 
    *     data from an instance of modelClass. 
    * @param snapshots The data used to populate the adapter 
    */ 
    public FirebasePagerAdapter(Activity activity, 
           ObservableSnapshotArray<T> snapshots, 
           @LayoutRes int modelLayout) { 
     mActivity = activity; 
     mSnapshots = snapshots; 
     mLayout = modelLayout; 

     startListening(); 
    } 

    /** 
    * @param parser a custom {@link SnapshotParser} to convert a {@link DataSnapshot} to the model 
    *    class 
    * @param query The Firebase location to watch for data changes. Can also be a slice of a 
    *    location, using some combination of {@code limit()}, {@code startAt()}, and 
    *    {@code endAt()}. <b>Note, this can also be a {@link DatabaseReference}.</b> 
    * @see #FirebasePagerAdapter(Activity, ObservableSnapshotArray, int) 
    */ 
    public FirebasePagerAdapter(Activity activity, 
           SnapshotParser<T> parser, 
           @LayoutRes int modelLayout, 
           Query query) { 
     this(activity, new FirebaseArray<>(query, parser), modelLayout); 
    } 

    /** 
    * @see #FirebasePagerAdapter(Activity, SnapshotParser, int, Query) 
    */ 
    public FirebasePagerAdapter(Activity activity, 
           Class<T> modelClass, 
           @LayoutRes int modelLayout, 
           Query query) { 
     this(activity, new ClassSnapshotParser<>(modelClass), modelLayout, query); 
    } 

    @Override 
    public int getCount() { 
     return mSnapshots.size(); 
    } 

    @Override 
    public boolean isViewFromObject(View view, Object object) { 
     return view == object; 
    } 

    @Override 
    public void startListening() { 
     if (!mSnapshots.isListening(this)) { 
      mSnapshots.addChangeEventListener(this); 
     } 
    } 

    @Override 
    public void cleanup() { 
     mSnapshots.removeChangeEventListener(this); 
    } 

    @Override 
    public T getItem(int position) { 
     return mSnapshots.getObject(position); 
    } 

    @Override 
    public DatabaseReference getRef(int position) { 
     return mSnapshots.get(position).getRef(); 
    } 

    @Override 
    public void onChildChanged(ChangeEventListener.EventType type, DataSnapshot snapshot, int index, int oldIndex) { 
     notifyDataSetChanged(); 
    } 

    @Override 
    public void onDataChanged() { 

    } 

    @Override 
    public void onCancelled(DatabaseError error) { 
     Log.w(TAG, error.toException()); 
    } 

    @Override 
    public Object instantiateItem(ViewGroup container, int position) { 
     View view = mActivity.getLayoutInflater().inflate(mLayout, container, false); 

     //T model = getItem(position); 
     T model = getItem(position); 

     // Call out to subclass to marshall this model into the provided view 
     populateView(view, model, position); 
     container.addView(view); 
     return view; 
    } 

    /** 
    * Each time the data at the given Firebase location changes, 
    * this method will be called for each item that needs to be displayed. 
    * The first two arguments correspond to the mLayout and mModelClass given to the constructor of 
    * this class. The third argument is the item's position in the list. 
    * <p> 
    * Your implementation should populate the view using the data contained in the model. 
    * 
    * @param v  The view to populate 
    * @param model The object containing the data used to populate the view 
    * @param position The position in the list of the view being populated 
    */ 
    protected abstract void populateView(View v, T model, int position); 

    @Override 
    public void destroyItem(ViewGroup container, int position, Object object) { 
     container.removeView((RelativeLayout)object); 
    } 

}

我已經發布需要這個一切都在GitHub上工作的其他人可能會發現它很有用。你可以找到它here

來源

2017-07-09 21:03:27

如何在Android中使用Firebase實現自定義PagerAdapter？

回答

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