保存状态自定义RecyclerView

Question

为了在应用程序的列表中启用分页，我创建了一个自定义的RecyclerView。我在恢复状态时崩溃了。也许这个崩溃与支持库中已知的错误有关，但是，从理论上讲，它已经在支持库版本24.0.0: https://code.google.com/p/android/issues/detail?id=196430中得到解决，但它仍然崩溃。

也许我做错了什么?我有一个BadParcelableException ClassNotFoundException when unmarshalling: android.support.v7.widget.RecyclerView$SavedStateHere试图重新创建SavedState。

这是我的SavedState类在CustomRecyclerView控制器:

public static class SavedState extends RecyclerView.BaseSavedState {
    public boolean isLastPage;
    public boolean isLoading;
    public int maxPages;
    public int pageSize;
    public int currentPage;
    public int firstVisibleItem;
    public Parcelable layoutManagerState;
    public SavedState(Parcelable superState) {
        super(superState);
    }
    public SavedState(Parcel source) {
        super(source);
        this.isLastPage = source.readByte() == 1;
        this.isLoading = source.readByte() == 1;
        this.maxPages = source.readInt();
        this.pageSize = source.readInt();
        this.currentPage = source.readInt();
        this.firstVisibleItem = source.readInt();
        this.layoutManagerState = source.readParcelable(LinearLayoutManager.SavedState.class.getClassLoader());
    }
    @Override
    public void writeToParcel(Parcel dest, int flags) {
        super.writeToParcel(dest, flags);
        dest.writeByte((byte) (isLastPage ? 1 : 0));
        dest.writeByte((byte) (isLoading ? 1 : 0));
        dest.writeInt(maxPages);
        dest.writeInt(pageSize);
        dest.writeInt(currentPage);
        dest.writeInt(firstVisibleItem);
        dest.writeParcelable(layoutManagerState, flags);
    }
    public static final Creator<SavedState> CREATOR = new Creator<SavedState>() {
        @Override
        public SavedState createFromParcel(Parcel source) {
            return new SavedState(source);
        }
        @Override
        public SavedState[] newArray(int size) {
            return new SavedState[size];
        }
    };
}

这里是我在控制器中保存和恢复状态的地方:

public Parcelable saveState(Parcelable superState) {
    SavedState savedState       = new SavedState(superState);
    savedState.isLastPage       = this.isLastPage;
    savedState.isLoading        = this.isLoading;
    savedState.maxPages         = this.maxPages;
    savedState.pageSize         = this.pageSize;
    savedState.currentPage      = this.currentPage;
    savedState.firstVisibleItem = this.firstVisibleItemPosition;
    if (layoutManager != null) {
        savedState.layoutManagerState = layoutManager.onSaveInstanceState();
    }
    return savedState;
}
public Parcelable restoreState(SavedState savedState) {
    this.isLastPage                 = savedState.isLastPage;
    this.isLoading                  = savedState.isLoading;
    this.maxPages                   = savedState.maxPages;
    this.pageSize                   = savedState.pageSize;
    this.currentPage                = savedState.currentPage;
    this.firstVisibleItemPosition   = savedState.firstVisibleItem;
    return savedState.layoutManagerState;
}

以下是onSaveInstanceState和onRestoreInstanceState在自定义RecyclerView中的实现:

    @Override
    protected Parcelable onSaveInstanceState() {
        return controller.saveState(super.onSaveInstanceState());
    }
    @Override
    protected void onRestoreInstanceState(Parcelable state) {
        if (state instanceof EndlessRecyclerViewController.SavedState) {
            EndlessRecyclerViewController.SavedState savedState = (EndlessRecyclerViewController.SavedState) state;
            Parcelable layoutManagerState = controller.restoreState(savedState);
            getLayoutManager().onRestoreInstanceState(layoutManagerState);
            super.onRestoreInstanceState(savedState.getSuperState());
        }
        else
            super.onRestoreInstanceState(state);
    }

我也试图从支持AbsSavedState扩展SavedState，但仍然崩溃。我不确定我是否必须调用LinearLayoutManager的onSaveInstanceState…

谢谢!

Answer 1

最后，我从支持库版本24.2.1中使用AbsSavedState(因此，我从它扩展了SavedState类)解决了问题。并从

更改接收Parcel对象的constructor:

public SavedState(Parcel source) {
  super(source);
  //... 
}

:

public SavedState(Parcel source) {
  super(source, LinearLayoutManager.class.getClassLoader());
  //... 
}

Answer 2

当我第一次尝试你的解决方案时，我很高兴，因为它实际上有效。然而，当我查看其他Android代码时，我发现了一个更好的解决方案。您需要添加一个新的构造函数，并从创建器调用它。

// add new constructor
@RequiresApi(Build.VERSION_CODES.N)
public SavedState(Parcel source, ClassLoader loader) {
    super(source, loader);
    this.isLastPage = source.readByte() == 1;
    this.isLoading = source.readByte() == 1;
    this.maxPages = source.readInt();
    this.pageSize = source.readInt();
    this.currentPage = source.readInt();
    this.firstVisibleItem = source.readInt();
    this.layoutManagerState = source.readParcelable(LinearLayoutManager.SavedState.class.getClassLoader());
}
public static final Creator<SavedState> CREATOR = new ClassLoaderCreator<SavedState>() {
    // add createFromParcel method with ClassLoader
    @Override
    public SavedState createFromParcel(Parcel source, ClassLoader loader)
    {
        return Build.VERSION.SDK_INT >= Build.VERSION_CODES.N ? new SavedState(source, loader) : new SavedState(source);
    }
    @Override
    public SavedState createFromParcel(Parcel source)
    {
        // call other createFromParcel method.    
        return createFromParcel(source, null);
    }
    @Override
    public SavedState[] newArray(int size) {
        return new SavedState[size];
    }
};