使用 Parcelable 在 Fragment 之间传递 ArreyList

Question

在使用 Retrofit 使用 json 并使用异步回调后，我无法将 MainActivity 中的 An ArrayList 传递给片段。

来自 MainActivity 的代码：

 lFragmentManager = getFragmentManager();
            lFragment = lFragmentManager.findFragmentById(R.id.frame_container);
            lFragment = new Fragment_Categories();
            Bundle bundle = new Bundle();
            bundle.putParcelableArrayList("list_categories", Categories_.getCategories());
            //for(int a = 0 ; a < Categories_.getCategories().size(); a++)
            //   Log.d("billy",Categories_.getCategories().get(a).getTitle());
            lFragment.setArguments(bundle);
        lFragmentManager.beginTransaction().replace(R.id.frame_container ,lFragment ).commit();

请注意，cmets 中的 Log 确实会打印列表的上下文，因此我将片段中的 ArrayList 与 onCreateView 中的这段代码一起使用：

if(savedInstanceState != null)
        categories =  savedInstanceState.getParcelableArrayList("list_categories");

    /*
     * initialize the Recycler view
     */
    mRecycler = (RecyclerView)view.findViewById(R.id.categories_list);
    mAdapter = new AdapterCategories(categories,getActivity());
    mRecycler.setAdapter(mAdapter);

这是我的班级类别：

public class Categories implements Parcelable{

private ArrayList<NavDrawerItem> categories;

@Override
public int describeContents() {
    return 0;
}

@Override
public void writeToParcel(Parcel dest, int flags) {
    dest.writeTypedList(categories);

}

public static final Parcelable.Creator<Categories> CREATOR = new Parcelable.Creator<Categories>() {

    public Categories createFromParcel(Parcel in) {
        return new Categories(in);

    }

    public Categories[] newArray(int size){
        return new Categories[size];
    }
};

private Categories(Parcel in){

    categories = in.createTypedArrayList(NavDrawerItem.CREATOR);
}

public ArrayList<NavDrawerItem> getCategories() {
    return categories;
}
}

这里是 NavDrawerItem 类：

public class NavDrawerItem implements Parcelable {

private String title;
private String description;
private String image;
private String post_count;
private String id;
private String slug;
private int parent;

@Override
public int describeContents() {
    return 0;
}

@Override
public void writeToParcel(Parcel dest, int flags) {
    dest.writeString(title);
    dest.writeString(description);
    dest.writeString(image);
    dest.writeString(post_count);
    dest.writeString(id);
    dest.writeString(slug);
    dest.writeInt(parent);
}

public static final Parcelable.Creator<NavDrawerItem> CREATOR = new Parcelable.Creator<NavDrawerItem>() {

    public NavDrawerItem createFromParcel(Parcel in) {
        return new NavDrawerItem(in);

    }

    public NavDrawerItem[] newArray(int size){
        return new NavDrawerItem[size];
    }
};

private NavDrawerItem(Parcel in){
    title = in.readString();
    description = in.readString();
    image = in.readString();
    post_count = in.readString();
    id = in.readString();
    slug = in.readString();
    parent = in.readInt();
}

问题是在片段内部（当试图将列表传递给RecyclerView 的适配器时）或RecyclerView 的适配器内部我接受了一个空异常：

java.lang.NullPointerException：尝试在空对象引用上调用虚拟方法“java.util.ArrayList android.os.Bundle.getParcelableArrayList(java.lang.String)”

谢谢你的帮助！！

Answer 1

您不会使用savedInstanceState 来获取您的参数，因为它们不是作为saveInstanceState() 操作的一部分传递的。您想改用getArguments()。所以试试这个...

categories = getArguments().getParcelableArrayList("list_categories");