可包裹类不构成可包裹对象

Question

I am trying to save an ArrayList of objects (List shelfItems) in the bundle to retrieve it next time the activity is opened.

(the activity gets info from firestore and I want to decrease reads and take away loading time each time the activity is opened).

but i get this error message:

savedInstanceState.putParcelableArrayList("key", shelfItems);

"putParcelableArrayList(java.lang.String, java.util.ArrayList)' in 'android.os.Bundle' cannot be applied to '(java.lang.String, java.util.List)"

This is my object class:

import android.os.Parcel;
import android.os.Parcelable;

public class ShelfItem implements Parcelable{


    private String mTitle;
    private String mAuthor;
    private String mThumbnail;
    private long mRating;
    private long mEndDate;
    private long mBeginDate;
    private String mId;
    private long mPages;
    private boolean mVisible;

    //make ShelfItem object
    public ShelfItem(String title, String author, String thumbnail, long rating, long beginDate, long endDate, String id, long pages, boolean visible) {
        mTitle = title;
        mAuthor = author;
        mThumbnail = thumbnail;
        mRating = rating;
        mBeginDate = beginDate;
        mEndDate = endDate;
        mId = id;
        mPages = pages;
        mVisible = visible;
    }


    public String getTitle() {
        return mTitle;
    }

    public String getAuthor() {
        return mAuthor;
    }

    public String getThumbnail() {
        return mThumbnail;
    }

    public long getRating() {
        return mRating;
    }

    public long getBeginDate() {
        return mBeginDate;
    }

    public long getEndDate() {
        return mEndDate;
    }

    public String getId() {
        return mId;
    }

    public long getPages() {
        return mPages;
    }

    public boolean getVisible() {
        return mVisible;
    }


    public ShelfItem(Parcel in) {
        mId = in.readString();
        mTitle = in.readString();
        mAuthor = in.readString();
        mThumbnail = in.readString();
        mBeginDate = in.readLong();
        mEndDate = in.readLong();
        mPages = in.readLong();
        mVisible = in.readByte() != 0;
        mRating = in.readLong();

    }

    public int describeContents() {
        return 0;
    }

    public void writeToParcel(Parcel out, int flags) {
        out.writeString(mId);
        out.writeString(mTitle);
        out.writeString(mAuthor);
        out.writeString(mThumbnail);
        out.writeLong(mBeginDate);
        out.writeLong(mEndDate);
        out.writeLong(mPages);
        out.writeByte((byte) (mVisible ? 1 : 0));
        out.writeLong(mRating);

    }

    public static final Parcelable.Creator<ShelfItem> CREATOR = new Parcelable.Creator<ShelfItem>() {
        public ShelfItem createFromParcel(Parcel in) {
            return new ShelfItem(in);
        }

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

}

and this is how I try to save the list:

@Override
    public void onSaveInstanceState(Bundle savedInstanceState) {
        super.onSaveInstanceState(savedInstanceState);
        savedInstanceState.putParcelableArrayList("key", shelfItems);
    }

Answer 1

As we learn Java, we're taught to use the interface type ( List ) instead of the implementation type ( ArrayList ) when we declare our variables. You probably have code somewhere that looks like this:

List<ShelfItem> shelfItems = new ArrayList<>();

However, in the particular case of Bundle and saving lists, you must use ArrayList specifically, and not any List in general.

If I'm right, and your list is declared like I've shown above, just change it to explicitly use ArrayList :

ArrayList<ShelfItem> shelfItems = new ArrayList<>();

If you're getting the list from somewhere else, and you can't control the implementation type of it, you can construct a new ArrayList when you need to save it:

@Override
public void onSaveInstanceState(Bundle savedInstanceState) {
    super.onSaveInstanceState(savedInstanceState);
    ArrayList<ShelfItem> toSave = new ArrayList<>(shelfItems);
    savedInstanceState.putParcelableArrayList("key", toSave);
}