Calling NotifyAll to Update RecyclerView from External Method

Question

I have a RecyclerView (with an Adapter, ViewHolder, etc.), and I need to update the data (the IEnumerable passed to the Adapter). In order for this to be updated in the RecyclerView, I need to call NotifyAll(). However, this gives me the following message:

Java.Lang.IllegalMonitorStateException: 'object not locked by thread before notify()'

I have seen stuff about Java requiring synchronized locks & other stuff for this. I am not familiar with Java, and I am using C# for this Xamarin.Android app. This is my first Xamarin.Android app, so I am new to RecyclerView and Android. Can anybody help my figure out how to update my RecyclerView from an external method? Thanks.

Answer 1

Hello,

Welcome to our Microsoft Q&A platform!

You can add a function in the Adapter of your RecyclerView(e.g. UpDateData) and call NotifyDataSetChanged in your Adapter .

public void UpDateData(List<Photo> addedPhotos) {  

mPhotoAlbum.AddRange(addedPhotos);  
NotifyDataSetChanged();  
 }  

You can refer to the full code of amy demo:
1.my adapter PhotoAlbumAdapter:

public class PhotoAlbumAdapter: RecyclerView.Adapter  
{  
    public event EventHandler<int> ItemClick;  
    public static List<Photo> mPhotoAlbum = new List<Photo>();  

    public static RecyclerView.Adapter adapter;  

    public PhotoAlbumAdapter(List<Photo> branchesList)  
    {  
        adapter = this;  
        mPhotoAlbum = branchesList;  
    }  
  //  add function `UpDateData` here and call `NotifyDataSetChanged`  
    public void UpDateData(List<Photo> addedPhotos) {  

        mPhotoAlbum.AddRange(addedPhotos);  
        NotifyDataSetChanged();  
    }  

    public override RecyclerView.ViewHolder OnCreateViewHolder(ViewGroup parent, int viewType)  
    {  
        View itemView = LayoutInflater.From(parent.Context).Inflate(Resource.Layout.PhotoCardView, parent, false);  

        PhotoViewHolder vh = new PhotoViewHolder(itemView, OnClick);  

        return vh;  
    }  

    public override void OnBindViewHolder(RecyclerView.ViewHolder holder, int position)  
    {  
        PhotoViewHolder vh = holder as PhotoViewHolder;  
        //***********************  
        Photo item=   mPhotoAlbum[position];  

        vh.Caption.Text = item.Caption;  

        vh.MyCheckBox.SetOnCheckedChangeListener(null);  
        vh.MyCheckBox.SetOnCheckedChangeListener(new MyListener(item));  
        vh.MyCheckBox.Checked = item.isChecked;  

        vh.DeleteButton.SetOnClickListener(new MyRemoveItem(item,position));  

    }  


    class MyRemoveItem : Java.Lang.Object, View.IOnClickListener  
    {  
        Photo photo;  
        int position;  
        public MyRemoveItem(Photo item,int position) {  
            this.photo = item;  
            this.position = position;  
        }  

        public void OnClick(View v)  
        {  
            mPhotoAlbum.Remove(photo);  

            adapter.NotifyDataSetChanged();  
        }  
    }  



    class MyListener : Java.Lang.Object, CompoundButton.IOnCheckedChangeListener  
    {  
        Photo photo;  

        public MyListener( Photo item)  
        {  
            this.photo = item;  
        }  

        public void OnCheckedChanged(CompoundButton buttonView, bool isChecked)  
        {  
            photo.isChecked = isChecked;  
        }  
    }  

    public override int ItemCount  
    {  
        get { return mPhotoAlbum.Count; }  
    }  

    // Raise an event when the item-click takes place:  
    void OnClick(int position)  
    {  
        if (ItemClick != null)  
            ItemClick(this, position);  
    }  
}  

2.when we click a button ,we can add some new data to the exsited list:

          refreshBtn = FindViewById<Button>(Resource.Id.refreshBtn);  
        refreshBtn.Click += delegate  
        {  
            List<Photo> photos = new List<Photo>();  
            photos.Add(new Photo{mPhotoID = Resource.Drawable.before_mobile_phones,mCaption = "Before mobile phones",isChecked=false });  
            photos.Add(new Photo {mPhotoID = Resource.Drawable.eurostar,mCaption = "Eurostar Train",isChecked=false });  
            mAdapter.UpDateData(photos);  
         };  

Update:

You can also try to put your code into the RunOnUiThread and change this.NotifyAll(); to NotifyDataSetChanged(); ,you can refer to the following code:

        refreshBtn.Click += delegate  
        {  
            Task.Run(() =>  
            {  
                // Perform a task  
                RunOnUiThread(() =>  
                {  
                   // manipulate UI controls  
                   ((PhotoAlbumAdapter)this.mRecyclerView.GetAdapter()).ResetValues();  
                });  
            });  
        };  

And in your Adapter

    public void ResetValues()  
    {  
        mPhotoAlbum.ForEach((td) => { td.mCaption = "updated data"; });  
        //this.NotifyAll();  
        NotifyDataSetChanged();  
    }  

Best Regards,

Jessie Zhang

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