Android RecyclerView only displays items after closing and restarting the app

laprof :

I have a strange effect with my RecyclerView after I updated my App to API 28. I have a search button that triggers a search of Wifi devices in my area. The items are no longer displayed directly in the list. I have to close and reopen the app to get the correct display.

I have a toast that should be displayed when the button is pressed. The toast message is also only displayed after closing and opening the app.

Activity.kt

   private fun setFloatingSearchButton() {
        floating_button_discover_devices.setOnClickListener { view ->
            Snackbar.make(view, "Search for new devices ...",
                    Snackbar.LENGTH_SHORT).setAction("Action", null).show()

            discoverDevices()

            registerReceiver(mWifiReceiver, IntentFilter(WifiManager.SCAN_RESULTS_AVAILABLE_ACTION))

            mWifiManager!!.startScan()
        }
    }

WifiAdapter.java

public class WifiAdapter extends RecyclerView.Adapter<WifiAdapter.ViewHolder> {

    private final int CONFIGURE_DEVICE_REQUEST_CODE = 0x00000001;

    private static final String TAG = "WifiAdapter";

    private List<DeviceWifiTo> wifis;

    private Context context;
    private Activity activity;

    public WifiAdapter(List<DeviceWifiTo> wifis) {
        this.wifis = wifis;
    }

    @Override
    public WifiAdapter.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        context = parent.getContext();
        activity = (Activity) context;
        LayoutInflater inflater = LayoutInflater.from(context);

        View wifiView = inflater.inflate(R.layout.item_wifi, parent, false);

        return new WifiAdapter.ViewHolder(wifiView);
    }

    @Override
    public void onBindViewHolder(WifiAdapter.ViewHolder holder, int position) {
        DeviceWifiTo wifi = wifis.get(position);
        Log.d(TAG, wifi.getSsid());
        TextView wifiName = holder.wifiName;
        wifiName.setText(wifi.getSsid());

        CardView cardView = holder.cardView;
        cardView.setOnClickListener(view -> {
            Intent intent = new Intent(context, ConfigureDeviceActivity.class);
            intent.putExtra("ssid", wifi.getSsid());
            activity.startActivityForResult(intent, CONFIGURE_DEVICE_REQUEST_CODE);
        });
    }

    @Override
    public int getItemCount() {
        return wifis.size();
    }

    class ViewHolder extends RecyclerView.ViewHolder {
        TextView wifiName;
        CardView cardView;

        ViewHolder(View itemView) {
            super(itemView);
            wifiName = itemView.findViewById(R.id.text_wifi_name);
            cardView = itemView.findViewById(R.id.cardView_device);
        }
    }

}

UcDiscoverDevicesImpl.java

private void createRecyclerView(List<DeviceWifiTo> list) {
    RecyclerView recyclerView = activity.findViewById(R.id.recycler_view_wifi);
    WifiAdapter adapter = new WifiAdapter(list);
    recyclerView.setAdapter(adapter);
    recyclerView.setLayoutManager(new LinearLayoutManager(activity.getApplicationContext()));
}

Jakir Hossain :

Set layout manager before set adapter to recycler view, Update like below

private void createRecyclerView(List<DeviceWifiTo> list) {
   RecyclerView recyclerView = activity.findViewById(R.id.recycler_view_wifi);
   recyclerView.setLayoutManager(new LinearLayoutManager(activity.getApplicationContext()));
   WifiAdapter adapter = new WifiAdapter(list);
   recyclerView.setAdapter(adapter);

}

Hope it helps you.