how to implement OnClickListener for custom ViewHo

问题:

i am creating an app that is supposed to display bluetooth devices in a recyclerview and i want a user to be able to click the items to perform an action. for now i am just attempting to make a toast appear on click but later i would like to possibly display a dialog giving choices to pair, etc. however i am apperently missing something in my usage of onclicklistener. i am attempting to have my ViewHolder class: DeviceHolder implement View.OnClickListener and placing the call to Toast.makeText() inside of my onClick override. however, nothing is happening. i am sure i am just missing something minor and would appreciate help finding the problem. also i am doing this in kotlin which i am new to and if there is possibly a more efficient, kotlin type of way to do this that would also be of help. i am posting my code below. thanks in advance.

class DeviceAdapter(val mContext : Context) : RecyclerView.Adapter<DeviceAdapter.DeviceHolder>(){

val mDevices = ArrayList<BluetoothDevice>()

interface OnClickListener{
    fun onClick(v: View)
}

fun updateItems(list: ArrayList<BluetoothDevice>){
    mDevices.clear()
    mDevices.addAll(list)
    Log.d(TAG, "updating items : $mDevices")
    notifyDataSetChanged()
}

fun ViewGroup.inflate(@LayoutRes res: Int, attachToRoot: Boolean = false): View{
    return LayoutInflater.from(mContext).inflate(res, this, attachToRoot)
}

override fun onBindViewHolder(holder: DeviceHolder, position: Int) {
    Log.d(TAG, "onBindViewHolder called!")
    holder.bindItems(mDevices.get(position))
}

override fun onCreateViewHolder(parent: ViewGroup?, viewType: Int): DeviceAdapter.DeviceHolder{
    Log.d(TAG, "onCreateViewHolder called!")
    val v = parent!!.inflate(R.layout.device_item, false)
    return DeviceHolder(v)
}

override fun getItemCount(): Int {
    return mDevices.size
}

inner class DeviceHolder(itemView: View) : RecyclerView.ViewHolder(itemView), View.OnClickListener {

    override fun onClick(v: View?) {
        Toast.makeText(mContext, "test", Toast.LENGTH_LONG).show()
    }

    val nameView = itemView.findViewById(R.id.nameView) as TextView
    val addrView = itemView.findViewById(R.id.addressView) as TextView

    fun bindItems(btDevice: BluetoothDevice) {
        Log.d(TAG, "holder created!")
        nameView.text = btDevice.name
        addrView.text = btDevice.address
        itemView.setOnClickListener { this }
    }

}

companion object {
    val TAG = "Device Adapter"
}
}

here are the log messages:

10-09 00:35:50.233 7581-7581/com.example.zemcd.toofxchange D/DiscoveryTask: device found!
10-09 00:35:51.795 7581-7581/com.example.zemcd.toofxchange D/DiscoveryTask: device found!
10-09 00:35:56.752 7581-7581/com.example.zemcd.toofxchange D/DiscoveryTask: device list : [**:B8:9A:39:1D:**, **:DF:BF:2A:F3:**]
10-09 00:35:56.752 7581-7581/com.example.zemcd.toofxchange D/Device Adapter: updating items : [**:B8:9A:39:1D:**, **:DF:BF:2A:F3:**]
10-09 00:35:56.752 7581-7581/com.example.zemcd.toofxchange D/DiscoveryTask: discovery finished
10-09 00:35:56.762 7581-7581/com.example.zemcd.toofxchange D/Device Adapter: onCreateViewHolder called!
10-09 00:35:56.774 7581-7581/com.example.zemcd.toofxchange D/Device Adapter: onBindViewHolder called!
10-09 00:35:56.774 7581-7581/com.example.zemcd.toofxchange D/Device Adapter: holder created!
10-09 00:35:56.783 7581-7581/com.example.zemcd.toofxchange D/Device Adapter: onCreateViewHolder called!
10-09 00:35:56.786 7581-7581/com.example.zemcd.toofxchange D/Device Adapter: onBindViewHolder called!
10-09 00:35:56.786 7581-7581/com.example.zemcd.toofxchange D/Device Adapter: holder created!

回答1:

i managed to get this fixed by eliminating the implementation of OnClickListener and just using this statement instead itemView.setOnClickListener { /* lamda here */ }. i don't believe this exact syntax is available in java but in kotlin in works. here is my revised code :

inner class DeviceHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {

    val nameView = itemView.findViewById(R.id.nameView) as TextView
    val addrView = itemView.findViewById(R.id.addressView) as TextView

    fun bindItems(btDevice: BluetoothDevice) {
        Log.d(TAG, "holder created!")
        nameView.text = btDevice.name
        addrView.text = btDevice.address
        itemView.setOnClickListener { Toast.makeText(it.context, "testing", Toast.LENGTH_SHORT).show() }
    }

}

by using the it keyword inside of the lambda i accessed the context of the itemView object, instead of using my original mContext described above. i am still unsure of exactly why my old approach did not work, but this did so that works for me.

回答2:

This works:

1 set your own click listener to the adapter, and keep a reference to it:

private OnItemClickListener onItemClickListener;
// ...
public interface OnItemClickListener {
    // note: here you would need some params, for instance the view
    void onItemClick(View v);
}

public void setOnItemClickListener(OnItemClickListener l) {
    this.onItemClickListener = l;
}

2 when each viewholder is created, set a listener to it, and once called back, pass the callback to the listener set in 1:

@Override
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    ViewHolder vh = getViewHolder( /*...*/ );
    vh.setOnItemClickListener(new OnItemClickListener() {                
        if (onItemClickListener != null) {
            // each view holder calls the one listener set to the Adapter
            onItemClickListener.onItemClick(v);
        }
    }
}

3 make your viewholder to listen to the (holded) view onClick, and let it forward the call:

public static class ViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {
// each view holder has a listener set to it   
private OnItemClickListener mListener;

public ViewHolder(View v) {        
    super(v);
    // ...
    // set the viewholder as a listener to the view's clicks
    v.setOnClickListener(this);
}

@Override
public void onClick(View v) {
    // when view is clicked, simply forward the call
    if (mListener != null) {
        mListener.onItemClick(v);
    }
}

public void setOnItemClickListener(OnItemClickListener listener) {
    mListener = listener;
}

}

4 at this point, the adapter user will have:

mAdapter = new MyAdapter(ctx);
mAdapter.setOnItemClickListener(new MyAdapter.OnItemClickListener() {
    @Override
    public void onItemClick(View v) {
        // the given view was clicked, do something with it
    }
});

回答3:

According to your code you are implementing the clicklistner but haven't added any register to click listener.add the clickListener for nameView and AddrView.

nameView.setOnClickListener(this);
addrView.setOnClickListener(this);