android java/kotlin recyclerview 项目不可见

Question

我正在尝试构建一个扫描蓝牙设备并将它们显示在回收站视图中的应用程序。 我正在使用 java 编写一些应用程序，而在 kotlin 中编写一些应用程序。 出于某种原因，我的 recyclerview 项目不可见。 有人请帮我找出我犯了什么错误。 我正在发布我的活动代码以及我的回收站视图。 澄清我的问题。 发现成功，找到设备，我的适配器中所有继承的方法好像都被调用了。 我在其中放置了日志消息，但在 recyclerview 中仍然看不到任何内容。 为什么什么都不显示？ 这是我用 java 编写的活动：

public class ToofActivity extends AppCompatActivity implements CompoundButton.OnCheckedChangeListener {

private static final String TAG = "ToofActivity";
private static final int REQUEST_COARSE_LOCATION = 222;

private static BluetoothAdapter btAdapter;

private TextView mStatusLabel;
private Switch mStatusSwitch;
private ProgressBar mProgressBar;
private RecyclerView mDeviceRecylcer;
private static ArrayList<BluetoothDevice> mDevices = new ArrayList<>();
private DeviceAdapter mAdapter;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_toof);

    checkLocationPermission();

    btAdapter = BluetoothAdapter.getDefaultAdapter();

    mStatusLabel = (TextView) findViewById(R.id.status_view);
    mStatusLabel.setText(btAdapter.isEnabled() ? "Active" : "Inactive");
    mStatusSwitch = (Switch) findViewById(R.id.status_switch);
    mStatusSwitch.setChecked(btAdapter.isEnabled());
    mStatusSwitch.setOnCheckedChangeListener(this);
    mProgressBar = (ProgressBar) findViewById(R.id.search_progress_bar);
    mDeviceRecylcer = (RecyclerView) findViewById(R.id.device_recycler);

    mDeviceRecylcer.setLayoutManager(new LinearLayoutManager(this));
    mAdapter = new DeviceAdapter(getApplicationContext());
    mDeviceRecylcer.setAdapter(mAdapter);

}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    MenuInflater inflater = getMenuInflater();
    inflater.inflate(R.menu.options_menu, menu);
    return super.onCreateOptionsMenu(menu);
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    switch (item.getItemId()) {
        case R.id.searchOption:
            DiscoveryTask discovery = new DiscoveryTask(btAdapter, this, mProgressBar);
            discovery.setOnCompleteListener(new DiscoveryTask.OnCompletedListener() {
                @Override
                public void onComplete() {
                    mAdapter.updateItems(mDevices);
                }
            });
            discovery.execute((Void) null);
            break;
    }

    return true;
}

@Override
public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
    if (isChecked) {
        btAdapter.enable();
        mStatusLabel.setText("Active");
    } else {
        btAdapter.disable();
        mStatusLabel.setText("Inactive");
    }
}

public static void setDeviceList(ArrayList<BluetoothDevice> deviceList) {
    mDevices.clear();
    mDevices = deviceList;
}

protected void checkLocationPermission() {
    if (this.checkSelfPermission(Manifest.permission.ACCESS_COARSE_LOCATION)
            != PackageManager.PERMISSION_GRANTED) {

        ActivityCompat.requestPermissions(this,
                new String[]{Manifest.permission.ACCESS_COARSE_LOCATION},
                REQUEST_COARSE_LOCATION);
    }
}

@Override
public void onRequestPermissionsResult(int requestCode,
                                       String permissions[], int[] grantResults) {
    switch (requestCode) {
        case REQUEST_COARSE_LOCATION: {
            if (grantResults.length <= 0
                    || grantResults[0] != PackageManager.PERMISSION_GRANTED) {
                checkLocationPermission();
                break;
            }
        }
    }
}
}

这是我用 kotlin 编写的 recyclerview 的代码：

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

val mDevices = ArrayList<BluetoothDevice>()

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

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

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

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

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
    }
}

companion object {
    val TAG = "DeviceAdapter"
}

}

谢谢你帮助我。

Answer 1

您可以删除承包商适配器中的上下文，并可以使用适配器val v = LayoutInflater.from(mContext).inflate(R.layout.device_item, parent, false)上下文替换此行到val v = LayoutInflater.from(parent.context).inflate(R.layout.device_item, parent, false)或者如果您希望适配器内的上下文作为参数，请替换此语句

 mAdapter = new DeviceAdapter(getApplicationContext());

to mAdapter = new DeviceAdapter(this);

Answer 2

这里的问题是我使用的上下文。 我的上下文是从getApplicationContext()返回的不正确的上下文。 现在我已将其更改为仅使用this 。 进行更改后，所有视图项都可见。