Question

我正在为Android构建一个简单的蓝牙应用程序，就像一个小小的学习项目。

我知道通常在android AsyncTask中运行后台线程的正常方法，但我不想使用它。我只是使用Callable和NewFixedThreadPool因为我不像AsyncTask那样熟悉它，我想稍微学习一下。

我正在尝试在后台线程中扫描可发现的设备。在提交可调用之前，我在Activity上显示了一个进度条，在调用方法结束时，我调用了一个回调到主线程，使进度条再次消失，还有一些其他任务。

虽然我的进度条的可见性设置回GONE，但在此之后应该打印出一些日志消息，但它们永远不会打印出来。

此外，我无法拨打unregisterReceiver()。

我的Callable类：

public class ScanTask implements Callable{

private static final String TAG = "ScanTask";

private BluetoothAdapter mAdapter;
private ArrayList<BluetoothDevice> mDevices = new ArrayList<>();
private BroadcastReceiver mBTReceiver = new BTReceiver();
private Context mContext;
private static OnCompletedListener mCompletionListener;

public interface OnCompletedListener{
    void onComplete();
}

public static void setOnCompletedListener(OnCompletedListener listener){
    mCompletionListener = listener;
}

public ScanTask(BluetoothAdapter adapter, Context context, ArrayList<BluetoothDevice> devices){ //constuctor for no future
    mAdapter = adapter;
    mContext = context;
    mDevices = devices;
}

public ScanTask(BluetoothAdapter adapter, Context context){//constructor for future
    mAdapter = adapter;
    mContext = context;
}

public Void call(){//Future will be replace with return type
    IntentFilter filter = new IntentFilter(BluetoothDevice.ACTION_FOUND);
    mContext.registerReceiver(mBTReceiver, filter);
    mAdapter.startDiscovery();

    try {
        Thread.sleep(2000);
    }catch (Exception e){
        e.printStackTrace();
    }

    //callback signals completion
    Log.d(TAG, "before oncomplete " + Thread.currentThread());
    mContext.unregisterReceiver(mBTReceiver);
    Log.d(TAG, "after unRegister");
    mCompletionListener.onComplete();
    Log.d(TAG, "after oncomplete");
    return null;
}

public ArrayList<BluetoothDevice> getDevices(){
    return mDevices;
}

private class BTReceiver extends BroadcastReceiver{

    @Override
    public void onReceive(Context context, Intent intent) {
        String action = intent.getAction();
        switch (action){
            case BluetoothDevice.ACTION_FOUND:
                BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
                mDevices.add(device);
                break;
        }
    }
}
}

以及我的活动中的相关代码：

@Override
public boolean onOptionsItemSelected(MenuItem item){
    switch (item.getItemId()){
        case R.id.searchOption:
            Log.d(TAG, Thread.currentThread().toString());
            mProgressBar.setVisibility(ProgressBar.VISIBLE);
            ScanTask discovery = new ScanTask(btAdapter, this); //ScanTask discovery = new ScanTask(btAdapter, this, mDevices); for no future
            discovery.setOnCompletedListener(new ScanTask.OnCompletedListener() {
                @Override
                public void onComplete() {
                    Log.d(TAG, Thread.currentThread().toString());
                    mProgressBar.setVisibility(ProgressBar.GONE);
                    mDevices = discovery.getDevices();
                }
            });
            Log.d(TAG, "after setVisibilty");
            pool.submit(discovery);
            break;
    }

    return true;
}

更新UI线程时可调用块

0 个答案: