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我正在尝试构建一个扫描本地 Miracast 连接并连接到它们以自动镜像屏幕的 Android 应用程序。我还希望能够保存用户之前已经连接过的连接并给他们起昵称，这样用户就可以更容易地识别它们。我几乎没有任何 Android 开发经验，但我在 Java 和其他语言方面有多年经验。

现在，我遇到的问题是当我尝试在 MainActivity 的 OnCreate 方法中设置适配器时，我的 ListView 返回一个空指针异常。

MainActivity.java 

import java.io.IOException;
import java.net.InetAddress;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.ArrayList;
import java.util.Collection;

import android.app.Fragment;
import android.app.Presentation;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.content.SharedPreferences;
import android.content.SharedPreferences.OnSharedPreferenceChangeListener;
import android.hardware.display.DisplayManager;
import android.media.MediaRouter;
import android.net.NetworkInfo;
import android.net.wifi.WpsInfo;
import android.net.wifi.p2p.WifiP2pConfig;
import android.net.wifi.p2p.WifiP2pDevice;
import android.net.wifi.p2p.WifiP2pDeviceList;
import android.net.wifi.p2p.WifiP2pGroup;
import android.net.wifi.p2p.WifiP2pInfo;
import android.net.wifi.p2p.WifiP2pManager;
import android.net.wifi.p2p.WifiP2pManager.ActionListener;
import android.net.wifi.p2p.WifiP2pManager.Channel;
import android.net.wifi.p2p.WifiP2pManager.ChannelListener;
import android.net.wifi.p2p.WifiP2pManager.GroupInfoListener;
import android.net.wifi.p2p.WifiP2pManager.PeerListListener;
import android.os.Bundle;
import android.support.v4.app.DialogFragment;
import android.support.v4.app.FragmentActivity;
import android.util.Log;
import android.view.Display;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.CheckBox;
import android.widget.ListView;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends FragmentActivity implements OnSharedPreferenceChangeListener{

public static final String TAG = "MainActivity";
private MediaRouter mMediaRouter;
private WifiP2pManager wifimngr; 
protected Channel channel;
private boolean paused = false;
private boolean connected = false;
private boolean scanning = false;
protected boolean isWifiEnabled;
protected boolean onCharge;
protected boolean onAlways;
protected MyBroadcastReceiver receiver;
protected ArrayList<WifiP2pDevice> connectionList;
protected int listsize;
private DisplayManager mDisplayManager;
protected ConnectionAdapter adapter;
protected ArrayList<WifiP2pDevice> devices;
private final IntentFilter intentFilter = new IntentFilter();

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

    connectionList = new ArrayList<WifiP2pDevice>();
    adapter = new ConnectionAdapter(this, devices);
    ListView listview = (ListView) findViewById(R.id.list);
    listview.setAdapter(adapter);

    //Connection newCon = new Connection("My address", "My nickname", false);
    //adapter.add(newCon);
    //newCon = new Connection("My address2", "My nickname2", true);
    //adapter.add(newCon);

    //  Indicates a change in the Wi-Fi P2P status.
    intentFilter.addAction(WifiP2pManager.WIFI_P2P_STATE_CHANGED_ACTION);

    // Indicates a change in the list of available peers.
    intentFilter.addAction(WifiP2pManager.WIFI_P2P_PEERS_CHANGED_ACTION);

    // Indicates the state of Wi-Fi P2P connectivity has changed.
    intentFilter.addAction(WifiP2pManager.WIFI_P2P_CONNECTION_CHANGED_ACTION);

    // Indicates this device's details have changed.
    intentFilter.addAction(WifiP2pManager.WIFI_P2P_THIS_DEVICE_CHANGED_ACTION);


    mDisplayManager = (DisplayManager)this.getSystemService(Context.DISPLAY_SERVICE);
    if (savedInstanceState == null) {
        getFragmentManager().beginTransaction()
                .add(R.id.container, new PlaceholderFragment())
                .commit();
    }

    wifimngr = (WifiP2pManager)getSystemService(Context.WIFI_P2P_SERVICE);
    channel  = wifimngr.initialize(this, getMainLooper(), new ChannelListener() {
        public void onChannelDisconnected() {
            channel = null;
        }
    });

}

PeerListListener myPeerListListener =
           new PeerListListener() {
                @Override
                public void onPeersAvailable(WifiP2pDeviceList peerList) {

                    // Out with the old, in with the new.
                    devices.clear();
                    devices.addAll(peerList.getDeviceList());

                    // If an AdapterView is backed by this data, notify it
                    // of the change.  For instance, if you have a ListView of available
                    // peers, trigger an update.
                    //((ConnectionAdapter) getListAdapter()).notifyDataSetChanged();
                    if (devices.size() == 0) {
                        Log.d("TAG", "No devices found");
                        return;
                    }
                }

        };

@Override
public boolean onCreateOptionsMenu(Menu menu) {

    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();
    if (id == R.id.action_settings) {
        openSettings();
        return true;
    }
    return super.onOptionsItemSelected(item);
}

/**
 * A placeholder fragment containing a simple view.
 */
public static class PlaceholderFragment extends Fragment {

    public PlaceholderFragment() {
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_main, container, false);
        return rootView;
    }
}

public void updateStatus(String input)
{
    TextView edit = (TextView) findViewById(R.id.statusText);
    edit.setText(input);
}

//What happens when the pause button is clicked
public void pauseConnections(View view)
{
    if(!paused)
    {
        updateStatus("Streaming");
        mMediaRouter = (MediaRouter) this.getSystemService(Context.MEDIA_ROUTER_SERVICE);

         MediaRouter.RouteInfo route = mMediaRouter.getSelectedRoute(mMediaRouter.ROUTE_TYPE_LIVE_VIDEO);
         if (route != null) {
             Display presentationDisplay = route.getPresentationDisplay();
             if (presentationDisplay != null) {
                 Presentation presentation = new Presentation(this, presentationDisplay, 0);
                 presentation.show();
             }
         }
        ProgressBar pg = (ProgressBar) findViewById(R.id.progressBar1);
        pg.setVisibility(View.VISIBLE);
        Button edit = (Button) findViewById(R.id.pauseButton);
        edit.setText("Pause");
        edit = (Button) findViewById(R.id.scanbutton);
        edit.setEnabled(false);
    }else
    {
        updateStatus("Paused");


         MediaRouter.RouteInfo route = mMediaRouter.getSelectedRoute(mMediaRouter.ROUTE_TYPE_LIVE_VIDEO);
         if (route != null) {
             Display presentationDisplay = route.getPresentationDisplay();
             if (presentationDisplay != null) {
                 Presentation presentation = new Presentation(this, presentationDisplay, 0);
                 presentation.show();
             }
         }
        ProgressBar pg = (ProgressBar) findViewById(R.id.progressBar1);
        pg.setVisibility(View.INVISIBLE);
        Button edit = (Button) findViewById(R.id.pauseButton);
        edit.setText("Stream");
        edit = (Button) findViewById(R.id.scanbutton);
        edit.setEnabled(true);
    }
    paused=!paused;


}

//What happens when the scan button is clicked
public void scanConnections(View view)
{

    if(!scanning)
    {

        updateStatus("Scanning...");
        ProgressBar pg = (ProgressBar) findViewById(R.id.progressBar1);
        pg.setVisibility(View.VISIBLE);
        wifimngr.setMiracastMode(1);
        wifimngr.discoverPeers(channel, new WifiP2pManager.ActionListener() {

            @Override
            public void onSuccess() {

            }

            @Override
            public void onFailure(int reason) {
                if(reason == 1)
                {
                    updateStatus("Failed to get devices. Device not supported");

                }else if(reason == 2)
                {
                    updateStatus("Failed to get devices. Busy");
                }else
                {
                    updateStatus("Failed to get devices. Error");
                }
                ProgressBar pg = (ProgressBar) findViewById(R.id.progressBar1);
                pg.setVisibility(View.INVISIBLE);
                Button edit = (Button) findViewById(R.id.scanbutton);
                edit.setText("Scan");
                edit = (Button) findViewById(R.id.pauseButton);
                edit.setEnabled(true);
                scanning=!scanning;

            }
        });

        Button edit = (Button) findViewById(R.id.scanbutton);
        edit.setText("Stop");
        edit = (Button) findViewById(R.id.pauseButton);
        edit.setEnabled(false);
    }else
    {

        ProgressBar pg = (ProgressBar) findViewById(R.id.progressBar1);
        pg.setVisibility(View.INVISIBLE);
        wifimngr.removeGroup(channel, new WifiP2pManager.ActionListener() {

            @Override
            public void onSuccess() {


            }

            @Override
            public void onFailure(int reason) {
                if(reason == 1)
                {
                    updateStatus("Failed to disconnect. Device not supported");

                }else if(reason == 2)
                {
                    updateStatus("Failed to disconnect. Busy");
                }else
                {
                    updateStatus("Failed to disconnect. Error");
                }
                ProgressBar pg = (ProgressBar) findViewById(R.id.progressBar1);
                pg.setVisibility(View.INVISIBLE);

            }
        });         

        updateStatus("Waiting");
        Button edit = (Button) findViewById(R.id.scanbutton);
        edit.setText("Scan");
        edit = (Button) findViewById(R.id.pauseButton);
        edit.setEnabled(true);
    }
    scanning=!scanning;
}

public void openSettings()
{
    Intent intent = new Intent(this, SettingsActivity.class);
    intent.putExtra("onCharge", onCharge);
    intent.putExtra("onAlways", onAlways);
    startActivity(intent);

}

public void onCheckboxClicked(View view)
{
    boolean checked = ((CheckBox) view).isChecked();

}

public void onConnectionClick(View view)
{
    DialogFragment dialog = new ConnDialogFragment();
    dialog.show(getSupportFragmentManager(), "NoticeDialogFragment");

}

public void onSharedPreferenceChanged(SharedPreferences sharedPreferences,
        String key) {
        if (key.equals("pref_onCharge")) {

            // Set summary to be the user-description for the selected value
            onCharge = sharedPreferences.getBoolean(key, true);
        }else if (key.equals("pref_onAlways")) {

            // Set summary to be the user-description for the selected value
            onAlways = sharedPreferences.getBoolean(key, false);
        }else if(key.equals("pref_listsize"))
        {
            listsize = sharedPreferences.getInt(key, 0);
        }
    }

private void onPeersChanged(Intent intent)
{
    wifimngr.requestPeers(channel, myPeerListListener);
}

private void onConnectionChanged(Intent intent) {
    WifiP2pInfo p2pInfo = intent.getParcelableExtra(WifiP2pManager.EXTRA_WIFI_P2P_INFO);
    NetworkInfo netInfo = intent.getParcelableExtra(WifiP2pManager.EXTRA_NETWORK_INFO);
    if (netInfo.isConnected()) 
    {
        updateInfos();
        useNetwork(p2pInfo);
    } else 
    {
        //resetInfos();
    }
}


public void connect() {
    // Picking the first device found on the network.
    WifiP2pDevice device = devices.get(0);

    WifiP2pConfig config = new WifiP2pConfig();
    config.deviceAddress = device.deviceAddress;
    config.wps.setup = WpsInfo.PBC;

    wifimngr.connect(channel, config, new ActionListener() {

        @Override
        public void onSuccess() {
            // WiFiDirectBroadcastReceiver will notify us. Ignore for now.
        }

        @Override
        public void onFailure(int reason) {
            Toast.makeText(MainActivity.this, "Connect failed. Retry.",
                    Toast.LENGTH_SHORT).show();
        }
    });
}


public void onConnectionInfoAvailable(final WifiP2pInfo info) {

    // InetAddress from WifiP2pInfo struct.
    InetAddress groupOwnerAddress = info.groupOwnerAddress;

    // After the group negotiation, we can determine the group owner.
    if (info.groupFormed && info.isGroupOwner) {
        // Do whatever tasks are specific to the group owner.
        // One common case is creating a server thread and accepting
        // incoming connections.
    } else if (info.groupFormed) {
        // The other device acts as the client. In this case,
        // you'll want to create a client thread that connects to the group
        // owner.
    }
}


private void updateInfos() {
    wifimngr.requestGroupInfo(channel,
       new GroupInfoListener() {
        @Override
        public void onGroupInfoAvailable(WifiP2pGroup group)
       {
            String name = group.getNetworkName();
            String passphrase = group.getPassphrase();
            Collection<WifiP2pDevice> devices = group.getClientList();
                    // do stuff with devices
                    // but ... No way to get their IP addresses :(
        }
    });
}

private void useNetwork(WifiP2pInfo p2pInfo) {
    if (!p2pInfo.isGroupOwner) {
        InetAddress addr  = p2pInfo.groupOwnerAddress;
        try
        {
            Socket s  = new Socket(addr, 1234);
        }catch(IOException e)
        {
            e.printStackTrace();
        }

         //use the socket
    } else {
        try{
             //groupOwnerAddress is our local address
             ServerSocket serverSocket = new ServerSocket(1234);
            Socket s  = serverSocket.accept();
            }catch(IOException e)
            {
                e.printStackTrace();
            }
         //use the socket
    }
}

private void connect(WifiP2pDevice device) {
    WifiP2pConfig config = new WifiP2pConfig();
    config.deviceAddress = device.deviceAddress;
    config.wps.setup = WpsInfo.PBC; // choose between what is available on the device.
    wifimngr.connect(channel, config, new WifiP2pManager.ActionListener() {

        @Override
        public void onSuccess() {

        }

        @Override
        public void onFailure(int reason) {


        }
    });
}

protected void setIsWifiP2pEnabled(boolean isEnabled)
{
    isWifiEnabled = isEnabled;
}

/** register the BroadcastReceiver with the intent values to be matched */
@Override
public void onResume() {
    super.onResume();
    receiver = new MyBroadcastReceiver(wifimngr, channel, this);
    registerReceiver(receiver, intentFilter);
}

@Override
public void onPause() {
    super.onPause();
    unregisterReceiver(receiver);
}


}

连接适配器.java

    import java.util.ArrayList;

    import android.content.Context;
    import android.net.wifi.p2p.WifiP2pDevice;
    import android.view.LayoutInflater;
    import android.view.View;
    import android.view.ViewGroup;
    import android.widget.ArrayAdapter;
    import android.widget.TextView;

    public class ConnectionAdapter extends ArrayAdapter<WifiP2pDevice> {

    public ConnectionAdapter(Context context, ArrayList<WifiP2pDevice> connections)
    {
        super(context, R.layout.connection, connections);
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
       // Get the data item for this position
        WifiP2pDevice con = getItem(position);    
       // Check if an existing view is being reused, otherwise inflate the view
       ViewHolder viewHolder; 

       if (convertView == null) {
          viewHolder = new ViewHolder();
          LayoutInflater inflater = LayoutInflater.from(getContext());
          convertView = inflater.inflate(R.layout.connection, parent, false);
          viewHolder.name = (TextView) convertView.findViewById(R.id.conName);
          viewHolder.nickname = (TextView) convertView.findViewById(R.id.conNickname);
          convertView.setTag(viewHolder);
       }else {
           viewHolder = (ViewHolder) convertView.getTag();
       }

       // Populate the data into the template view using the data object
       viewHolder.name.setText(con.deviceName);
       viewHolder.nickname.setText(con.primaryDeviceType);
       // Return the completed view to render on screen
       return convertView;
    }

     private static class ViewHolder {
            TextView name;
            TextView nickname;
        }
    }


**BroadcastReceiver.java**


    import android.content.BroadcastReceiver;
    import android.content.Context;
    import android.content.Intent;
    import android.net.NetworkInfo;
    import android.net.wifi.p2p.WifiP2pDevice;
    import android.net.wifi.p2p.WifiP2pManager;
    import android.net.wifi.p2p.WifiP2pManager.Channel;
    import android.net.wifi.p2p.WifiP2pManager.PeerListListener;
    import android.util.Log;

    public class MyBroadcastReceiver extends BroadcastReceiver{

    protected WifiP2pManager wifimngr;
    protected Channel channel;
    protected MainActivity activity;

    public MyBroadcastReceiver(WifiP2pManager iwifimngr, Channel ichannel, MainActivity iactivity)
    {
        super();
        wifimngr=iwifimngr;
        channel=ichannel;
        activity=iactivity;
    }

    @Override
    public void onReceive(Context context, Intent intent) {
        String action = intent.getAction();
        if (WifiP2pManager.WIFI_P2P_STATE_CHANGED_ACTION.equals(action)) {
            // Determine if Wifi P2P mode is enabled or not, alert
            // the Activity.
            int state = intent.getIntExtra(WifiP2pManager.EXTRA_WIFI_STATE, -1);
            if (state == WifiP2pManager.WIFI_P2P_STATE_ENABLED) {
                activity.setIsWifiP2pEnabled(true);
            } else {
                activity.setIsWifiP2pEnabled(false);
            }
        } else if (WifiP2pManager.WIFI_P2P_PEERS_CHANGED_ACTION.equals(action)) {

            // Request available peers from the wifi p2p manager. This is an
            // asynchronous call and the calling activity is notified with a
            // callback on PeerListListener.onPeersAvailable()
            if (wifimngr != null) {
                wifimngr.requestPeers(channel, (PeerListListener) activity.getFragmentManager()
                         .findFragmentById(R.id.list));
            }
            Log.d(MainActivity.TAG, "P2P peers changed");


        } else if (WifiP2pManager.WIFI_P2P_CONNECTION_CHANGED_ACTION.equals(action)) {

            if (wifimngr == null) {
                return;
            }

            NetworkInfo networkInfo = (NetworkInfo) intent
                    .getParcelableExtra(WifiP2pManager.EXTRA_NETWORK_INFO);

            if (networkInfo.isConnected()) {

                // we are connected with the other device, request connection
                // info to find group owner IP

               //DeviceDetailFragment fragment = (DeviceDetailFragment) activity
                //        .getFragmentManager().findFragmentById(R.id.frag_detail);
                //wifimngr.requestConnectionInfo(channel, fragment);
            } else {
                // It's a disconnect
                //activity.resetData();
            }

        } else if (WifiP2pManager.WIFI_P2P_THIS_DEVICE_CHANGED_ACTION.equals(action)) {
            DeviceListFragment fragment = (DeviceListFragment) activity.getFragmentManager()
                    .findFragmentById(R.id.list);
            fragment.updateThisDevice((WifiP2pDevice) intent.getParcelableExtra(
                    WifiP2pManager.EXTRA_WIFI_P2P_DEVICE));

        }
    }



    }

activity_main.xml

 <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.hpconcept.miracastconnector.MainActivity"
    tools:ignore="MergeRootFrame" >

    <ListView
        android:id="@+id/list"
        android:layout_width="wrap_content"
        android:layout_height="250dp"
        android:layout_marginTop="0dp"
        android:layout_marginBottom="0dp"
        android:paddingTop="0dp"
        android:textSize="20sp" >
    </ListView>

    <View android:id="@+id/strut"
        android:layout_width="0dp"
        android:layout_height="0dp" 
        android:layout_marginTop="200dp"
        android:layout_below="@android:id/list"
        android:layout_centerHorizontal="true"/>

    <Button
        android:id="@+id/scanbutton"
        android:text="@string/scan_string"
        android:layout_height="wrap_content"
        android:layout_below="@android:id/list"
        android:layout_width="0dp"
        android:layout_alignParentBottom="true"
        android:onClick="scanConnections"
        android:layout_alignRight="@id/strut"
        android:layout_alignParentLeft="true"
         />

    <Button
        android:id="@+id/pauseButton"
        android:text="@string/stream_string"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:onClick="pauseConnections"
        android:layout_gravity="bottom"
        android:layout_alignLeft="@id/strut"
        android:layout_alignParentRight="true"
        android:layout_alignParentBottom="true"
        android:layout_below="@android:id/list"
        android:layout_toRightOf="@+id/scanbutton" />

    <TextView
        android:id="@+id/statusText"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_above="@+id/pauseButton"
        android:layout_alignLeft="@+id/pauseButton"
        android:layout_marginLeft="42dp"
        android:gravity="center"
        android:text="@string/waiting_string" />

    <ProgressBar
        android:id="@+id/progressBar1"
        style="?android:attr/progressBarStyleSmall"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignBottom="@+id/statusText"
        android:layout_alignLeft="@+id/pauseButton"
        android:layout_marginLeft="24dp"
        android:visibility="invisible" />

    </RelativeLayout>

所以整个项目基本上变成了我试图将来自互联网的各种示例代码粘贴在一起。我真的可以使用一些帮助。我正在尝试使用 Google 的 Android 开发页面，但我并不总是知道将他们的代码片段放在哪里。我试图创建自己的 Connection 类，它将 WifiP2pDevice 与昵称和其他数据一起保存在数组列表中，但由于某种原因我无法让它工作。所以现在我的首要任务是让程序运行并找到连接。据我所知，我确实完成了 GUI。我可能需要改变它或其他东西。这不是我的全部代码。如果我全部发布，这个问题将是巨大的。大声笑如果你想看到这一切，让我知道。

4

1 回答 1

2

因此，我为任何感兴趣的人找到了此代码，并且效果很好：

try 
{
    Log.d("DEBUG", "open WiFi display settings in HTC");
    startActivity(new Intent("com.htc.wifidisplay.CONFIGURE_MODE_NORMAL"));
} catch (Exception e) 
{
    try 
    {
        Log.d("DEBUG", "open WiFi display settings in Samsung");
        startActivity(new Intent("com.samsung.wfd.LAUNCH_WFD_PICKER_DLG"));
    }catch (Exception e2) 
    {
        Log.d("DEBUG", "open WiFi display settings in stock Android");
        startActivity(new Intent("android.settings.WIFI_DISPLAY_SETTINGS"));
    }
}

我现在摆脱了列表视图，因为我不再需要使用 WifiP2p 扫描设备。当此设置打开时，它将自动连接到附近的显示器。

我唯一需要做的就是想办法让设置屏幕在连接到显示器后关闭。我曾尝试模拟后退按钮按下，但只有当用户自己返回应用程序时才会模拟。然后它退出应用程序。

于 2014-08-12T19:05:02.567 回答