Question

我遇到以下错误：任何人都可以解决此问题

调试器： AdroidRuntime：致命异常：主要进程：com.example.avishek.wifidirect，PID：8053 java.lang.RuntimeException：无法启动活动 ComponentInfo {com.example.avishek.wifidirect / com.example.avishek.wifidirect.MainActivity}：java.lang .NullPointerException：尝试调用虚拟方法'android.net.wifi.p2p.WifiP2pManager $ Channel android.net.wifi.p2p.WifiP2pManager.initialize（android.content.Context，android.os.Looper，android.net.wifi。 p2p.WifiP2pManager $ ChannelListener）'对空对象引用

MainActivity.java

中此行发生此错误

    mChannel= mManager.initialize(this, Looper.getMainLooper(),null);

activity_main.xml中

 <?xml version="1.0" encoding="utf-8"?>
 <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">

<Button
    android:id="@+id/onOff"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentStart="true"
    android:layout_alignParentTop="true"
    android:layout_marginStart="28dp"
    android:layout_marginTop="55dp"
    android:text="Wifi On" />

<Button
    android:id="@+id/discover"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignBaseline="@+id/onOff"
    android:layout_alignBottom="@+id/onOff"
    android:layout_centerHorizontal="true"
    android:text="discover" />

<ListView
    android:id="@+id/peerListView"
    android:layout_width="match_parent"
    android:layout_height="200dp"
    android:layout_alignParentStart="true"
    android:layout_below="@+id/onOff"
    android:layout_marginTop="25dp"
    android:background="@android:color/holo_orange_light" />

<TextView
    android:id="@+id/readMsg"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentEnd="true"
    android:layout_alignParentStart="true"
    android:layout_below="@+id/peerListView"
    android:layout_marginTop="31dp"
    android:text="Message"
    android:textAlignment="center"
    android:textSize="20sp"
    android:textStyle="italic" />

<EditText
    android:id="@+id/writeMsg"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentBottom="true"
    android:layout_alignParentStart="true"
    android:ems="10"
    android:inputType="textPersonName"
    android:layout_toStartOf="@+id/sendButton" />

<Button
    android:id="@+id/sendButton"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentBottom="true"
    android:layout_alignParentEnd="true"
    android:text="Send" />

<TextView
    android:id="@+id/connectionStatus"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_alignParentStart="true"
    android:layout_alignParentTop="true"
    android:layout_marginTop="15dp"
    android:text="Connection Status"
    android:textAlignment="center"
    android:textColor="@android:color/holo_blue_dark"
    android:textSize="18sp"
    android:textStyle="italic" />

MainActivity.java

  package com.example.avishek.wifidirect;

  import android.content.BroadcastReceiver;
   import android.content.Context;
    import android.content.IntentFilter;
   import android.net.wifi.WifiManager;
   import android.net.wifi.p2p.WifiP2pManager;
   import android.os.Looper;
   import android.support.v7.app.AppCompatActivity;
   import android.os.Bundle;
   import android.view.View;
   import android.widget.Button;
   import android.widget.EditText;
   import android.widget.ListView;
   import android.widget.TextView;

   import android.net.wifi.p2p.WifiP2pManager.Channel;

    public class MainActivity extends AppCompatActivity {



Button btnwifid,btnsearch, btnsend;
ListView listView;
TextView read_msg_box, ConnectionStatus;
EditText writeMsg;

WifiManager wifiManager;
WifiP2pManager mManager;
Channel mChannel;


BroadcastReceiver mReceiver;
IntentFilter mIntentFilter;



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

    initialWork();
    exqListener();
}

private void exqListener() {
    btnwifid.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            if (wifiManager.isWifiEnabled())
            {
                wifiManager.setWifiEnabled(false);
                btnwifid.setText("ON");

            }else{
                wifiManager.setWifiEnabled(true);
                btnwifid.setText("OFF");
            }
        }
    });
}

private void initialWork() {


    btnwifid=(Button) findViewById(R.id.onOff);
    btnsearch=(Button) findViewById(R.id.discover);
    btnsend=(Button) findViewById(R.id.sendButton);
    listView=(ListView) findViewById(R.id.peerListView);
    read_msg_box=(TextView) findViewById(R.id.readMsg);
    ConnectionStatus=(TextView) findViewById(R.id.connectionStatus);
    writeMsg=(EditText) findViewById(R.id.writeMsg);
    wifiManager= (WifiManager) getApplicationContext().getSystemService(Context.WIFI_SERVICE);


    mManager= (WifiP2pManager) getSystemService(Context.WIFI_P2P_SERVICE);
    //mChannel=mManager.initialize(this,getMainLooper(),null);
    mChannel= mManager.initialize(this, getMainLooper(),null);
    //mChannel=mManager.initialize(this,getMainLooper(),null);


    mReceiver=new WiFiDirectBroadcastReceiver(mManager,mChannel,this,this);
    mIntentFilter=new IntentFilter();

    mIntentFilter.addAction(WifiP2pManager.WIFI_P2P_STATE_CHANGED_ACTION);
    mIntentFilter.addAction(WifiP2pManager.WIFI_P2P_PEERS_CHANGED_ACTION);
    mIntentFilter.addAction(WifiP2pManager.WIFI_P2P_CONNECTION_CHANGED_ACTION);
    mIntentFilter.addAction(WifiP2pManager.WIFI_P2P_THIS_DEVICE_CHANGED_ACTION);




}

@Override
protected void onResume() {
    super.onResume();
    registerReceiver(mReceiver,mIntentFilter);
}

@Override
protected void onPause() {
    super.onPause();
    unregisterReceiver(mReceiver);
}
   }

WiFiDirectBroadcastReceiver

    package com.example.avishek.wifidirect;

 import android.content.BroadcastReceiver;
  import android.content.Context;
 import android.content.Intent;
 import android.net.wifi.p2p.WifiP2pManager;

 import android.widget.Toast;
 import android.net.wifi.p2p.WifiP2pManager.Channel;

public class WiFiDirectBroadcastReceiver extends BroadcastReceiver {
     private Context context;
     private WifiP2pManager mManager;
     private Channel mChannel;
     private MainActivity mActivity;


  public WiFiDirectBroadcastReceiver(WifiP2pManager mManager, Channel                   mChannel,MainActivity ,mActivity ,Context context)
{   super();
    this.mManager =mManager;
    this.mChannel =mChannel;
    this.mActivity=mActivity;
    this.context=context;



}


@Override
public void onReceive(Context context, Intent intent) {
    String action = intent.getAction();


    if(WifiP2pManager.WIFI_P2P_STATE_CHANGED_ACTION.equals(action)){
        int state=intent.getIntExtra(WifiP2pManager.EXTRA_WIFI_STATE,-1);

        if(state==WifiP2pManager.WIFI_P2P_STATE_ENABLED){


            Toast.makeText(context,"Wifi is On", Toast.LENGTH_SHORT).show();
        }else{

            Toast.makeText(context,"WiFi is Off",Toast.LENGTH_SHORT).show();}

    }else if(WifiP2pManager.WIFI_P2P_PEERS_CHANGED_ACTION.equals(action)){
        //do
    }else if (WifiP2pManager.WIFI_P2P_CONNECTION_CHANGED_ACTION.equals(action)){
        //do
    }else if (WifiP2pManager.WIFI_P2P_THIS_DEVICE_CHANGED_ACTION.equals(action)){
        //do
    }

}
    }

的AndroidManifest.xml

     <?xml version="1.0" encoding="utf-8"?>
   <manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.avishek.wifidirect">

  <uses-permission android:name="android.permission.ACCESS_WIFI_STATE"/>
<uses-permission android:name="android.permission.CHANGE_WIFI_STATE"/>
<uses-permission android:name="android.permission.CHANGE_NETWORK_STATE"/>
<uses-permission android:name="android.permission.INTERNET"/>
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>



<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:roundIcon="@mipmap/ic_launcher_round"
    android:supportsRtl="true"
    android:theme="@style/AppTheme">
    <activity android:name=".MainActivity">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
</application>

Answer 1

您错过了AndroidManifest.xml中的uses-feature：

<uses-feature android:name="android.hardware.wifi.direct" android:required="true"/>

Android SDK Null点异常

1 个答案: