WiFi连接在机器人

改变动作我要开始我的应用程序时，WLAN将打开，这样我试图获得支持WiFi的国家行动改变功能但它显示WiFi连接在机器人

01-27 15:52:10.470: ERROR/AndroidRuntime(11584): java.lang.RuntimeException: Unable to instantiate receiver com.example.WiFiScanReceiver: java.lang.InstantiationException: com.example.WiFiScanReceiver

这是我的清单文件

<?xml version="1.0" encoding="utf-8"?> 
<manifest xmlns:android="http://schemas.android.com/apk/res/android" 
 package="com.example" android:versionCode="1" android:versionName="1.0"> 
 <application android:icon="@drawable/icon" android:label="@string/app_name" 
   android:theme="@android:style/Theme.Light"> 
   <activity android:name=".WiFiDemo" android:label="@string/app_name"> 
     <intent-filter> 
       <action android:name="android.intent.action.MAIN" /> 
       <category android:name="android.intent.category.LAUNCHER" /> 
     </intent-filter> 
   </activity> 
   <receiver android:name="com.example.WiFiScanReceiver"> 
     <intent-filter> 
       <action android:name="android.net.wifi.supplicant.CONNECTION_CHANGE" /> 
     </intent-filter> 
   </receiver> 
 </application> 
 <uses-sdk android:minSdkVersion="3" /> 
 <uses-permission android:name="android.permission.ACCESS_WIFI_STATE"></uses-permission> 
 <uses-permission android:name="android.permission.CHANGE_WIFI_STATE"></uses-permission> 
<uses-permission android:name="android.permission.UPDATE_DEVICE_STATS"></uses-permission> 
<uses-permission android:name="android.permission.CHANGE_NETWORK_STATE"> </uses-permission> 
<uses-permission android:name="android.permission.WAKE_LOCK"></uses-permission> 
<uses-permission android:name="android.permission.INTERNET" /> 
</manifest>

i fallow this link指导我如何开启我的活动，当wifi打开。

package com.example; 

import java.util.List; 

import android.app.Activity; 
import android.content.BroadcastReceiver; 
import android.content.Context; 
import android.content.IntentFilter; 
import android.net.wifi.WifiConfiguration; 
import android.net.wifi.WifiInfo; 
import android.net.wifi.WifiManager; 
import android.os.Bundle; 
import android.util.Log; 
import android.view.View; 
import android.view.View.OnClickListener; 
import android.widget.Button; 
import android.widget.TextView; 
import android.widget.Toast; 

public class WiFiDemo extends Activity implements OnClickListener { 
private static final String TAG = "WiFiDemo"; 
WifiManager wifi; 
BroadcastReceiver receiver; 

TextView textStatus; 
Button buttonScan; 

/** Called when the activity is first created. */ 
@Override 
public void onCreate(Bundle savedInstanceState) { 
 super.onCreate(savedInstanceState); 
 setContentView(R.layout.main); 

 // Setup UI 
 textStatus = (TextView) findViewById(R.id.textStatus); 
 buttonScan = (Button) findViewById(R.id.buttonScan); 
 buttonScan.setOnClickListener(this); 

 // Setup WiFi 
 wifi = (WifiManager) getSystemService(Context.WIFI_SERVICE); 

 // Get WiFi status 
 WifiInfo info = wifi.getConnectionInfo(); 
 textStatus.append("\n\nWiFi Status: " + info.toString()); 

 // List available networks 
 List<WifiConfiguration> configs = wifi.getConfiguredNetworks(); 
 for (WifiConfiguration config : configs) { 
  textStatus.append("\n\n" + config.toString()); 
 } 
  
 // Register Broadcast Receiver 
 if (receiver == null) 
  receiver = new WiFiScanReceiver(this); 

 registerReceiver(receiver, new IntentFilter(
   WifiManager.SCAN_RESULTS_AVAILABLE_ACTION)); 
 Log.d(TAG, "onCreate()"); 
} 

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

public void onClick(View view) { 
 Toast.makeText(this, "On Click Clicked. Toast to that!!!", 
   Toast.LENGTH_LONG).show(); 

 if (view.getId() == R.id.buttonScan) { 
  Log.d(TAG, "onClick() wifi.startScan()"); 
  wifi.startScan(); 
 } 
} 

}

这里是我的广播接收器的代码

package com.example; 

import java.util.List; 

import android.content.BroadcastReceiver; 
import android.content.Context; 
import android.content.Intent; 
import android.net.wifi.ScanResult; 
import android.net.wifi.WifiManager; 
import android.util.Log; 
import android.widget.Toast; 

public class WiFiScanReceiver extends BroadcastReceiver { 
 private static final String TAG = "WiFiScanReceiver"; 
 WiFiDemo wifiDemo; 

 public WiFiScanReceiver(WiFiDemo wifiDemo) { 
   super(); 
   this.wifiDemo = wifiDemo; 
 } 

 @Override 
 public void onReceive(Context c, Intent intent) { 
   List<ScanResult> results = wifiDemo.wifi.getScanResults(); 
   ScanResult bestSignal = null; 
final String action = intent.getAction(); 
   if (action.equals(WifiManager.SUPPLICANT_CONNECTION_CHANGE_ACTION)) { 
  System.out.println("booladsssssssssssssssssssssssssssssss"); 
  
 } 
   for (ScanResult result : results) { 
     if (bestSignal == null 
         || WifiManager.compareSignalLevel(bestSignal.level, result.level) < 0) 
       bestSignal = result; 
   } 

   String message = String.format("%s networks found. %s is the strongest.", 
       results.size(), bestSignal.SSID); 
   Toast.makeText(wifiDemo, message, Toast.LENGTH_LONG).show(); 

   Log.d(TAG, "onReceive() message: " + message); 
 } 

}

来源

2012-01-27 Gurumoorthy Arumugam

请发布您的WiFiDemo活动的来源。我猜测没有注册广播接收机。但是，除非你发布消息来源，否则我无法分辨。 :) – Jonathan 2012-01-27 10:39:53

@Jonathan现在我更新了我的代码.. – 2012-01-27 10:44:52

谢谢，我发布了一个答案，建议您将BroadcastReceiver实现移到匿名类中。然后，您将无需担心将参考传递给WiFiDemo活动。 – Jonathan 2012-01-27 12:26:23

您的接收器类没有默认构造函数。只有一个构造函数需要WiFiDemo，所以android无法弄清楚如何创建该类的实例。

更新：我想你对广播接收机的工作方式有点困惑。有两种方法：

你描述它在你的XML和Android将实例时，该事件发生的对象 - 在这种情况下，你需要一个默认的构造函数如public MyReceiver() {}而不是public MyReceiver(MyObject obj) {}
您在代码中注册您的广播接收器。这种类型可以有任何构造函数。

所以要解决你的问题。只需删除清单中广播接收器的减速度即可。

来源

2012-01-27 12:00:13 tidbeck

感谢您的评论，请你通过代码解释我。先谢谢你.. – 2012-01-27 14:00:55

@ user1105375好吧，现在阅读完整的代码和你遵循的教程。更新了答案。 – tidbeck 2012-01-27 16:01:02

Android将无法实例化该类，因为构造函数需要WiFiDemo。

为什么不让广播接收机匿名？

package com.example; 

    import java.util.List; 

    import android.app.Activity; 
    import android.content.BroadcastReceiver; 
    import android.content.Context; 
    import android.content.IntentFilter; 
    import android.net.wifi.WifiConfiguration; 
    import android.net.wifi.WifiInfo; 
    import android.net.wifi.WifiManager; 
    import android.os.Bundle; 
    import android.util.Log; 
    import android.view.View; 
    import android.view.View.OnClickListener; 
    import android.widget.Button; 
    import android.widget.TextView; 
    import android.widget.Toast; 

    public class WiFiDemo extends Activity implements OnClickListener { 
    private static final String TAG = "WiFiDemo"; 
    WifiManager wifi; 
    BroadcastReceiver receiver = new BroadcastReceiver(){ 
     @Override 
     public void onReceive(Context c, Intent intent) { 
      List<ScanResult> results = wifi.getScanResults(); 
      ScanResult bestSignal = null; 
      final String action = intent.getAction(); 
      if (action.equals(WifiManager.SUPPLICANT_CONNECTION_CHANGE_ACTION)) { 
       System.out.println("booladsssssssssssssssssssssssssssssss"); 

      } 
      for (ScanResult result : results) { 
       if (bestSignal == null || WifiManager.compareSignalLevel(bestSignal.level, result.level) < 0) 
         bestSignal = result; 
      } 

      String message = String.format("%s networks found. %s is the strongest.", 
      results.size(), bestSignal.SSID); 
      Toast.makeText(wifiDemo, message, Toast.LENGTH_LONG).show(); 

      Log.d(TAG, "onReceive() message: " + message); 
     } 

    }; 

    TextView textStatus; 
    Button buttonScan; 

    /** Called when the activity is first created. */ 
    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.main); 

     // Setup UI 
     textStatus = (TextView) findViewById(R.id.textStatus); 
     buttonScan = (Button) findViewById(R.id.buttonScan); 
     buttonScan.setOnClickListener(this); 

     // Setup WiFi 
     wifi = (WifiManager) getSystemService(Context.WIFI_SERVICE); 

     // Get WiFi status 
     WifiInfo info = wifi.getConnectionInfo(); 
     textStatus.append("\n\nWiFi Status: " + info.toString()); 

     // List available networks 
     List<WifiConfiguration> configs = wifi.getConfiguredNetworks(); 
     for (WifiConfiguration config : configs) { 
     textStatus.append("\n\n" + config.toString()); 
     } 

     // Register Broadcast Receiver   
     registerReceiver(receiver, new IntentFilter(
     WifiManager.SCAN_RESULTS_AVAILABLE_ACTION)); 
     Log.d(TAG, "onCreate()"); 
    } 

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

    public void onClick(View view) { 
     Toast.makeText(this, "On Click Clicked. Toast to that!!!", 
     Toast.LENGTH_LONG).show(); 

     if (view.getId() == R.id.buttonScan) { 
     Log.d(TAG, "onClick() wifi.startScan()"); 
     wifi.startScan(); 
     } 
    } 

    }

来源

2012-01-27 12:08:51 Jonathan

再次面临同样的错误01-27 18：03：26.500：E/AndroidRuntime（19704）：java.lang.RuntimeException：无法实例化接收器com.example.WiFiDemo：java.lang.ClassCastException：com.example.WiFiDemo can not be投射到android.content.BroadcastReceiver – 2012-01-27 12:34:52

什么是行号？这是一个不同的错误，顺便说一句。 – Jonathan 2012-01-27 12:40:59

发现错误，删除：'if（receiver == null）receiver = new WiFiScanReceiver（this）;' – Jonathan 2012-01-27 12:43:39

WiFi连接在机器人

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