我试图用getScanResults()显示WiFi的扫描结果。但是，当引用getScanResults的信息时，会发生崩溃。更详细地说，当添加的两行代码发生崩溃时:
if(results.size() > 0)
Toast.makeText(this, "Networks available!", Toast.LENGTH_LONG).show();
和代码段如下:
public void displayWifiNetworks(WifiManager wifi, ListView listView) {
List<ScanResult> results = wifi.getScanResults();
if(results.size() > 0)
Toast.makeText(this, "Networks available!", Toast.LENGTH_LONG).show();
我添加了<receiver>标记，其中动作标记包含在mainFest.xml中。但是，它在运行时仍然崩溃，警告"appname has stopped", java文件和mainFest.xml如下所示:'
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.connectivitymanager"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="16"
android:targetSdkVersion="17" />
<!-- add the permission to access and change the network state -->
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.CHANGE_NETWORK_STATE" />
<!-- add the permission to access and change the WiFi state -->
<uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
<uses-permission android:name="android.permission.CHANGE_WIFI_STATE" />
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name="com.example.connectivitymanager.MainActivity"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<!-- in order to access the WifiManage.getScanResults() -->
<receiver
android:name="com.example.connectivitymanager.MainActivity$WifiReceiver">
<intent-filter>
<action android:name="android.net.wifi.STATE_CHANGE"></action>
<action android:name="android.net.wifi.SCAN_RESULTS"></action>
</intent-filter>
</receiver>
</application>
Java文件
com.example.connectivitymanager;
public class MainActivity extends Activity {
private TextView viewText;
private Switch switchWiFiState;
WifiManager wifi;//this is used in WifiReceiver
WifiReceiver receiverWifi;
List<ScanResult> wifiList;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//display the initial state of the WiFi
String service = Context.CONNECTIVITY_SERVICE;
ConnectivityManager connectivity = (ConnectivityManager)getSystemService(service);
switchWiFiState = (Switch)findViewById(R.id.switch1);
if(connectivity.getNetworkInfo(ConnectivityManager.TYPE_WIFI).isConnected()) {
switchWiFiState.setChecked(true);
}
else
switchWiFiState.setChecked(false);
//change the state when thumb the switch back and force
switchWiFiState.setOnCheckedChangeListener(new OnCheckedChangeListener() {
@Override
public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
//update the WiFi state by the switch
String service = Context.WIFI_SERVICE;
wifi = (WifiManager)getSystemService(service);
receiverWifi = new WifiReceiver();
registerReceiver(receiverWifi, new IntentFilter(WifiManager.SCAN_RESULTS_AVAILABLE_ACTION));
wifi.startScan(); //startScan
if(isChecked) {
wifi.setWifiEnabled(true);
//when the WiFi is enabled, the available networks should be listed in ListView listAvailableNetworks
ListView listView = (ListView) findViewById(R.id.listAvailableNetworks);
displayWifiNetworks(wifi, listView);
}
else
wifi.setWifiEnabled(false);
}
});
}
public void displayWifiNetworks(WifiManager wifi, ListView listView) {
//Toast.makeText(this, "displaying WiFi information...", Toast.LENGTH_LONG).show();
//if(null != wifi.getScanResults().get(1).SSID)
List<ScanResult> results = wifi.getScanResults();
if(results.size() > 0)
Toast.makeText(this, "Networks available!", Toast.LENGTH_LONG).show();
}
@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;
}
//when click the displayConnectState button, the state is displayed in the textView
public void displayConnectState(View view) {
switch (view.getId()) {
case R.id.button1:
Toast.makeText(this, "Loading the connect info...", Toast.LENGTH_LONG).show();
String service = Context.CONNECTIVITY_SERVICE;
ConnectivityManager connectivity = (ConnectivityManager)getSystemService(service);
viewText = (TextView) findViewById(R.id.textView2);
viewText.setText(String.valueOf(connectivity.getNetworkInfo(ConnectivityManager.TYPE_WIFI).getDetailedState()));
break;
}
}
class WifiReceiver extends BroadcastReceiver {
@Override
public void onReceive(Context context, Intent intent) {
// TODO Auto-generated method stub
Toast.makeText(MainActivity.this, "in onReceive ...", Toast.LENGTH_LONG).show();
StringBuilder sb = new StringBuilder();
wifiList = wifi.getScanResults();
for(int i = 0; i< wifiList.size(); i++) {
System.out.println(wifiList.get(i).toString());
}
}
}
}
getScanResults()可以返回null，大多数情况下，因为您没有权限
<action android:name="android.net.wifi.WIFI_STATE_CHANGED"/>
<action android:name="android.net.wifi.SCAN_RESULTS"/>
/**
* Return the results of the latest access point scan.
* @return the list of access points found in the most recent scan.
*/
public List<ScanResult> getScanResults() {
try {
return mService.getScanResults();
} catch (RemoteException e) {
return null;
}
}
他们的坏，服务抛出了一个RemoteException，他们只是忽略它。我建议您每隔3秒重试一次以检索结果:
将WifiManager声明为类变量，并调用handler.post(wifiRunnable);而不是displayWifiNetworks。如果你离开Activity，在onPause()中你必须调用handler.removeCallbacks(null);
Handler handler = new Handler();
Runnable wifiRunnable = new Runnable() {
@Override
public void run() {
List<ScanResult> results = wifi.getScanResults();
if (results == null) {
handler.postDelayed(this, 3000);
return;
}
handler.removeCallbacks(this);
if(results.size() > 0)
Toast.makeText(this, "Networks available!", Toast.LENGTH_LONG).show();
}
}