Android网络连接

Question

有没有人能解释一下为什么我收到这个错误：

java.lang.RuntimeException: Unable to start activity
ComponentInfo{com.project/com.project.Deals}: java.lang.IllegalStateException: System services not available to Activities before onCreate() 

当我使用下面的两个类时，我已经这样做了很长时间了。我很感谢你的帮助

public class Deals extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        TextView textview = new TextView(this);
        textview.setText("This is the Artists tab");
        setContentView(textview);

        NetworkConnection nc = new NetworkConnection();
        boolean networkAvail = nc.isNetworkConnAvail();
        if (networkAvail == true){
        }

    }
};

public class NetworkConnection extends Activity {
/** Called when the activity is first created. */

public boolean isNetworkConnAvail() {

        ConnectivityManager connMgr = (ConnectivityManager) 
            getSystemService(Context.CONNECTIVITY_SERVICE);
        NetworkInfo networkInfo = connMgr.getActiveNetworkInfo();
        if (networkInfo != null)
            return networkInfo.isConnected();

        return false;
    }
}

Answer 1

问题出在您的NetworkConnection类中，您从未调用过onCreate，而是尝试这样做：

public boolean isNetworkConnAvail(Context context) {

    ConnectivityManager connMgr = (ConnectivityManager) 
        context.getSystemService(Context.CONNECTIVITY_SERVICE);
    NetworkInfo networkInfo = connMgr.getActiveNetworkInfo();
    if (networkInfo != null)
        return networkInfo.isConnected();

    return false;
}

在你的其他类中这样调用它：

nc.isNetworkConnAvail(this);

或者，在NetworkConnection的构造函数中调用超类的onCreate方法。如果您只是为了能够使用getSystemService而扩展Activity，那么您也可以不扩展Activity，而只是在构造函数或方法本身中传递上下文，因为这将使您能够访问这些方法:)

Answer 2

将此添加到您的清单中：

<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />

然后去掉这个：

extends Activity

在class NetworkConnection中

更新

更好的办法是将您的代码更改为：

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

boolean networkAvail = isNetworkConnAvail();
if (networkAvail == true){
  //do something
}

}

public boolean isNetworkConnAvail() {

ConnectivityManager connMgr = (ConnectivityManager) 
    getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo networkInfo = connMgr.getActiveNetworkInfo();
if (networkInfo != null)
    return networkInfo.isConnected();

return false;
}

}

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