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我正在编写一个 Android 应用程序，我想在调用浏览器显示流之前确保无线已连接，但是当单击按钮表示应用程序已停止运行时，它只会关闭。我已经在 android 清单文件中设置了权限。这是我的代码。在一个名为 Networking 的单独课程中，我这样做了。

public class Networking extends Main {

    public boolean  isWirelessConnected()
    {
        cm = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE); 
    NetworkInfo mwifi = cm.getNetworkInfo(ConnectivityManager.TYPE_WIFI);
    if(mwifi == null)
        return false;
    else 
        return true;
    }
    public void messageDialog()
    {
        AlertDialog.Builder alrtBuild = new AlertDialog.Builder(this);
        alrtBuild
        .setTitle("Wireless")
        .setMessage("You are not Connected would you like to Connect to wireless?")
        .setNegativeButton("Yes", new  DialogInterface.OnClickListener() {

            public void onClick(DialogInterface dialog, int which) {
                WifiManager wifiManger = (WifiManager) getSystemService(Context.WIFI_SERVICE);
                wifiManger.setWifiEnabled(true);

            }
        })
        .setNegativeButton("No", new DialogInterface.OnClickListener() {

            public void onClick(DialogInterface dialog, int which) {
                dialog.cancel();

            }
        });
        AlertDialog alert = alrtBuild.create();
        alert.show();


    }
}

在我的主要课程中

Networking netwrk = new Networking();
if(netwrk.wireless().isConnected())
{
    Intent brwoserIntent = new Intent(Intent.ACTION_VIEW,
             Uri.parse("http://www.own3d.tv/HotshotGG"));
    startActivity(brwoserIntent);               
}

这是我按下按钮时程序抛出的错误

12-08 19:51:16.904: E/AndroidRuntime(1549): FATAL EXCEPTION: main
12-08 19:51:16.904: E/AndroidRuntime(1549): java.lang.IllegalStateException: Could not execute method of the activity
12-08 19:51:16.904: E/AndroidRuntime(1549):     at android.view.View$1.onClick(View.java:3597)
12-08 19:51:16.904: E/AndroidRuntime(1549):     at android.view.View.performClick(View.java:4202)
12-08 19:51:16.904: E/AndroidRuntime(1549):     at android.view.View$PerformClick.run(View.java:17340)
12-08 19:51:16.904: E/AndroidRuntime(1549):     at android.os.Handler.handleCallback(Handler.java:725)
12-08 19:51:16.904: E/AndroidRuntime(1549):     at android.os.Handler.dispatchMessage(Handler.java:92)
12-08 19:51:16.904: E/AndroidRuntime(1549):     at android.os.Looper.loop(Looper.java:137)
12-08 19:51:16.904: E/AndroidRuntime(1549):     at android.app.ActivityThread.main(ActivityThread.java:5039)
12-08 19:51:16.904: E/AndroidRuntime(1549):     at java.lang.reflect.Method.invokeNative(Native Method)
12-08 19:51:16.904: E/AndroidRuntime(1549):     at java.lang.reflect.Method.invoke(Method.java:511)
12-08 19:51:16.904: E/AndroidRuntime(1549):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
12-08 19:51:16.904: E/AndroidRuntime(1549):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
12-08 19:51:16.904: E/AndroidRuntime(1549):     at dalvik.system.NativeStart.main(Native Method)
12-08 19:51:16.904: E/AndroidRuntime(1549): Caused by: java.lang.reflect.InvocationTargetException
12-08 19:51:16.904: E/AndroidRuntime(1549):     at java.lang.reflect.Method.invokeNative(Native Method)
12-08 19:51:16.904: E/AndroidRuntime(1549):     at java.lang.reflect.Method.invoke(Method.java:511)
12-08 19:51:16.904: E/AndroidRuntime(1549):     at android.view.View$1.onClick(View.java:3592)
12-08 19:51:16.904: E/AndroidRuntime(1549):     ... 11 more
12-08 19:51:16.904: E/AndroidRuntime(1549): Caused by: java.lang.IllegalStateException: System services not available to Activities before onCreate()
12-08 19:51:16.904: E/AndroidRuntime(1549):     at android.app.Activity.getSystemService(Activity.java:4463)
12-08 19:51:16.904: E/AndroidRuntime(1549):     at nc.prog1415.Networking.isWirelessConnected(Networking.java:14)
12-08 19:51:16.904: E/AndroidRuntime(1549):     at nc.prog1415.Main.hotshotBtns(Main.java:109)
12-08 19:51:16.904: E/AndroidRuntime(1549):     ... 14 more
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2 回答 2

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很可能netwrk.wireless()是返回 null 并导致NullPointerException.

我会将您的wireless()方法更改isWirelessConnected()为如下

public boolean isWirelessConnected() {
    ConnectivityManager cm = (ConnectivityManager)getSystemService(Context.CONNECTIVITY_SERVICE); 
       NetworkInfo mwifi = cm.getNetworkInfo(ConnectivityManager.TYPE_WIFI);

    if ( mwifi == null )
        return false;
    else
        return mwifi.isConnected();
}

然后在主类中，只需执行

Networking netwrk = new Networking();
if( netwrk.isWirelessConnected() ) {
    Intent brwoserIntent = new Intent(Intent.ACTION_VIEW, Uri.parse("http://www.own3d.tv/HotshotGG"));
    startActivity(brwoserIntent); 
}
于 2012-12-08T19:37:17.670 回答
0

来自 LogCat：

系统服务在之前的活动中不可用onCreate()

这个错误是不言自明的，所以把你的代码改成这样：

ConnectivityManager cm; 

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    cm = (ConnectivityManager)getSystemService(Context.CONNECTIVITY_SERVICE);
    ...
}

此外
，您的网络扩展了 Main，我认为这是一个 Activity。既然你不想要你正在做的事情的完整活动，你应该采取不同的策略。您应该在构造函数中传递 Networking a Context ：

public class Networking {
    Context context;

    public Networking(Context con) {
        context = con;
    }

    public boolean isWirelessConnected()
    {
        cm = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE); 
        NetworkInfo mwifi = cm.getNetworkInfo(ConnectivityManager.TYPE_WIFI);
        if(mwifi == null)
            return false;
        else 
            return mwifi.isConnectedOrConnecting();
    }

    // etc
}

请注意，我切换到context.getSystemService()您在创建对话框时也需要这样做。

现在改变你使用这个方法的方式：

Networking netwrk = new Networking(this);
if(netwrk.isWirelessConnected())
于 2012-12-08T20:11:19.987 回答