Question

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，但是当单击按钮说明应用程序已停止运行时，它会关闭。我在android清单文件中设置了权限。这是我的代码。在一个名为Networking的单独类中，我这样做。

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();


    }
}

在主要课程中我有

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

Answer 1

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

我会将您的wireless()方法更改为isWirelessConnected()，如下所示

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();
}

然后在主课堂上，只需做

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

Answer 2

来自LogCat：

onCreate()
之前的活动无法使用的系统服务

此错误相当不言自明，因此请将代码更改为：

ConnectivityManager cm; 

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

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

<强>加成
您的网络扩展了Main，我认为它是一个Activity。既然你不想要一个完整的Activity来做你正在做的事情，你应该采取不同的策略。您应该在构造函数中传递Networking an 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，我在切换到context.getSystemService()时也需要在创建对话框时执行此操作。

现在改变使用此方法的方式：

Networking netwrk = new Networking(this);
if(netwrk.isWirelessConnected())

Android App在尝试访问无线时出错

2 个答案: