java - 网络回调onAvailable方法中接口(interface)空指针异常

Question

下面是我的代码，我尝试实现接口(interface)来拦截来自 Connectivity Manager 网络回调的响应，但 Android Studio 在 onAvailable 方法中的该接口(interface) internetListener.onInternetStatusUpdate(true) 上抛出错误。

我还在我的主要 Activity 中实现了这个界面。我也遵循了一些例子，但失败了。是不是那个onAvailable方法，我的接口(interface)无法访问？

public class CheckInternetAsyncTask extends ConnectivityManager.NetworkCallback
{
    private static final String TAG = "CheckInternetAsyncTask";
    private Context context;
    public InternetListener internetListener;
    private ConnectivityManager connectivityManager;
    private Network network;
    private NetworkCapabilities networkCapabilities;

    public interface InternetListener{
        void onInternetStatusUpdate(boolean hasInternet);
    }

    public CheckInternetAsyncTask(Context _context) {
        this.context = _context;
        this.connectivityManager = (ConnectivityManager)context.getSystemService(Context.CONNECTIVITY_SERVICE);
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
            connectivityManager.registerDefaultNetworkCallback(this);
        }

        try {
            new SendInternetRequest().execute().get(5, TimeUnit.SECONDS);
        } catch (ExecutionException e) {
            e.printStackTrace();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (TimeoutException e) {
            e.printStackTrace();
        }
    }

    public void TestInternetRequest(){
        try {
            new SendInternetRequest().execute().get(5, TimeUnit.SECONDS);
        } catch (ExecutionException e) {
            e.printStackTrace();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (TimeoutException e) {
            e.printStackTrace();
        }
    }


    @Override
    public void onAvailable(Network network) {
        super.onAvailable(network);
        this.network = network;

        if(Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
            connectivityManager.bindProcessToNetwork(network);
            this.network = connectivityManager.getActiveNetwork();
        }else{
            ConnectivityManager.setProcessDefaultNetwork(network);
        }

        this.networkCapabilities = connectivityManager.getNetworkCapabilities(network);


        if(networkCapabilities != null && networkCapabilities.hasCapability(NetworkCapabilities.NET_CAPABILITY_INTERNET) && networkCapabilities.hasCapability(NetworkCapabilities.NET_CAPABILITY_VALIDATED)){
            internetListener.onInternetStatusUpdate(true);
        }else{
            try {
                new SendInternetRequest().execute().get(5, TimeUnit.SECONDS);
            } catch (ExecutionException e) {
                e.printStackTrace();
            } catch (InterruptedException e) {
                e.printStackTrace();
            } catch (TimeoutException e) {
                e.printStackTrace();
            }
        }
    }

class SendInternetRequest extends AsyncTask<Void,Void, Void>{
    private static final String TAG = "SendInternetRequest";

    CheckInternetAsyncTask.InternetListener internetListener;

    @Override
    protected Void doInBackground(Void... voids) {
        try {
            Socket sock = new Socket();
            sock.connect(new InetSocketAddress("8.8.8.8", 53), 1500);
            sock.close();
            internetListener.onInternetStatusUpdate(true);

        } catch (IOException e) {
            internetListener.onInternetStatusUpdate(false);
        }

        return null;
    }
}

堆栈跟踪

2019-09-25 10:08:02.566 29555-29578/com.kioskactionandnotification E/AndroidRuntime: FATAL EXCEPTION: ConnectivityThread
    Process: com.kioskactionandnotification, PID: 29555
    java.lang.NullPointerException: Attempt to invoke interface method 'void com.kioskactionandnotification.Model.Helper.CheckInternetAsyncTask$InternetListener.onInternetStatusUpdate(boolean)' on a null object reference
        at com.kioskactionandnotification.Model.Helper.CheckInternetAsyncTask.onAvailable(CheckInternetAsyncTask.java:85)
        at android.net.ConnectivityManager$NetworkCallback.onAvailable(ConnectivityManager.java:2770)
        at android.net.ConnectivityManager$CallbackHandler.handleMessage(ConnectivityManager.java:2969)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:193)
        at android.os.HandlerThread.run(HandlerThread.java:65)

MainActivity.java

我实现了接口(interface)

@Override
    public void onInternetStatusUpdate(boolean hasInternet) {
        this.hasInternet = hasInternet;
        Log.d(TAG, "onInternetStatusUpdate: hasInternet : "+hasInternet);
    }

这就是我所拥有的一切。

Answer 1

您似乎正在尝试访问 internetListener 类型的未初始化对象。

您需要初始化它:

internetListener = new InternetListener();

或者检查它是否已经初始化:

if (internetListener != null) {
 internetListener.onInternetStatusUpdate(true);
}

注意

您使用的任何抽象类都应该由子类扩展，该子类为抽象类中使用的任何抽象数据/方法提供实现。

Abstract class in Java