Android 'Unable to add window — token null is not for an application' 异常

Question

我正在尝试为网络变化实施观察者模式。我大致了解这是如何工作的，需要一些微调帮助，因为在尝试通知用户他们已失去连接时，我收到以下错误：

这是我的设置。首先，我有一个扩展 BroadcastReceiver 的 ConnectionReceiver class。

public class ConnectionReceiver extends BroadcastReceiver {
    private static final String TAG = ConnectionReceiver.class.getSimpleName();

    private final List<NetworkStatusObserver> mObserverList = new ArrayList<NetworkStatusObserver>();
    private static boolean isNetworkConnected = true;

    @Override
    public void onReceive(Context context, Intent intent) {
        Logger.i(TAG, "onReceive() broadcast");
        boolean disconnected = intent.getBooleanExtra(ConnectivityManager.EXTRA_NO_CONNECTIVITY, false);
        boolean isNetworkConnectedCurrent;

        if (disconnected) {
            isNetworkConnectedCurrent = false;
        } else {
            NetworkInfo networkInfo;

            if (Build.VERSION.SDK_INT < 17) {
                networkInfo = intent.getParcelableExtra(ConnectivityManager.EXTRA_NETWORK_INFO);
            } else {
                ConnectivityManager cm = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);
                int networkType = intent.getIntExtra(ConnectivityManager.EXTRA_NETWORK_TYPE, 0);
                networkInfo = cm.getNetworkInfo(networkType);
            }

            if (networkInfo != null && networkInfo.isConnected()) {
                isNetworkConnectedCurrent = true;
            } else {
                isNetworkConnectedCurrent = false;
            }
        }

        if (isNetworkConnectedCurrent != isNetworkConnected) {
            isNetworkConnected = isNetworkConnectedCurrent;
            Logger.d(TAG, "NetworkStatus.onReceive - isNetworkConnected: " + isNetworkConnected);
            notifyObservers(isNetworkConnected);
        }

 if (isNetworkConnected) {
            // already connected
        } else {
            Utils.showDialog(context, "", context.getString(R.string.default_network_error_message), false,
                    context.getString(R.string.retry), new DialogInterface.OnClickListener() {

                @Override
                public void onClick(DialogInterface dialog, int which) {
                    // handle click action
                }
            });
        }
    }

    /**
     * Lets all {@link NetworkStatusObserver}s know if the device is connected to a network.
     *
     * @param isNetworkConnectedCurrent
     */
    private void notifyObservers(Boolean isNetworkConnectedCurrent) {
        for (NetworkStatusObserver networkStatusObserver : mObserverList) {
            networkStatusObserver.notifyConnectionChange(isNetworkConnectedCurrent);
        }
    }

    public void addObserver(NetworkStatusObserver observer) {
        mObserverList.add(observer);
    }

    public void removeObserver(NetworkStatusObserver observer) {
        mObserverList.remove(observer);
    }

    /**
     * Interface for monitoring network status change
     */
    public interface NetworkStatusObserver {
        void notifyConnectionChange(boolean isConnected);
    }

我在Utils.java中调用的对话框方法是

public static void showDialog(Context context, String title, String message, boolean cancelable, String buttonLabel, DialogInterface.OnClickListener buttonListener) {
    if (isDialogShowing()) {
        return;
    }

    AlertDialog.Builder builder = new AlertDialog.Builder(context);
    builder.setTitle(title)
            .setMessage(message)
            .setCancelable(cancelable)
            .setNeutralButton(buttonLabel, buttonListener);
    mDialog = builder.create();
    mDialog.show(); // <--- the error comes on this line
}

我在清单中注册了这个接收器

<receiver android:name=".network.ConnectionReceiver">
    <intent-filter >
        <action android:name="android.net.wifi.STATE_CHANGE"/>
    </intent-filter>
</receiver>

问题是我将应用程序上下文传递给对话框而不是 Activity 对话框。因此，我删除了广播接收器中调用对话框的代码部分，并尝试将其添加到我的 MainActivity.java class 中。我实现了 NetworkStatusObserver，但在这样做时我收到

的错误

notifyConnectionChange 无法解析

我不确定观察者应该如何发生。顺便说一句，MainActivity extends FragmentActivity 这让我很难在 onPause() 和 onResume() 中 add/remove 我的观察者，因为我不确定用什么来代替"this"。 "this" 应该是什么？

// Note: connectionStatusReceiver is an object of ConnectionReceiver
unregisterReceiver(connectionStatusReceiver );
connectionStatusReceiver.removeObserver(this);

并在我的 onResume() 中尝试添加

connectionStatusReceiver.addObserver(this);
registerReceiver(connectionStatusReceiver , new IntentFilter(ConnectivityManager.CONNECTIVITY_ACTION));

Answer 1

我找到了问题的答案。我无法从我的广播接收器启动对话，因为我将应用程序上下文而不是 Activity 上下文传递给我的对话。解决方案是在我希望监视网络更改的片段和活动上实现 NetworkStatusObserver 接口。在这样做的同时，我必须记住注册和取消注册我的接收器。对于 Activites，我在 onResume()/onPause() 中注册和注销了我的接收器，对于片段，我在 onStart()/onPause() 中注册和注销了我的接收器。

下面是我显示对话框的方式。

@Override
public void notifyConnectionChange(boolean isConnected) {
    Logger.i(TAG, "notifyConnectionChange: " + isConnected);
    if (isConnected && DeviceUtils.isNetworkAvailable(getActivity().getApplicationContext()) &&
            DialogUtils.isDialogShowing()) {
        DialogUtils.dismissDialog();
    } else {
        DialogUtils.showDialog(getActivity().getApplicationContext(), "",
                getString(R.string.default_network_error_message), false,
                getString(R.string.retry), new DialogInterface.OnClickListener() {

                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        if (DeviceUtils.isNetworkAvailable(getActivity().getApplicationContext())) {
                            DialogUtils.dismissDialog();
                        }

                    }
                });
    }
}

希望这能帮助对如何使用观察者模式有类似误解的人。干杯！

Answer 2

在 showDialog()

中传递 YourActivity.this 对象而不是 Context

喜欢

public static void showDialog(Acitivity activity, String title, String message, boolean cancelable, String buttonLabel, DialogInterface.OnClickListener buttonListener) {
    if (isDialogShowing()) {
        return;
    }

    AlertDialog.Builder builder = new AlertDialog.Builder(activity);
    builder.setTitle(title)
            .setMessage(message)
            .setCancelable(cancelable)
            .setNeutralButton(buttonLabel, buttonListener);
    mDialog = builder.create();
    mDialog.show(); // <--- the error comes on this line
}

你可以看到这个Link for Reference:

Android 'Unable to add window — token null is not for an application' 异常

Android 'Unable to add window — token null is not for an application' exception

android

broadcastreceiver

observer-pattern