Android VpnService.Builder.establish() 偶尔为空

Question

当我尝试为我的 VpnService 创建隧道接口(interface)时，出现以下错误:

Attempt to invoke virtual method 'java.lang.String android.os.ParcelFileDescriptor.toString()' on a null object reference

我目前唯一的解决办法是在发生这种情况时重启设备。否则，我根本无法创建隧道。

我创建隧道的代码:

// This is inside my VpnService implementation 

private ParcelFileDescriptor configureTunnelWithPushOpts(PushOpts popts)
{
    VpnService.Builder builder = this.new Builder();

    builder.setMtu       ( currentServerPrefs.SERVER_MTU );
    builder.addAddress   ( popts.ip, 32                  );
    builder.addDnsServer ( popts.dns1                    );
    builder.addDnsServer ( popts.dns2                    );
    builder.addRoute     ( "0.0.0.0", 0                  );


    // Note: Blocking mode is now enabled in native
    // code under the setFileDescriptor function.
    // builder.setBlocking(true);

    builder.setConfigureIntent(
            PendingIntent.getActivity(
                    this,
                    0,
                    new Intent(
                            this,
                            MainActivity.class
                    ),
            PendingIntent.FLAG_UPDATE_CURRENT)
    );

    final ParcelFileDescriptor vpnInterface;

    synchronized (this) {
        builder.setSession(currentServerPrefs.SERVER_ADDRESS);
        vpnInterface = builder.establish();
    }

    Logger.info("New interface: " + vpnInterface.toString(), this);
    return vpnInterface;
}

编辑:

根据文档，如果 VpnService 尚未准备好，establish 函数将返回 null，但是我在运行上述函数之前使用它来准备它.

// This is inside my MainActivity class

Intent intent = VpnService.prepare(getApplicationContext());
if (intent != null) {
    startActivityForResult(intent, 0);
} else {
    onActivityResult(0, RESULT_OK, null);
}

. . . 

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    if (resultCode == RESULT_OK) {
        Intent intent = new Intent(this, MyVpnService.class);
        startService(intent);
    }
}

我用来调试的手机

运行 Android 5.0.1 的 Google Nexus 5

Edit

I figured out how to replicate it so that it's no longer sporadic. Basically, if I uninstall the application while the VPN is connected, and then reinstall it and try to start it back up, I receive a null response when i run builder.establish(). I fear this could pose potential issues when the application is updated through the Google Play Store.

Aside from that, Please do not mark this question as a duplicate. Every other question on this matter has been given the answer that the service needs to be prepared before the builder is established, however I am preparing it in my case and have a different cause for my problem. Any help would be appreciated.

Answer 1

非常感谢您的提示，它让我找到了解决方案!

我在 Android 5.0.2 中遇到了同样的问题:一切正常，我安装了我正在开发的 vpn 应用程序。第二天，尽管正确调用了 prepare，但突然出现无法解析的 NullPointerException。

可以通过以下步骤在我的环境中解决该问题:

• 卸载应用程序。应用程序是否仍具有 VPN 功能并不重要。
• 重启手机。确保它已完全关闭。
• 重启后，确保不再安装该应用程序(我遇到了一些奇怪的开发问题，即在我的手机重启后重新安装了一个应用程序)。
• 重新安装您的 VPN 应用。它现在应该接收一个 vpn 接口(interface)，而不是 null。