java - 如何将 android.content.Context 参数(从 native 代码)发送到 Java fct(通过 JNI)

Question

我正在为我的 Android 手机开发一个应用程序，我正在尝试启用 Wifi 热点。我正在使用 Qt 5.4.1，所以我用 C++ 开发。由于在 NDK 中没有任何函数可以执行此操作，因此我使用 JNI 来调用 Java 方法。

我的 java 代码是(感谢 Ashish Sahu 在 stackoverflow thread 中的回答):

package org.app.test;

import android.content.*;
import android.net.wifi.*;
import java.lang.reflect.*;

//Class that handles Wifi Hotspot (access point) configuration
public class ApManager {

    //Is Wifi hotspot on or off ?
    public static boolean isApOn(Context context) {
        WifiManager wifimanager = (WifiManager) context.getSystemService(context.WIFI_SERVICE);
        try {
            Method method = wifimanager.getClass().getDeclaredMethod("isWifiApEnabled");
            method.setAccessible(true);
            return (Boolean) method.invoke(wifimanager);
        }
        catch (Throwable ignored) {}
        return false;
    }

    //Turn Wifi hotspot on or off
    public static boolean configApState(Context context, boolean b) {
        WifiManager wifimanager = (WifiManager) context.getSystemService(context.WIFI_SERVICE);
        WifiConfiguration wificonfiguration = null;
        try {
            //if Wifi is on, turn it off
            if(isApOn(context)) {
                wifimanager.setWifiEnabled(false);
            }
            Method method = wifimanager.getClass().getMethod("setWifiApEnabled", WifiConfiguration.class, boolean.class);
            method.invoke(wifimanager, wificonfiguration, b);
            return true;
        }
        catch(Exception e) {
            e.printStackTrace();
        }
        return false;
    }       
}

C++ 代码示例:

setWifiApEnabled(QAndroidJniObject context, bool b)
{
    return QAndroidJniObject::callStaticMethod<jboolean>("org/app/test/ApManager"
                                                         , "configApState"
                                                         , "(Ljava/lang/Object;Z)Z" //Or (Landroid/content/Context;Z)Z ???
                                                         , context.object<jobject>()
                                                         , b);
}

但是现在我遇到了一个问题；如何获取参数 context 在我调用它时传递给函数 setWifiApEnabled(context, b) ？

我有点迷茫，我读了一些关于这个问题的帖子 (like this one)，但我不完全理解回答者的意思。

你能帮我解决这个问题吗？

编辑:我在这个 stackoverflow thread 上找到了一种获取上下文的方法:

interface = QApplication::platformNativeInterface();
activiti = (jobject)interface->nativeResourceForIntegration("QtActivity");
at = new QAndroidJniObject(activiti);
appctx = at->callObjectMethod("getApplicationContext", "()Landroid/content/Context;");
if(appctx.isValid()) qDebug() << "I am valid !";
else qDebug() << "I ain't valid !";

appctx 有效，但 Wifi 热点未启用，我无法获取其状态。

编辑 2::我成功地使用 Android Studio 在 Java 中启用了 Wifi 热点。代码如下:

WifiApManager.java :

public class WifiApManager {
    private WifiManager wifiMan;
    protected Method setWifiApEnabledMethod, isWifiApEnabledMethod;
    protected final static int MAX_ITER = 10;

    public WifiApManager(WifiManager wifiMan) {
        this.wifiMan = wifiMan;
        getHiddenMethods();
    }

    private void getHiddenMethods() {
        try {
            setWifiApEnabledMethod = wifiMan.getClass().getMethod("setWifiApEnabled", WifiConfiguration.class, boolean.class);
            isWifiApEnabledMethod = wifiMan.getClass().getMethod("isWifiApEnabled");
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
        }
    }

    public boolean isWifiApEnabled() {
        try {
            return (Boolean)isWifiApEnabledMethod.invoke(wifiMan);
        } catch (Exception e) {
            return false;
        }
    }

    public boolean isWifiEnabled() {
        return wifiMan.isWifiEnabled();
    }

    public boolean setWifiApEnabled(WifiConfiguration conf, boolean enabled) {
        try {
            return (Boolean) setWifiApEnabledMethod.invoke(wifiMan, conf, true);
        } catch (Exception e) {
            return false;
        }
    }

    public boolean toggleWifi(String ssid) {
        // WifiConfiguration creation:
        WifiConfiguration conf = new WifiConfiguration();
        conf.SSID = ssid;
        conf.allowedAuthAlgorithms.set(WifiConfiguration.AuthAlgorithm.OPEN);

        // If AP Wifi is enabled, disables it and returns:
        if(isWifiApEnabled()) {
            //setWifiApEnabled(null, false); Won't work, see two further lines
            wifiMan.setWifiEnabled(true);
            wifiMan.setWifiEnabled(false);
            int maxIter = MAX_ITER;
            while (isWifiApEnabled() && maxIter-- >= 0) {
                try {Thread.sleep(500);} catch (Exception e) {}
            }
            return isWifiApEnabled();
        }

        // If standard Wifi is enabled, disables it:
        if (isWifiEnabled()) {
            if (wifiMan.setWifiEnabled(false)) {
                int maxIter = MAX_ITER;
                while (wifiMan.isWifiEnabled() && maxIter-- >= 0) {
                    try {Thread.sleep(500);} catch (Exception e) {}
                }
            }
            if (isWifiEnabled()) {
                return false;
            }
        }

        // Enables AP Wifi
        try {
            if (! setWifiApEnabled(conf, true)) {
                System.out.println("setWifiApEnabledMethod failed.");
                return false;
            }
            int maxIter = MAX_ITER;
            while (! isWifiApEnabled() && maxIter-- > 0) {
                try {Thread.sleep(500);} catch (Exception e) {}
            }
        } catch(Exception e) {
            e.printStackTrace();
            return false;
        }
        return true;
    }
}

主类:

public class AndroidMenusActivity extends Activity implements OnClickListener {
    private WifiApManager wifiMan;
    private ToggleButton wifiButton;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        wifiMan = new WifiApManager((WifiManager) this.getSystemService(Context.WIFI_SERVICE));
        setContentView(R.layout.activity_android_menus);
        makeUI();
    }

    private void makeUI() {
        LinearLayout subLayout = (LinearLayout) findViewById(R.id.subLayout);
        wifiButton = new ToggleButton(this);
        wifiButton.setTextOn("Disable Wifi");
        wifiButton.setTextOff("Enable AP Wifi");
        wifiButton.setChecked(wifiMan.isWifiApEnabled());
        wifiButton.setOnClickListener(this);
        subLayout.addView(wifiButton);
    }

    @Override
    public void onClick(View sender) {
        if (!wifiButton.equals(sender))
            return;

        AsyncTask<Object, Void, Boolean> task = new AsyncTask<Object, Void, Boolean>() {
            private ToggleButton bt;
            private WifiApManager wm;

            @Override
            protected Boolean doInBackground(Object... args) {
                bt = (ToggleButton) args[0];
                wm = (WifiApManager) args[1];
                return wm.toggleWifi("test.com");
            }
            @Override
            protected void onPostExecute (Boolean result) {
                bt.setChecked(result.booleanValue());
                bt.setEnabled(true);
            }
        };
        wifiButton.setEnabled(false);
        task.execute(wifiButton, wifiMan);
    }
}

但是我找不到在 C++ 中做同样事情的方法，有什么帮助吗？

Answer 1

只是为了将上下文对象从 C++ 传输到 JNI，使用这样的自动注入(inject):

QtAndroid::androidActivity().callStaticMethod<void>(
      "com/company/project/MyApp",
      "myFunc", // method name
      "(Landroid/content/Context;)V" // auto-injection
    );