java - 如何从 C++/Qt 调用 QtActivity 中的非静态 Java 方法

Question

Eskil Abrahamsen Blomfeldt 在他的博客上有一篇文章展示了如何从 C++ 调用 QtActivity/(HangmanActivity) 静态 Java 方法 here .

他提到他只使用静态方法，因为这更容易(确实)并且在他的示例中不需要更多。引用:

In my game, the Activity is a singleton, so I store a static reference to the object in the constructor. (My C++ Data class has the same logic. I’m doing this so that I can facilitate the communication between the Java and the C++ code using static methods. For a more complex example, it’s also possible to store references and pointers in each C++ and Java object that maps it to its equivalent in the other language, but that is not necessary in this game.)

调用静态方法有效。调用非静态方法不起作用(永远不会输入函数)。如果我在 onCreate() 中调用非静态方法 connectBluetooth() 它会起作用。有没有一种方法可以在 onCreate() 中调用而不具有非静态方法？

编辑:

我想我会添加一些代码。我扩展了 QtActivity 类:

package org.qtproject.qt5.android.bindings;

import org.qtproject.qt5.android.bindings.QtApplication;
import org.qtproject.qt5.android.bindings.QtActivity;
import android.bluetooth.BluetoothAdapter;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import java.lang.String;

public class MyActivity extends QtActivity
{
    private BluetoothAdapter bluetoothAdapter;
    private static final int ENABLE_BLUETOOTH_REQUEST = 1;

        public MyActivity()
        {
            Log.d(QtApplication.QtTAG, "MyActivity constructor called");
        }

        @Override
        public void onCreate(Bundle savedInstanceState)
        {
            super.onCreate(savedInstanceState);
        }

        @Override
        public void onDestroy()
        {
            super.onDestroy();
        }

    @Override
        protected void onActivityResult(int requestCode, int resultCode, Intent data)
    {
                Log.d(QtApplication.QtTAG, "onActivityResult entered");
        if(requestCode == 1)
        {
            if(requestCode == 1)
            {
                if(resultCode == RESULT_OK)
                {
                                        Log.d(QtApplication.QtTAG, "User accepted to enable Bluetooth");
                }
                else if(resultCode == RESULT_CANCELED)
                {
                                        Log.d(QtApplication.QtTAG, "User declined to enable Bluetooth");
                }
            }
        }
    }

        public void connectBluetooth()
        {
            Log.d(QtApplication.QtTAG, "connectBluetooth() entered");
            bluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
            if(bluetoothAdapter == null)
            {
                Log.d(QtApplication.QtTAG, "Bluetooth adapter is not found");
                return;
            }

            if(!bluetoothAdapter.isEnabled())
            {
                Log.d(QtApplication.QtTAG, "Bluetooth is off");
                Intent enableBluetoothIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
                startActivityForResult(enableBluetoothIntent, ENABLE_BLUETOOTH_REQUEST);
            }
        }

        public static void test()
        {
            Log.d(QtApplication.QtTAG, "Static Test OK!");
        }
}

然后我尝试从这个 C++ 类中调用这些方法:

#include "bluetooth.h"
#include <QtAndroidExtras>
#include <QDebug>

Bluetooth::Bluetooth(QObject *parent) :
    QObject(parent)
{
}

void Bluetooth::connect()
{
    //Test static call
    QAndroidJniObject::callStaticMethod<void>("org/qtproject/qt5/android/bindings/MyActivity", "test");


    //Test non-static call
    //Line below creates a new object and is a subclass of QtActivity.
    bluetooth = new QAndroidJniObject("org/qtproject/qt5/android/bindings/MyActivity");

    if(!bluetooth->isValid())
    {
        qDebug() << "bluetooth is an invalid java object";
        return;
    }

    bluetooth->callMethod<void>("connectBluetooth");
}

编辑:我最不确定的程序部分是 AndroidManifest.xml。也许这里有什么可以解释这种行为？

<?xml version='1.0' encoding='utf-8'?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android" android:versionCode="1" package="org.qtproject.example.AndroidTest" android:versionName="1.0" android:installLocation="auto">
    <application android:label="@string/app_name" android:name="org.qtproject.qt5.android.bindings.QtApplication">
        <activity android:configChanges="orientation|uiMode|screenLayout|screenSize|smallestScreenSize|locale|fontScale|keyboard|keyboardHidden|navigation" android:label="@string/app_name" android:name="org.qtproject.qt5.android.bindings.MyActivity" android:screenOrientation="unspecified">
            <intent-filter>
                <action android:name="android.intent.action.MAIN"/>
                <category android:name="android.intent.category.LAUNCHER"/>
            </intent-filter>
            <meta-data android:value="AndroidTest" android:name="android.app.lib_name"/>
            <meta-data android:resource="@array/qt_sources" android:name="android.app.qt_sources_resource_id"/>
            <meta-data android:value="default" android:name="android.app.repository"/>
            <meta-data android:resource="@array/qt_libs" android:name="android.app.qt_libs_resource_id"/>
            <meta-data android:resource="@array/bundled_libs" android:name="android.app.bundled_libs_resource_id"/>
            <!-- Deploy Qt libs as part of package -->
            <meta-data android:value="1" android:name="android.app.bundle_local_qt_libs"/>
            <meta-data android:resource="@array/bundled_in_lib" android:name="android.app.bundled_in_lib_resource_id"/>
            <meta-data android:resource="@array/bundled_in_assets" android:name="android.app.bundled_in_assets_resource_id"/>
            <!-- Run with local libs -->
            <meta-data android:value="1" android:name="android.app.use_local_qt_libs"/>
            <meta-data android:value="/data/local/tmp/qt/" android:name="android.app.libs_prefix"/>
            <meta-data android:value="plugins/platforms/android/libqtforandroidGL.so:lib/libQt5QuickParticles.so" android:name="android.app.load_local_libs"/>
            <meta-data android:value="jar/QtAndroid.jar:jar/QtAndroidAccessibility.jar:jar/QtAndroid-bundled.jar:jar/QtAndroidAccessibility-bundled.jar" android:name="android.app.load_local_jars"/>
            <meta-data android:value="" android:name="android.app.static_init_classes"/>
            <!--  Messages maps -->
            <meta-data android:value="@string/ministro_not_found_msg" android:name="android.app.ministro_not_found_msg"/>
            <meta-data android:value="@string/ministro_needed_msg" android:name="android.app.ministro_needed_msg"/>
            <meta-data android:value="@string/fatal_error_msg" android:name="android.app.fatal_error_msg"/>
            <!--  Messages maps -->
            <!-- Splash screen -->
            <meta-data android:resource="@layout/splash" android:name="android.app.splash_screen"/>
            <!-- Splash screen -->
        </activity>
    </application>
    <uses-sdk android:minSdkVersion="14" android:targetSdkVersion="19"/>
    <supports-screens android:smallScreens="true" android:anyDensity="true" android:largeScreens="true" android:normalScreens="true"/>
    <uses-permission android:name="android.permission.BLUETOOTH"/>
    <uses-permission android:name="android.permission.BLUETOOTH_ADMIN"/>
    <uses-permission android:name="android.permission.INTERNET"/>
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
</manifest>

Answer 1

我仍然无法调用非静态函数，但解决方法是使用 singelton pattern它将类的实例化限制为一个对象，并调用能够调用非静态方法的静态函数。

这是通过在构造函数中添加对自身的类/对象引用来完成的:

private static MyActivity m_instance;

public MyActivity()
{
    m_instance = this;
}

现在可以在静态函数中调用非静态函数。例如，上面的非静态函数 bluetoothConnect() 现在可以重写为:

public static void connectBluetooth()
{
    Log.d(QtApplication.QtTAG, "connectBluetooth() entered");
    m_instance.bluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
    if(m_instance.bluetoothAdapter == null)
    {
        Log.d(QtApplication.QtTAG, "Bluetooth adapter is not found");
        return;
    }

    if(!m_instance.bluetoothAdapter.isEnabled())
    {
        Log.d(QtApplication.QtTAG, "Bluetooth is off");
        Intent enableBluetoothIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
        m_instance.startActivityForResult(enableBluetoothIntent, ENABLE_BLUETOOTH_REQUEST);
    }
    else
    {
        Log.d(QtApplication.QtTAG, "Bluetooth is on");
        m_instance.startDiscovery();
    }
}

这里唯一的区别是在方法中添加了 static 关键字并添加了“m_instance”。在每个非静态方法调用之前。

此函数现在可以作为静态函数从 C++ 中调用:

QAndroidJniObject::callStaticMethod<void>("org/qtproject/qt5/android/bindings/MyActivity", "connectBluetooth");

我想这是一个单例的缺点是只能创建此类的一个对象，但据我所知它不会限制太多..

这只是一种解决方法，我仍然对如何调用非静态函数很感兴趣。此答案不会被接受为已接受的答案。