无法从 Qt C++ 调用 Java 函数

Question

任何人都可以帮助解决这个问题吗，我正在为 android 创建一个应用程序，我需要从 Qt C++ 调用 java 函数，我正在使用以下信息进行测试。

请参阅下面的 CMakeLists.txt 文件。

cmake_minimum_required(VERSION 3.16)

project(testing VERSION 0.1 LANGUAGES CXX)

set(CMAKE_CXX_STANDARD_REQUIRED ON)

find_package(Qt6 6.5 REQUIRED COMPONENTS Quick Widgets Core)

qt_standard_project_setup(REQUIRES 6.5)

qt_add_executable(apptesting
    main.cpp
)

qt_add_qml_module(apptesting
    URI testing
    VERSION 1.0
    QML_FILES
        Main.qml
        RESOURCES
            android/AndroidManifest.xml
            android/build.gradle
            android/res/values/libs.xml
            android/res/xml/qtprovider_paths.xml
            android/gradle/wrapper/gradle-wrapper.jar
            android/gradle/wrapper/gradle-wrapper.properties
            android/gradle.properties
            android/gradlew
            android/gradlew.bat
            android/src/org/qtproject/example/file/MathOperations.java

        SOURCES
            mathbridge.h mathbridge.cpp
)


# Set Android source directory
set(android_package_dir "${CMAKE_SOURCE_DIR}/android")

# Qt for iOS sets MACOSX_BUNDLE_GUI_IDENTIFIER automatically since Qt 6.1.
# If you are developing for iOS or macOS you should consider setting an
# explicit, fixed bundle identifier manually though.
set_target_properties(apptesting PROPERTIES
#    MACOSX_BUNDLE_GUI_IDENTIFIER com.example.apptesting
    MACOSX_BUNDLE_BUNDLE_VERSION ${PROJECT_VERSION}
    MACOSX_BUNDLE_SHORT_VERSION_STRING ${PROJECT_VERSION_MAJOR}.${PROJECT_VERSION_MINOR}
    MACOSX_BUNDLE TRUE
    WIN32_EXECUTABLE TRUE
)

target_link_libraries(apptesting
    PRIVATE Qt6::Quick
    PRIVATE Qt6::Widgets
    PRIVATE Qt6::Core
)

include(GNUInstallDirs)
install(TARGETS apptesting
    BUNDLE DESTINATION .
    LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
    RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR}
)

Java 文件

package org.qtproject.example.file;

import android.app.Activity;
import android.widget.Toast;
import org.qtproject.qt.android.QtNative;

public class MathOperations {
    public static String add() {
        return "This is a test for addition";
    }

    public static String multiply() {
        return "This is a test for multiplication";
    }
}

下面是我的Qt C++实现代码

#include "mathbridge.h"
#include <QJniObject>
#include <QDebug>

QString MathBridge::addNumbers() {
    QJniObject result = QJniObject::callStaticObjectMethod(
        "org/qtproject/example/file/MathOperations", // Fully qualified Java class name
        "add",                                             // Java method name
        "()Ljava/lang/String;"                             // JNI method signature
        );

    if (result.isValid()) {
        QString value = result.toString();
        qDebug() << "Addition Result:" << value;
        return value;
    } else {
        qDebug() << "Failed to call add() in Java";
        return "Error";
    }
}

QString MathBridge::multiplyNumbers() {
    QJniObject result = QJniObject::callStaticObjectMethod(
        "org/qtproject/example/file/MathOperations", // Fully qualified Java class name
        "multiply",                                        // Java method name
        "()Ljava/lang/String;"                             // JNI method signature
        );

    if (result.isValid()) {
        QString value = result.toString();
        qDebug() << "Multiplication Result:" << value;
        return value;
    } else {
        qDebug() << "Failed to call multiply() in Java";
        return "Error";
    }
}

我收到错误消息说没有找到类“org.qtproject.example.file.MathOperations”

请查看下面的错误

W libapptesting_x86_64.so: java.lang.ClassNotFoundException: Didn't find class "org.qtproject.example.file.MathOperations" on path: DexPathList[[zip file "/data/app/~~8CDaDhFP1VCP5LeUpwjwoQ==/org.qtproject.example.apptesting-Ltr2ET7MHeEnfYKGtla3Zw==/base.apk"],nativeLibraryDirectories=[/system/lib64, /system_ext/lib64]]
W libapptesting_x86_64.so:  at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:259)
W libapptesting_x86_64.so:  at java.lang.ClassLoader.loadClass(ClassLoader.java:379)
W libapptesting_x86_64.so:  at java.lang.ClassLoader.loadClass(ClassLoader.java:312)
W libapptesting_x86_64.so:  at org.qtproject.qt.android.QtNative.startQtApplication(Native Method)
W libapptesting_x86_64.so:  at org.qtproject.qt.android.QtNative$$ExternalSyntheticLambda4.run(D8$$SyntheticClass:0)
W libapptesting_x86_64.so:  at org.qtproject.qt.android.QtThread$1.run(QtThread.java:25)
W libapptesting_x86_64.so:  at java.lang.Thread.run(Thread.java:1012)
11-25 20:46:31.682 12976 13041 W libapptesting_x86_64.so:
D libapptesting_x86_64.so: Failed to call add() in Java
W libapptesting_x86_64.so: java.lang.ClassNotFoundException: Didn't find class "org.qtproject.example.file.MathOperations" on path: DexPathList[[zip file "/data/app/~~8CDaDhFP1VCP5LeUpwjwoQ==/org.qtproject.example.apptesting-Ltr2ET7MHeEnfYKGtla3Zw==/base.apk"],nativeLibraryDirectories=[/system/lib64, /system_ext/lib64]]
W libapptesting_x86_64.so:  at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:259)
W libapptesting_x86_64.so:  at java.lang.ClassLoader.loadClass(ClassLoader.java:379)
W libapptesting_x86_64.so:  at java.lang.ClassLoader.loadClass(ClassLoader.java:312)
W libapptesting_x86_64.so:  at org.qtproject.qt.android.QtNative.startQtApplication(Native Method)
W libapptesting_x86_64.so:  at org.qtproject.qt.android.QtNative$$ExternalSyntheticLambda4.run(D8$$SyntheticClass:0)
W libapptesting_x86_64.so:  at org.qtproject.qt.android.QtThread$1.run(QtThread.java:25)
W libapptesting_x86_64.so:  at java.lang.Thread.run(Thread.java:1012)
11-25 20:46:31.713 12976 13041 W libapptesting_x86_64.so:
D libapptesting_x86_64.so: Failed to call multiply() in Java

阅读了一些帖子后，我知道 android/src/org/qtproject/example/file/MathOperations.java 目录不应该位于 CMakeLists.txt 中的 RESOURCES 中。

但是我没有将此目录添加到资源中，当我使用 QT Creator 中的“添加现有目录..”将子目录添加到 android 内部时，该子目录会自行添加到资源中。

当我尝试从 CMakeLists.txt 中的资源中删除时，该子目录将从 Qt Creator 中的 android 文件夹中删除，拥有自己的子目录。

有人可以就我的以下疑问提出建议吗？

1. 应该将android/src/org/qtproject/example/file/MathOperations.java添加到QT Creator的android目录中吗？

2. 如果要添加，那么如何避免它被添加到CMakeLists.txt中的RESOURCES中？

3. 如果不应该添加它，那么我如何以及在哪里指定 CMakeLists.txt 或 build.gradle 来编译并添加到 Android 应用程序？

4. 我的CMakeLists.txt是错误的吗，这就是为什么java文件没有被编译并且没有添加到android应用程序中的原因？

我们将非常感谢您的帮助。

谢谢，

Answer 1

答案可以在这里找到：

Java 和 C++

CMakeLists.txt