无法使用QAndroidJniObject与Java类合并

Question

我需要在我的Qt中为Android项目使用Java库和函数，所以我已经开始很简单了。

这是我现在的AESCrypt.java

package org.qcolocrypt;
public class AESCrypt extends org.qtproject.qt5.android.bindings.QtActivity{
   public static String getTestString() { return "This is a Test String"; }
}

现在，我的Qt项目驻留在Apps/QColoCrypt以及我的cpp和h文件中。在该目录中，我有以下结构：

Apps/QColoCrypt/java/AndroidManifest.xml
Apps/QColoCrypt/java/src/org/qcolocrypt/AESCrypt.java

我的.pro文件如下所示：

#-------------------------------------------------
#
# Project created by QtCreator 2017-11-23T06:31:24
#
#-------------------------------------------------

QT       += core gui androidextras

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

TARGET = QColoCrypt
TEMPLATE = app

ANDROID_PACKAGE_SOURCE_DIR = $$PWD/java

SOURCES += main.cpp\
        mainview.cpp

HEADERS  += mainview.h

FORMS    += mainview.ui

MOC_DIR = MOCS
OBJECTS_DIR = OBJS

CONFIG += mobility
MOBILITY = 

OTHER_FILES += \
    java/AndroidManifest.xml \
    java/src/org/qcolocrypt/AESCrypt.java

以防我的AndroidManifest看起来像这样：

<?xml version="1.0"?>
<manifest package="org.qtproject.example.QColoCrypt" xmlns:android="http://schemas.android.com/apk/res/android" android:versionName="1.0" android:versionCode="1" android:installLocation="auto">
    <application android:hardwareAccelerated="true" android:name="org.qtproject.qt5.android.bindings.QtApplication" android:label="QColoCrypt">
        <activity android:configChanges="orientation|uiMode|screenLayout|screenSize|smallestScreenSize|layoutDirection|locale|fontScale|keyboard|keyboardHidden|navigation" android:name="org.qtproject.qt5.android.bindings.QtActivity" android:label="QColoCrypt" android:screenOrientation="unspecified" android:launchMode="singleTop">
            <intent-filter>
                <action android:name="android.intent.action.MAIN"/>
                <category android:name="android.intent.category.LAUNCHER"/>
            </intent-filter>

            <!-- Application arguments -->
            <!-- meta-data android:name="android.app.arguments" android:value="arg1 arg2 arg3"/ -->
            <!-- Application arguments -->

            <meta-data android:name="android.app.lib_name" android:value="QColoCrypt"/>
            <meta-data android:name="android.app.qt_sources_resource_id" android:resource="@array/qt_sources"/>
            <meta-data android:name="android.app.repository" android:value="default"/>
            <meta-data android:name="android.app.qt_libs_resource_id" android:resource="@array/qt_libs"/>
            <meta-data android:name="android.app.bundled_libs_resource_id" android:resource="@array/bundled_libs"/>
            <!-- Deploy Qt libs as part of package -->
            <meta-data android:name="android.app.bundle_local_qt_libs" android:value="1"/>
            <meta-data android:name="android.app.bundled_in_lib_resource_id" android:resource="@array/bundled_in_lib"/>
            <meta-data android:name="android.app.bundled_in_assets_resource_id" android:resource="@array/bundled_in_assets"/>
            <!-- Run with local libs -->
            <meta-data android:name="android.app.use_local_qt_libs" android:value="1"/>
            <meta-data android:name="android.app.libs_prefix" android:value="/data/local/tmp/qt/"/>
            <meta-data android:name="android.app.load_local_libs" android:value="plugins/platforms/android/libqtforandroid.so"/>
            <meta-data android:name="android.app.load_local_jars" android:value="jar/QtAndroid.jar:jar/QtAndroid-bundled.jar"/>
            <meta-data android:name="android.app.static_init_classes" android:value=""/>
            <!--  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:name="android.app.splash_screen_drawable" android:resource="@drawable/logo"/ -->
            <!-- meta-data android:name="android.app.splash_screen_sticky" android:value="true"/ -->
            <!-- Splash screen -->

            <!-- Background running -->
            <!-- Warning: changing this value to true may cause unexpected crashes if the
                          application still try to draw after
                          "applicationStateChanged(Qt::ApplicationSuspended)"
                          signal is sent! -->
            <meta-data android:name="android.app.background_running" android:value="false"/>
            <!-- Background running -->

            <!-- auto screen scale factor -->
            <meta-data android:name="android.app.auto_screen_scale_factor" android:value="false"/>
            <!-- auto screen scale factor -->

            <!-- extract android style -->
            <!-- available android:values :
                * full - useful QWidget & Quick Controls 1 apps
                * minimal - useful for Quick Controls 2 apps, it is much faster than "full"
                * none - useful for apps that don't use any of the above Qt modules
                -->
            <meta-data android:name="android.app.extract_android_style" android:value="full"/>
            <!-- extract android style -->
    </activity>

    <!-- For adding service(s) please check: https://wiki.qt.io/AndroidServices -->

    </application>

    <uses-sdk android:minSdkVersion="16" android:targetSdkVersion="16"/>
    <supports-screens android:largeScreens="true" android:normalScreens="true" android:anyDensity="true" android:smallScreens="true"/>

    <!-- The following comment will be replaced upon deployment with default permissions based on the dependencies of the application.
         Remove the comment if you do not require these default permissions. -->
        <uses-permission android:name="android.permission.INTERNET"/>
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>


    <!-- The following comment will be replaced upon deployment with default features based on the dependencies of the application.
         Remove the comment if you do not require these default features. -->


</manifest>

编译项目时，生成的所有内容都会进入目录。应用程序/00AndroidBuilds/QColoCrypt

最后，在我的mainview.cpp (只有cpp文件，Qt的main.cpp除外)中，我在一个按钮单击下面的代码：

void MainView::on_pushButton_clicked()
{

    QAndroidJniObject test = QAndroidJniObject::callStaticObjectMethod("org/qcolocrypt/AESCrypt",
                                                                       "getTestString",
                                                                       "(V)Ljava/lang/String;");



    ui->pteLog->appendPlainText("==========TEST STRING================");
    ui->pteLog->appendPlainText(test.toString());

}

据我所知，当一切正常工作时，我应该打印“这是一个测试字符串”。但是，test.toString()函数似乎返回一个空字符串。

所以，要么是编译错误(这就是为什么我添加了所有我认为有针对性的路径信息)，要么是我不正确地调用函数，而我不知道自己做错了什么。

目前使用QT5.7.0，以防万一这很重要。

Answer 1

由于您正在调用不接受参数的Java函数，因此签名应该是：

"()Ljava/lang/String;"

V for void仅用于当函数不返回任何内容时。