使用Qt / C ++通过JNI调用Java代码。 FindClass没有找到类 [英] Using Qt/C++ to call Java code through JNI. FindClass does not find class
本文介绍了使用Qt / C ++通过JNI调用Java代码。 FindClass没有找到类的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我是JNI的新手，这是我第一个尝试从C ++调用Java代码的程序。我正在使用Qt 5.2而且我正在编写一个Android应用程序。
I am new to JNI and this is my first program trying to call Java code from C++. I am using Qt 5.2 and I am writing an Android application.
我无法找到我的java类并将其加载到我的C ++程序中。我已经在堆栈溢出和其他地方阅读了很多帖子，这似乎是一个常见的问题，但我还没能解决我的问题..
I am not able to find my java class and load it into my C++ program. I have read a lot of posts here on stack overflow and other places and it seems to be a common problem, but I have not been able to solve mine yet..
我也不确定Java VM是否已正确设置，因为QAndroidJniEnvironment上的Qt文档很少。
I am also not sure if the Java VM is properly set up as the Qt documentation on the QAndroidJniEnvironment is minimal.
我正在寻找一个如何能够解决方案找到我的java类。我也很感谢代码其他部分的一般反馈（我假设可能会有更多错误）。
I am looking for a solution on how to be able to find my java class. I am also appreciating general feedback on other sections of the code (I assume there might be more errors).
错误消息：
Starting remote process.D/dalvikvm(24911): GC_CONCURRENT freed 384K, 5% free 9180K/9596K, paused 1ms+2ms, total 15ms
D/dalvikvm(24911): Trying to load lib /data/data/org.qtproject.example.AndroidTest/lib/libgnustl_shared.so 0x428b2360
D/dalvikvm(24911): Added shared lib /data/data/org.qtproject.example.AndroidTest/lib/libgnustl_shared.so 0x428b2360
D/dalvikvm(24911): No JNI_OnLoad found in /data/data/org.qtproject.example.AndroidTest/lib/libgnustl_shared.so 0x428b2360, skipping init
D/dalvikvm(24911): Trying to load lib /data/data/org.qtproject.example.AndroidTest/lib/libQt5Core.so 0x428b2360
D/dalvikvm(24911): Added shared lib /data/data/org.qtproject.example.AndroidTest/lib/libQt5Core.so 0x428b2360
D/dalvikvm(24911): Trying to load lib /data/data/org.qtproject.example.AndroidTest/lib/libQt5Network.so 0x428b2360
D/dalvikvm(24911): Added shared lib /data/data/org.qtproject.example.AndroidTest/lib/libQt5Network.so 0x428b2360
I/Qt (24911): Network start
D/dalvikvm(24911): Trying to load lib /data/data/org.qtproject.example.AndroidTest/lib/libQt5Qml.so 0x428b2360
D/dalvikvm(24911): Added shared lib /data/data/org.qtproject.example.AndroidTest/lib/libQt5Qml.so 0x428b2360
D/dalvikvm(24911): No JNI_OnLoad found in /data/data/org.qtproject.example.AndroidTest/lib/libQt5Qml.so 0x428b2360, skipping init
D/dalvikvm(24911): Trying to load lib /data/data/org.qtproject.example.AndroidTest/lib/libQt5Gui.so 0x428b2360
D/dalvikvm(24911): Added shared lib /data/data/org.qtproject.example.AndroidTest/lib/libQt5Gui.so 0x428b2360
D/dalvikvm(24911): No JNI_OnLoad found in /data/data/org.qtproject.example.AndroidTest/lib/libQt5Gui.so 0x428b2360, skipping init
D/dalvikvm(24911): Trying to load lib /data/data/org.qtproject.example.AndroidTest/lib/libQt5Quick.so 0x428b2360
D/dalvikvm(24911): Added shared lib /data/data/org.qtproject.example.AndroidTest/lib/libQt5Quick.so 0x428b2360
D/dalvikvm(24911): No JNI_OnLoad found in /data/data/org.qtproject.example.AndroidTest/lib/libQt5Quick.so 0x428b2360, skipping init
D/dalvikvm(24911): Trying to load lib /data/data/org.qtproject.example.AndroidTest/lib/libQt5QuickParticles.so 0x428b2360
D/dalvikvm(24911): Added shared lib /data/data/org.qtproject.example.AndroidTest/lib/libQt5QuickParticles.so 0x428b2360
D/dalvikvm(24911): No JNI_OnLoad found in /data/data/org.qtproject.example.AndroidTest/lib/libQt5QuickParticles.so 0x428b2360, skipping init
D/dalvikvm(24911): Trying to load lib /data/data/org.qtproject.example.AndroidTest/lib/libQt5AndroidExtras.so 0x428b2360
D/dalvikvm(24911): Added shared lib /data/data/org.qtproject.example.AndroidTest/lib/libQt5AndroidExtras.so 0x428b2360
D/dalvikvm(24911): No JNI_OnLoad found in /data/data/org.qtproject.example.AndroidTest/lib/libQt5AndroidExtras.so 0x428b2360, skipping init
D/dalvikvm(24911): Trying to load lib /data/data/org.qtproject.example.AndroidTest/plugins/platforms/android/libqtforandroidGL.so 0x428b2360
D/dalvikvm(24911): Added shared lib /data/data/org.qtproject.example.AndroidTest/plugins/platforms/android/libqtforandroidGL.so 0x428b2360
I/Qt (24911): qt start
W/dalvikvm(24911): dvmFindClassByName rejecting 'org/qtproject/qt5/android/QtMessageDialogHelper'
D/dalvikvm(24911): Trying to load lib /data/data/org.qtproject.example.AndroidTest/lib/libQt5QuickParticles.so 0x428b2360
D/dalvikvm(24911): Shared lib '/data/data/org.qtproject.example.AndroidTest/lib/libQt5QuickParticles.so' already loaded in same CL 0x428b2360
D/dalvikvm(24911): Trying to load lib /data/app-lib/org.qtproject.example.AndroidTest-1/libAndroidTest.so 0x428b2360
D/Qt (24911): qml\qqmlengine.cpp:1451 (QQmlDebuggingEnabler::QQmlDebuggingEnabler(bool)): QML debugging is enabled. Only use this in a safe environment.
D/dalvikvm(24911): Added shared lib /data/app-lib/org.qtproject.example.AndroidTest-1/libAndroidTest.so 0x428b2360
D/dalvikvm(24911): No JNI_OnLoad found in /data/app-lib/org.qtproject.example.AndroidTest-1/libAndroidTest.so 0x428b2360, skipping init
W/Qt (24911): kernel\qcoreapplication.cpp:416 (QCoreApplicationPrivate::QCoreApplicationPrivate(int&, char**, uint)): WARNING: QApplication was not created in the main() thread.
W/dalvikvm(24911): dvmFindClassByName rejecting 'org/qtproject/qt5/android/QtNativeInputConnection'
W/dalvikvm(24911): dvmFindClassByName rejecting 'org/qtproject/qt5/android/QtExtractedText'
I/Adreno-EGL(24911): <qeglDrvAPI_eglInitialize:320>: EGL 1.4 QUALCOMM Build: I0404c4692afb8623f95c43aeb6d5e13ed4b30ddbDate: 11/06/13
D/Qt (24911): fontdatabases\basic\qbasicfontdatabase.cpp:246 (static QStringList QBasicFontDatabase::addTTFile(const QByteArray&, const QByteArray&)): FT_New_Face failed with index 0 : 90
D/Qt (24911): ..\AndroidTest\jnimathcppwrapper.cpp:18 (jniMathCppWrapper::jniMathCppWrapper()): JniMath class not found
D/Qt (24911): ..\AndroidTest\jnimathcppwrapper.cpp:43 (int jniMathCppWrapper::eleven()): Enter eleven
F/libc (24911): Fatal signal 11 (SIGSEGV) at 0x0000002c (code=1), thread 24933 (ple.AndroidTest)
Java类：
package org.app.test;
public class JniMath {
public JniMath()
{
}
public int eleven()
{
return 11;
}
}
.pro文件：
# Add more folders to ship with the application, here
folder_01.source = qml/AndroidTest
folder_01.target = qml
DEPLOYMENTFOLDERS = folder_01
# Additional import path used to resolve QML modules in Creator's code model
QML_IMPORT_PATH =
# The .cpp file which was generated for your project. Feel free to hack it.
SOURCES += main.cpp #\
# jnimathcppwrapper.cpp
# Installation path
# target.path =
# Please do not modify the following two lines. Required for deployment.
include(qtquick2applicationviewer/qtquick2applicationviewer.pri)
qtcAddDeployment()
RESOURCES += \
resources.qrc
QT += androidextras
OTHER_FILES += \
android/src/org/app/test/JniMath.java
HEADERS += #\
# jnimathcppwrapper.h
android {
SOURCES += jnimathcppwrapper.cpp
HEADERS += jnimathcppwrapper.h
}
main.cpp：
#include <QtGui/QGuiApplication>
#include "qtquick2applicationviewer.h"
#include "jnimathcppwrapper.h"
#include <QDebug>
#include <QString>
int main(int argc, char *argv[])
{
QGuiApplication app(argc, argv);
QtQuick2ApplicationViewer viewer;
viewer.setMainQmlFile(QStringLiteral("qml/AndroidTest/main.qml"));
viewer.showExpanded();
jniMathCppWrapper *test = new jniMathCppWrapper();
qDebug() << QString::number(test->eleven());
return app.exec();
}
jnimathcppwrapper.h：
#ifndef JNIMATHCPPWRAPPER_H
#define JNIMATHCPPWRAPPER_H
#include <QtAndroidExtras>
class jniMathCppWrapper
{
public:
jniMathCppWrapper();
int eleven();
private:
jobject jniMathObject;
};
#endif // JNIMATHCPPWRAPPER_H
jnimathcppwrapper.cpp：
#include "jnimathcppwrapper.h"
#include <QtAndroidExtras>
#include <QDebug>
#include <jni.h>
static jclass jniMathClassID = 0;
static jmethodID jniMathConstructorMethodID = 0;
static jmethodID jniMathElevenMethodID = 0;
jniMathCppWrapper::jniMathCppWrapper()
{
QAndroidJniEnvironment qjniEnv;
//Get JniMath class ID.
jniMathClassID = qjniEnv->FindClass("android/src/org/app/test/JniMath");
if(jniMathClassID == NULL)
{
qDebug() << "JniMath class not found";
return;
}
//Get constructor method ID
jniMathConstructorMethodID = qjniEnv->GetMethodID(jniMathClassID, "<init>", "void(V)");
if(jniMathConstructorMethodID == NULL)
{
qDebug() << "JniMath constructor not found";
return;
}
//Create new Java object and calling the selected constructor.
jniMathObject = qjniEnv->NewObject(jniMathClassID, jniMathConstructorMethodID);
if(jniMathObject == NULL)
{
qDebug() << "JniMath Java object could not be constructed";
return;
}
}
int jniMathCppWrapper::eleven()
{
QAndroidJniEnvironment qjniEnv;
qDebug() << "Enter eleven";
//Get eleven method ID
jniMathElevenMethodID = qjniEnv->GetMethodID(jniMathClassID, "eleven", "void(V)");
if(jniMathElevenMethodID == NULL)
{
qDebug() << "JniMath class, eleven method not found";
return 9;
}
jint res = qjniEnv->CallIntMethod(jniMathObject, jniMathElevenMethodID);
return (int) res;
}
项目结构：
编辑：
我也尝试了一种不同的方法导致同样的错误：
I also tried a different approach leading to the same error:
QAndroidJniObject *myJavaClass = new QAndroidJniObject("android/src/org/app/test/JniMath");
if(myJavaClass->isValid())
{
qDebug() << "Class found!";
}
else
{
qDebug() << "Class NOT found!";
}
当尝试加载java / lang / String时，上述两种方法都会找到分类。
When trying to load java/lang/String instead, both methods above find the class.
编辑：
错误日志：
D/Qt ( 3385): qml\qqmlengine.cpp:1451 (QQmlDebuggingEnabler::QQmlDebuggingEnabler(bool)): QML debugging is enabled. Only use this in a safe environment.
D/dalvikvm( 3385): Added shared lib /data/app-lib/org.qtproject.example.AndroidTest-1/libAndroidTest.so 0x428b67f8
D/Qt ( 3385): ..\AndroidTest\jnimathcppwrapper.cpp:68 (jint JNI_OnLoad(JavaVM*, void*)): Class NOT found
D/AndroidRuntime( 3385): Shutting down VM
W/dalvikvm( 3385): threadid=1: thread exiting with uncaught exception (group=0x41fecba8)
E/AndroidRuntime( 3385): FATAL EXCEPTION: main
E/AndroidRuntime( 3385): Process: org.qtproject.example.AndroidTest, PID: 3385
E/AndroidRuntime( 3385): java.lang.NoClassDefFoundError: org/app/test/JniMath
E/AndroidRuntime( 3385): at java.lang.Runtime.nativeLoad(Native Method)
E/AndroidRuntime( 3385): at java.lang.Runtime.doLoad(Runtime.java:421)
E/AndroidRuntime( 3385): at java.lang.Runtime.loadLibrary(Runtime.java:362)
E/AndroidRuntime( 3385): at java.lang.System.loadLibrary(System.java:526)
E/AndroidRuntime( 3385): at org.qtproject.qt5.android.bindings.QtActivity.loadApplication(QtActivity.java:235)
E/AndroidRuntime( 3385): at org.qtproject.qt5.android.bindings.QtActivity.startApp(QtActivity.java:522)
E/AndroidRuntime( 3385): at org.qtproject.qt5.android.bindings.QtActivity.onCreate(QtActivity.java:744)
E/AndroidRuntime( 3385): at android.app.Activity.performCreate(Activity.java:5231)
W/dalvikvm( 3385): threadid=1: thread exiting with uncaught exception (group=0x41fecba8)
E/AndroidRuntime( 3385): FATAL EXCEPTION: main
E/AndroidRuntime( 3385): Process: org.qtproject.example.AndroidTest, PID: 3385
E/AndroidRuntime( 3385): java.lang.NoClassDefFoundError: org/app/test/JniMath
E/AndroidRuntime( 3385): at java.lang.Runtime.nativeLoad(Native Method)
E/AndroidRuntime( 3385): at java.lang.Runtime.doLoad(Runtime.java:421)
E/AndroidRuntime( 3385): at java.lang.Runtime.loadLibrary(Runtime.java:362)
E/AndroidRuntime( 3385): at java.lang.System.loadLibrary(System.java:526)
E/AndroidRuntime( 3385): at org.qtproject.qt5.android.bindings.QtActivity.loadApplication(QtActivity.java:235)
E/AndroidRuntime( 3385): at org.qtproject.qt5.android.bindings.QtActivity.startApp(QtActivity.java:522)
E/AndroidRuntime( 3385): at org.qtproject.qt5.android.bindings.QtActivity.onCreate(QtActivity.java:744)
E/AndroidRuntime( 3385): at android.app.Activity.performCreate(Activity.java:5231)
E/AndroidRuntime( 3385): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
E/AndroidRuntime( 3385): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
E/AndroidRuntime( 3385): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
E/AndroidRuntime( 3385): at android.app.ActivityThread.access$800(ActivityThread.java:135)
E/AndroidRuntime( 3385): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
E/AndroidRuntime( 3385): at android.os.Handler.dispatchMessage(Handler.java:102)
E/AndroidRuntime( 3385): at android.os.Looper.loop(Looper.java:136)
E/AndroidRuntime( 3385): at android.app.ActivityThread.main(ActivityThread.java:5017)
E/AndroidRuntime( 3385): at java.lang.reflect.Method.invokeNative(Native Method)
E/AndroidRuntime( 3385): at java.lang.reflect.Method.invoke(Method.java:515)
E/AndroidRuntime( 3385): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
E/AndroidRuntime( 3385): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
E/AndroidRuntime( 3385): at dalvik.system.NativeStart.main(Native Method)
E/AndroidRuntime( 3385): Caused by: java.lang.ClassNotFoundException: Didn't find class "org.app.test.JniMath" on path: DexPathList[[zip file "/data/app/org.qtproject.example.AndroidTest-1.apk"],nativeLibraryDirectories=[/data/app-lib/org.qtproject.example.AndroidTest-1, /vendor/lib, /system/lib]]
E/AndroidRuntime( 3385): at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:56)
E/AndroidRuntime( 3385): at java.lang.ClassLoader.loadClass(ClassLoader.java:497)
E/AndroidRuntime( 3385): at java.lang.ClassLoader.loadClass(ClassLoader.java:457)
E/AndroidRuntime( 3385): ... 21 more
评论：为什么这个问题不是重复的（由Alex Cohn提供）
毫无疑问，这里的根本问题与 来自Android JNI中任何线程的FindClass ，但这里提出的问题是一个非常不同的问题，IMO。 作者并未寻找从本机线程访问ClassLoader的通用方法。他（或她）正在寻找一种简单有效的方法来从基于Qt的本机代码访问Java回调。因此，所有关于类加载器如何在Android中工作以及如何修补它的讨论都与他无关。 如果作者另有想法，我很乐意同意将此问题视为重复
Comment: why this question is not a duplicate (by Alex Cohn)
There is no doubt that the root problem here is the same as in FindClass from any thread in Android JNI, but the question asked here is a very different question, IMO. The author was not looking for a generic way to access the ClassLoader from native threads. He (or she) was looking for an easy and efficient way to access a Java callback from Qt-based native code. Therefore all discussion of how class loader works in Android and how this can be patched is irrelevant for him. If the author thinks otherwise, I will gladly agree to close this question as duplicate
请考虑之前的评论无效。这个问题与多线程无关。这是关于如何设置Android Qt应用程序以便它可以使用自定义Java类，类似于示例。
Please consider the previous comment void. This question has nothing to do with multithreading. It's all about how to set up an Android Qt application such that it could use custom Java classes, similar to the sample.
推荐答案
这就是我的做法。
在我的java主类中，我添加了一个静态方法来调用相同的活动（因为它必须是静态的）：
This is how I did it. In my java main class I added a static method to call the same activity (because it has to be static):
static public void startFacebookActivity() {
String msgTag = "FACEBOOK_APP";
try {
Log.v(msgTag, "starting activity");
Activity mother = QtNative.activity();
Log.v(msgTag, mother.toString());
Log.v(msgTag, MainActivity.class.getName());
Intent intent = new Intent(mother, MainActivity.class);
mother.startActivity(intent);
} catch (Exception e) {
Log.e(msgTag, e.toString());
e.printStackTrace();
}
}
然后在我的头文件中我添加了这个：
Then in my header file I added this:
class FacebookAndroid : public QObject {
Q_OBJECT
public:
FacebookAndroid(QObject *parent = 0);
public slots:
void startAndroidFacebook();
};
在我的cpp文件中我刚刚调用了我的java方法：
and In my cpp file I just called my java method like this:
void FacebookAndroid::startAndroidFacebook() {
QAndroidJniObject::callStaticMethod<void>("org.qtproject.example.MainActivity",
"startFacebookActivity",
"()V");
这篇关于使用Qt / C ++通过JNI调用Java代码。 FindClass没有找到类的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
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