QJniEnvironment 类

QJniEnvironment 类提供对 JNIEnv (JNI 环境) 的访问。更多...

头：	#include <QJniEnvironment>
CMake:	find_package(Qt6 REQUIRED COMPONENTS Core) target_link_libraries(mytarget PRIVATE Qt6::Core)
qmake:	QT += core
Since:	Qt 6.1

公共类型

enum class

OutputMode { Silent, Verbose }

公共函数

	QJniEnvironment ()
	~QJniEnvironment ()
bool	checkAndClearExceptions (QJniEnvironment::OutputMode outputMode = OutputMode::Verbose)
jclass	findClass (const char * className )
jfieldID	findField (jclass clazz , const char * fieldName , const char * signature )
jfieldID	findField (jclass clazz , const char * fieldName )
jmethodID	findMethod (jclass clazz , const char * methodName , const char * signature )
jmethodID	findMethod (jclass clazz , const char * methodName )
jfieldID	findStaticField (jclass clazz , const char * fieldName , const char * signature )
jfieldID	findStaticField (jclass clazz , const char * fieldName )
jmethodID	findStaticMethod (jclass clazz , const char * methodName , const char * signature )
jmethodID	findStaticMethod (jclass clazz , const char * methodName )
bool	isValid () const
JNIEnv *	jniEnv () const
bool	registerNativeMethods (const char * className , const JNINativeMethod [] methods , int size )
bool	registerNativeMethods (jclass clazz , const JNINativeMethod [] methods , int size )
JNIEnv &	operator* () const
JNIEnv *	operator-> () const

静态公共成员

bool	checkAndClearExceptions (JNIEnv * env , QJniEnvironment::OutputMode outputMode = OutputMode::Verbose)
JavaVM *	javaVM ()

详细描述

当使用 JNI 时， JNIEnv class is a pointer to a function table and a member function for each JNI function that indirects through the table. JNIEnv provides most of the JNI functions. Every C++ native function receives a JNIEnv as the first argument. The JNI environment cannot be shared between threads.

由于 JNIEnv doesn't do much error checking, such as exception checking and clearing, QJniEnvironment allows you to do that easily.

JNIEnv 的更多有关信息，见 Java：接口功能表 .

注意： This API has been designed and tested for use with Android. It has not been tested for other platforms.

成员类型文档编制

enum class QJniEnvironment:: OutputMode

常量	值	描述
`QJniEnvironment::OutputMode::Silent`	`0`	The exceptions are cleaned silently
`QJniEnvironment::OutputMode::Verbose`	`1`	Prints the exceptions and their stack backtrace as an error to `stderr` stream.

成员函数文档编制

QJniEnvironment:: QJniEnvironment ()

Constructs a new JNI Environment object and attaches the current thread to the Java VM.

QJniEnvironment:: ~QJniEnvironment ()

分离当前线程从 Java VM 和销毁 QJniEnvironment object. This will clear any pending exception by calling checkAndClearExceptions ().

bool QJniEnvironment:: checkAndClearExceptions ( QJniEnvironment::OutputMode outputMode = OutputMode::Verbose)

Cleans any pending exceptions either silently or reporting stack backtrace, depending on the outputMode .

In contrast to QJniObject , which handles exceptions internally, if you make JNI calls directly via JNIEnv , you need to clear any potential exceptions after the call using this function. For more information about JNIEnv calls that can throw an exception, see JNI Functions .

返回 true when a pending exception was cleared.

`[static]` bool QJniEnvironment:: checkAndClearExceptions ( JNIEnv * env , QJniEnvironment::OutputMode outputMode = OutputMode::Verbose)

Cleans any pending exceptions for env , either silently or reporting stack backtrace, depending on the outputMode . This is useful when you already have a JNIEnv pointer such as in a native function implementation.

返回 true when a pending exception was cleared.

jclass QJniEnvironment:: findClass (const char * className )

搜索 className using all available class loaders. Qt on Android uses a custom class loader to load all the .jar files and it must be used to find any classes that are created by that class loader because these classes are not visible when using the default class loader.

Returns the class pointer or null if className 找不到。

A use case for this function is searching for a class to call a JNI method that takes a jclass . This can be useful when doing multiple JNI calls on the same class object which can a bit faster than using a class name in each call. Additionally, this call looks for internally cached classes first before doing a JNI call, and returns such a class if found. The following code snippet creates an instance of the class CustomClass and then calls the printFromJava() 方法：

QJniEnvironment env;
jclass javaClass = env.findClass("org/qtproject/example/android/CustomClass");
QJniObject javaMessage = QJniObject::fromString("findClass example");
QJniObject::callStaticMethod<void>(javaClass, "printFromJava",
                                   "(Ljava/lang/String;)V", javaMessage.object<jstring>());

注意： This call returns a global reference to the class object from the internally cached classes.

`[since 6.2]` jfieldID QJniEnvironment:: findField ( jclass clazz , const char * fieldName , const char * signature )

Searches for a member field of a class clazz . The field is specified by its fieldName and signature .

Returns the field ID or nullptr if the field is not found.

A usecase for this method is searching for class fields and caching their IDs, so that they could later be used for getting/setting the fields.

该函数在 Qt 6.2 引入。

`[since 6.4]` template <typename T> jfieldID QJniEnvironment:: findField ( jclass clazz , const char * fieldName )

Searches for a member field of a class clazz . The field is specified by its fieldName . The signature of the field is deduced from the template parameter.

Returns the field ID or nullptr if the field is not found.

该函数在 Qt 6.4 引入。

`[since 6.2]` jmethodID QJniEnvironment:: findMethod ( jclass clazz , const char * methodName , const char * signature )

Searches for an instance method of a class clazz . The method is specified by its methodName and signature .

Returns the method ID or nullptr if the method is not found.

A usecase for this method is searching for class methods and caching their IDs, so that they could later be used for calling the methods.

该函数在 Qt 6.2 引入。

`[since 6.4]` template <typename Args> jmethodID QJniEnvironment:: findMethod ( jclass clazz , const char * methodName )

Searches for an instance method of a class clazz . The method is specified by its methodName , the signature is deduced from the template parameters.

Returns the method ID or nullptr if the method is not found.

该函数在 Qt 6.4 引入。

`[since 6.2]` jfieldID QJniEnvironment:: findStaticField ( jclass clazz , const char * fieldName , const char * signature )

Searches for a static field of a class clazz . The field is specified by its fieldName and signature .

Returns the field ID or nullptr if the field is not found.

A usecase for this method is searching for class fields and caching their IDs, so that they could later be used for getting/setting the fields.

该函数在 Qt 6.2 引入。

`[since 6.4]` template <typename T> jfieldID QJniEnvironment:: findStaticField ( jclass clazz , const char * fieldName )

Searches for a static field of a class clazz . The field is specified by its fieldName . The signature of the field is deduced from the template parameter.

Returns the field ID or nullptr if the field is not found.

该函数在 Qt 6.4 引入。

`[since 6.2]` jmethodID QJniEnvironment:: findStaticMethod ( jclass clazz , const char * methodName , const char * signature )

Searches for a static method of a class clazz . The method is specified by its methodName and signature .

Returns the method ID or nullptr if the method is not found.

A usecase for this method is searching for class methods and caching their IDs, so that they could later be used for calling the methods.

QJniEnvironment env;
jclass javaClass = env.findClass("org/qtproject/example/android/CustomClass");
jmethodID methodId = env.findStaticMethod(javaClass,
                                          "staticJavaMethod",
                                          "(Ljava/lang/String;)V");
QJniObject javaMessage = QJniObject::fromString("findStaticMethod example");
QJniObject::callStaticMethod<void>(javaClass,
                                   methodId,
                                   javaMessage.object<jstring>());

该函数在 Qt 6.2 引入。

`[since 6.4]` template <typename Args> jmethodID QJniEnvironment:: findStaticMethod ( jclass clazz , const char * methodName )

Searches for an instance method of a class clazz . The method is specified by its methodName , the signature is deduced from the template parameters.

Returns the method ID or nullptr if the method is not found.

QJniEnvironment env;
jclass javaClass = env.findClass("org/qtproject/example/android/CustomClass");
jmethodID methodId = env.findStaticMethod<void, jstring>(javaClass, "staticJavaMethod");
QJniObject javaMessage = QJniObject::fromString("findStaticMethod example");
QJniObject::callStaticMethod<void>(javaClass,
                                   methodId,
                                   javaMessage.object<jstring>());

该函数在 Qt 6.4 引入。

`[since 6.2]` bool QJniEnvironment:: isValid () const

返回 true if this instance holds a valid JNIEnv object.

该函数在 Qt 6.2 引入。

`[static]` JavaVM *QJniEnvironment:: javaVM ()

Returns the Java VM interface for the current process. Although it might be possible to have multiple Java VMs per process, Android allows only one.

JNIEnv *QJniEnvironment:: jniEnv () const

Returns the JNI Environment's JNIEnv 指针。

bool QJniEnvironment:: registerNativeMethods (const char * className , const JNINativeMethod [] methods , int size )

Registers the Java methods in the array methods 的大小 size , each of which can call native C++ functions from class className . These methods must be registered before any attempt to call them.

返回 true if the registration is successful, otherwise false .

Each element in the methods array consists of:

The Java method name
Method signature
The C++ functions that will be executed

const JNINativeMethod methods[] =
                        {{"callNativeOne", "(I)V", reinterpret_cast<void *>(fromJavaOne)},
                        {"callNativeTwo", "(I)V", reinterpret_cast<void *>(fromJavaTwo)}};
QJniEnvironment env;
env.registerNativeMethods("org/qtproject/android/TestJavaClass", methods, 2);

bool QJniEnvironment:: registerNativeMethods ( jclass clazz , const JNINativeMethod [] methods , int size )

这是重载函数。

This overload uses a previously cached jclass instance clazz .

JNINativeMethod methods[] {{"callNativeOne", "(I)V", reinterpret_cast<void *>(fromJavaOne)},
                           {"callNativeTwo", "(I)V", reinterpret_cast<void *>(fromJavaTwo)}};
QJniEnvironment env;
jclass clazz = env.findClass("org/qtproject/android/TestJavaClass");
env.registerNativeMethods(clazz, methods, 2);

JNIEnv &QJniEnvironment:: operator* () const

Returns the JNI Environment's JNIEnv 对象。

JNIEnv *QJniEnvironment:: operator-> () const

Provides access to the JNI Environment's JNIEnv 指针。

QJniEnvironment 类

公共类型

公共函数

静态公共成员

详细描述

成员类型文档编制

enum class QJniEnvironment:: OutputMode

成员函数文档编制

QJniEnvironment:: QJniEnvironment ()

QJniEnvironment:: ~QJniEnvironment ()

bool QJniEnvironment:: checkAndClearExceptions ( QJniEnvironment::OutputMode outputMode = OutputMode::Verbose)

[static] bool QJniEnvironment:: checkAndClearExceptions ( JNIEnv * env , QJniEnvironment::OutputMode outputMode = OutputMode::Verbose)

jclass QJniEnvironment:: findClass (const char * className )

[since 6.2] jfieldID QJniEnvironment:: findField ( jclass clazz , const char * fieldName , const char * signature )

[since 6.4] template <typename T> jfieldID QJniEnvironment:: findField ( jclass clazz , const char * fieldName )

[since 6.2] jmethodID QJniEnvironment:: findMethod ( jclass clazz , const char * methodName , const char * signature )

[since 6.4] template <typename Args> jmethodID QJniEnvironment:: findMethod ( jclass clazz , const char * methodName )

[since 6.2] jfieldID QJniEnvironment:: findStaticField ( jclass clazz , const char * fieldName , const char * signature )

[since 6.4] template <typename T> jfieldID QJniEnvironment:: findStaticField ( jclass clazz , const char * fieldName )

[since 6.2] jmethodID QJniEnvironment:: findStaticMethod ( jclass clazz , const char * methodName , const char * signature )

[since 6.4] template <typename Args> jmethodID QJniEnvironment:: findStaticMethod ( jclass clazz , const char * methodName )

[since 6.2] bool QJniEnvironment:: isValid () const

[static] JavaVM *QJniEnvironment:: javaVM ()

JNIEnv *QJniEnvironment:: jniEnv () const

bool QJniEnvironment:: registerNativeMethods (const char * className , const JNINativeMethod [] methods , int size )

bool QJniEnvironment:: registerNativeMethods ( jclass clazz , const JNINativeMethod [] methods , int size )

JNIEnv &QJniEnvironment:: operator* () const

JNIEnv *QJniEnvironment:: operator-> () const

内容

`[static]` bool QJniEnvironment:: checkAndClearExceptions ( JNIEnv * env , QJniEnvironment::OutputMode outputMode = OutputMode::Verbose)

`[since 6.2]` jfieldID QJniEnvironment:: findField ( jclass clazz , const char * fieldName , const char * signature )

`[since 6.4]` template <typename T> jfieldID QJniEnvironment:: findField ( jclass clazz , const char * fieldName )

`[since 6.2]` jmethodID QJniEnvironment:: findMethod ( jclass clazz , const char * methodName , const char * signature )

`[since 6.4]` template <typename Args> jmethodID QJniEnvironment:: findMethod ( jclass clazz , const char * methodName )

`[since 6.2]` jfieldID QJniEnvironment:: findStaticField ( jclass clazz , const char * fieldName , const char * signature )

`[since 6.4]` template <typename T> jfieldID QJniEnvironment:: findStaticField ( jclass clazz , const char * fieldName )

`[since 6.2]` jmethodID QJniEnvironment:: findStaticMethod ( jclass clazz , const char * methodName , const char * signature )

`[since 6.4]` template <typename Args> jmethodID QJniEnvironment:: findStaticMethod ( jclass clazz , const char * methodName )

`[since 6.2]` bool QJniEnvironment:: isValid () const

`[static]` JavaVM *QJniEnvironment:: javaVM ()