[英]Can't succeed in calling a Java function from a C++ module with JNI
I'm trying to call a Java class function from a C++ file using JNI and I always get a crash. 我试图使用JNI从C ++文件中调用Java类函数,但我总是崩溃。 My C++ file is : 我的C ++文件是:
#include <jni.h>
#include <string>
extern "C" JNIEXPORT jstring
JNICALL
Java_MyPackage_MyApp_stringFromJNI(JNIEnv *env,jobject /* this */,int a,jobject v) {
jclass V = env->GetObjectClass(v);
jmethodID setName=env->GetMethodID(V,"setName","(Ljava/lang/String;)V");
env->CallVoidMethod(v,setName,"new name");
return env->NewStringUTF("Testsss");
}
The problem arises when I try to call the method. 当我尝试调用该方法时会出现问题。 In the logcat, I see this : 在logcat中,我看到了:
runtime.cc:500] JNI DETECTED ERROR IN APPLICATION: use of deleted global reference 0x785cd7227ac6
runtime.cc:500] from java.lang.String MyPackage.MyApp.stringFromJNI(int, MyPackage.V)
runtime.cc:500] "main" prio=5 tid=1 Runnable
runtime.cc:500] | group="main" sCount=0 dsCount=0 flags=0 obj=0x73f2d670 self=0x785ceecbea00
runtime.cc:500] | sysTid=7020 nice=-10 cgrp=default sched=0/0 handle=0x785cf3b94a08
runtime.cc:500] | state=R schedstat=( 167686135 3959959 183 ) utm=14 stm=2 core=2 HZ=100
runtime.cc:500] | stack=0x7ffe2c4fc000-0x7ffe2c4fe000 stackSize=8MB
runtime.cc:500] | held mutexes= "mutator lock"(shared held)
The code for my Java function is : 我的Java函数的代码是:
void setName(String name) {
this.name = name;
}
Any idea about what could be the root of the problem? 是否知道可能是问题的根源?
You can't call the method like that: 您不能这样调用方法:
env->CallVoidMethod(v,setName,"new name");
You have to construct a Java string first, and then pass that: 您必须先构造一个Java字符串,然后传递该字符串:
jstring str = env->NewStringUTF("new name");
env->CallVoidMethod(v, setName, str);
Otherwise the VM tries to interpret the passed const char*
as a global reference to a jlString
. 否则,VM尝试将传递的const char*
解释为对jlString
的全局引用。 But it can't find it, so you get that error. 但是找不到它,所以您会收到该错误。
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