从本地code错误调用Java函数 [英] Error calling java function from native code
问题描述
我要打电话从本地code的Java方法。我遵循的步骤: 调用从C ++中的Android 的Java方法
I want to call a java method from native code. I followed the steps given in: Calling a java method from c++ in Android
不过我的应用程序崩溃,在那里的Java函数被调用的地方。
However my application crashes at the place where the java function is called.
我的Java code为如下图所示:
My java code is as shown below:
package com.example.jnitry;
import android.os.Bundle;
import android.app.Activity;
import android.util.Log;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
public class MainActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Log.d("MYAPP","Ocreate entered....");
Button btn=(Button) findViewById(R.id.button1);
btn.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View arg0) {
// TODO Auto-generated method stub
mainfunc(8);
}
});
}
public void display(byte[] byt){
Log.d("MYAPP", "display() is entered....");
for(int i=0;i<byt.length;i++)
Log.d("MYAPP", "byt["+i+"]="+byt[i]);
Log.d("MYAPP", "display finished");
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.activity_main, menu);
return true;
}
public static native void mainfunc(int n);
static
{
System.loadLibrary("mylib");
}
}
我的母语code为如下图所示:
My native code is as shown below:
#include <jni.h>
#include "com_example_jnitry_MainActivity.h"
#include <android/log.h>
#include <stdio.h>
JNIEXPORT void JNICALL Java_com_example_jnitry_MainActivity_mainfunc
(JNIEnv *env, jclass obj, jint n){
__android_log_print(ANDROID_LOG_DEBUG,"MYAPP","mainfunction entered...",NULL);
int i;
unsigned char arr[10];
jbyteArray bArray=(*env)->NewByteArray(env,n);
jclass cls = (*env)->FindClass(env, "com/example/jnitry/MainActivity");
jmethodID mid = (*env)->GetMethodID(env, cls, "display", "([B)V");
if (mid == 0){
__android_log_print(ANDROID_LOG_DEBUG,"MYAPP","mid==0",NULL);
return;
}
if(bArray==NULL)
{ __android_log_print(ANDROID_LOG_DEBUG,"MYAPP","bArray==NULL...",NULL);
return ;
}
for(i=0;i<n;i++){
arr[i]=i;
__android_log_print(ANDROID_LOG_DEBUG,"MYAPP","Iteration number:%d",i);
}
(*env)->SetByteArrayRegion(env,bArray,0,n,arr);
__android_log_print(ANDROID_LOG_DEBUG,"MYAPP","bArray successfully created...",NULL);
(*env)->CallVoidMethod(env, obj, mid, bArray);
__android_log_print(ANDROID_LOG_DEBUG,"MYAPP","Returned from disp() java function.....",NULL);
}
打印日志消息后,我的应用程序崩溃:
My app crashes after printing the log message:
02-14 15:37:06.814: D/MYAPP(11584): bArray successfully created...
谁能告诉我的原因。并提供相同的溶液。先谢谢了。
Can anyone please tell me the reason. And provide a solution for the same. Thanks in advance.
注意:我已经尝试过的 CallVoidMedthodA() callByteMethod() CallObjectMethod(),但他们结果是一样的。
Note: I have already tried CallVoidMedthodA(), callByteMethod(), CallObjectMethod() but they outcome was the same.
推荐答案
您的本地方法 mainFunc
是一个静态方法 - 它没有一个有效的这个
指针。同时,显示
是一个实例方法 - 它需要一个
Your native method mainFunc
is a static method - it does not have a valid this
pointer. Meanwhile, display
is an instance method - it needs one.
mainFunc
的第二个参数实际上是 MainActivity
A类对象的指针,按照JNI的规则。声明 mainFunc
作为非静态的Java端,这将正常工作。
The second parameter of mainFunc
is actually a class object pointer for MainActivity
, as per JNI rules. Declare mainFunc
as nonstatic on Java side, and this will work.
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