Question

我试图从NDKTest.c文件中调用stringFromJNI2（env，obj）函数。

以下是NDKTest.c文件的代码：

#include <string.h>

#include <stdio.h>
#include <jni.h>
#include <limits.h>

JNIEXPORT jstring JNICALL
Java_com_test_ndk_NDKTest_stringFromJNI2( JNIEnv *env,
                                              jobject thiz )
{
#if defined(__arm__)
#if defined(__ARM_ARCH_7A__)
#if defined(__ARM_NEON__)
  #if defined(__ARM_PCS_VFP)
    #define ABI "armeabi-v7a/NEON (hard-float)"
  #else
    #define ABI "armeabi-v7a/NEON"
  #endif
#else
  #if defined(__ARM_PCS_VFP)
    #define ABI "armeabi-v7a (hard-float)"
  #else
    #define ABI "armeabi-v7a"
  #endif
#endif
#else
#define ABI "armeabi"
#endif
#elif defined(__i386__)
#define ABI "x86"
#elif defined(__x86_64__)
#define ABI "x86_64"
#elif defined(__mips64)  /* mips64el-* toolchain defines __mips__ too */
#define ABI "mips64"
#elif defined(__mips__)
#define ABI "mips"
#elif defined(__aarch64__)
#define ABI "arm64-v8a"
#else
#define ABI "unknown"
#endif

return (*env)->NewStringUTF(env, "Hello from JNI2 !  Compiled with ABI " ABI ".");

}

以下是NDKTest.h文件的代码：

#ifndef NDKTEST_H_
#define NDKTEST_H_

#include <jni.h>
#include <string>

const std::allocator<char> & stringFromJNI2(JNIEnv *env, jobject thiz);

#endif

以下是TestNDK.cpp文件的代码：

#include <string.h>
#include <jni.h>

#include <string>
#include <jni.h>

#include "NDKTest.h"

extern "C" {
    stringFromJNI2(JNIEnv *env, jobject obj);
}

JNIEXPORT jstring JNICALL
Java_com_test_ndk_TestNDK_main(JNIEnv *env, jobject obj) {
#if defined(__arm__)
#if defined(__ARM_ARCH_7A__)
#if defined(__ARM_NEON__)
#define ABI "armeabi-v7a/NEON"
#else
#define ABI "armeabi-v7a"
#endif
#else
#define ABI "armeabi"
#endif
#elif defined(__i386__)
#define ABI "x86"
#endif
    //std::string hello("Hello from JNI !  Compiled with ABI " ABI ".");
    std::string hello(stringFromJNI2(env, obj));
    return env->NewStringUTF(hello.c_str());
}

以下是TestNDK.java文件的代码：

package com.test.ndk;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.TextView;

public class TestNDK extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    /* Retrieve our TextView and set its content.
     * the text is retrieved by calling a native
     * function.
     */
    setContentView(R.layout.activity_hello_jni);
    TextView tv = (TextView)findViewById(R.id.hello_textview);
    tv.setText( main() );

    public native String main();

    static {
        //System.loadLibrary("main");
        System.loadLibrary("TestNDK");
    }
}

以下是CMakeLists.txt文件中的行：

cmake_minimum_required(VERSION 3.4.1)

add_library(testNDK SHARED
        TestNDK.cpp
        NDKTest.c)

# Include libraries needed for testNDK lib
target_link_libraries(testNDK
                  android
                  log)

以下是build.gradle文件中的代码：

apply plugin: 'com.android.application'

android {
    compileSdkVersion 25
    buildToolsVersion '25.0.2'
    defaultConfig {
        applicationId 'com.test.ndk'
        minSdkVersion 23
        targetSdkVersion 25
        versionCode 1
        versionName "1.0"
        externalNativeBuild {
            cmake {
                arguments '-DANDROID_TOOLCHAIN=clang'
            }
        }
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
    externalNativeBuild {
        cmake {
            path "src/main/cpp/CMakeLists.txt"
        }
    }
    productFlavors {
        arm7 {
            // in the future, ndk.abiFilter might also work
            ndk {
                abiFilter 'armeabi-v7a'
            }
        }
        arm8 {
            ndk {
                abiFilters 'arm64-v8a'
            }
        }
        arm {
            ndk {
                abiFilter 'armeabi'
            }
        }
        x86 {
            ndk {
                abiFilter 'x86'
            }
        }
        x86_64 {
            ndk {
                abiFilter 'x86_64'
            }
        }
        mips {
            ndk {
                abiFilters 'mips', 'mips64'
            }
        }
        universal {
            ndk {
                abiFilters 'mips', 'mips64', 'x86', 'x86_64'
            }
        }
    }
}

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    compile 'com.android.support:appcompat-v7:25.2.0'
    compile 'com.android.support.constraint:constraint-layout:1.0.1'
}

我目前收到以下错误＆＃34;错误：（10,1）错误：C ++需要所有声明的类型说明符＆＃34; ＆安培; ＆＃34;错误：（29,23）错误：拨打＆＃39; stringFromJNI2＆＃39;暧昧＆＃34;由于TestNDK.cpp中的以下代码行：

stringFromJNI2(JNIEnv *env, jobject obj);

此代码行位于extern＆＃34; C＆＃34;代码块。我试图从TestNDK.cpp文件中调用NDKTest.c文件中的stringFromJni2（）函数。我如何修复我收到的当前错误并调用NDKTest.c文件中的stringFromJNI2（）函数来显示来自JNI2的＆＃34; Hello！用ABI编译＆＃34;串。任何有关这方面的帮助将不胜感激。感谢。

Answer 1

我正在尝试从TestNDK.cpp文件调用NDKTest.c文件中的stringFromJni2（）函数。

您应该在NDKTest.c中的NDKTest.h声明函数原型。所以标题应如下所示：

#ifndef NDKTEST_H_
#define NDKTEST_H_

#include <jni.h>

#ifdef __cplusplus
extern "C" {
#endif

jstring Java_com_test_ndk_NDKTest_stringFromJNI2(JNIEnv *env, jobject thiz);

#ifdef __cplusplus
}
#endif

#endif

TestNDK.cpp：

#include <jni.h>

#include "NDKTest.h"

#ifdef __cplusplus
extern "C" {
#endif

// remove this declaration
// stringFromJNI2(JNIEnv *env, jobject obj);

JNIEXPORT jstring JNICALL
Java_com_test_ndk_TestNDK_main(JNIEnv *env, jobject obj) {
#if defined(__arm__)
#if defined(__ARM_ARCH_7A__)
#if defined(__ARM_NEON__)
#define ABI "armeabi-v7a/NEON"
#else
#define ABI "armeabi-v7a"
#endif
#else
#define ABI "armeabi"
#endif
#elif defined(__i386__)
#define ABI "x86"
#endif
    return Java_com_test_ndk_NDKTest_stringFromJNI2(env, obj);
}

#ifdef __cplusplus
}
#endif

TestNDK.java：

// the library name has to be the same
// as you defined in CMakeLists.txt
static {
    System.loadLibrary("testNDK");
}

在Android JNI / NDK代码中从C ++函数调用C函数

1 个答案: