ANT未关联JNI文件，APK未编译Java/C++代码问题求助

最近我在尝试纯终端/控制台环境下搭建带JNI的Android项目——全程不用任何IDE（尤其是谷歌系的），也不想碰Gradle，但遇到了挺头疼的问题：编译出来的.apk虽然能启动，但完全没用到我自己写的Java和C++代码，ANT构建工具反而生成了一套新的Java模板，然后基于那个模板编译出了安装包。更闹心的是，我翻了好多资料，都没找到一套完善的纯终端构建手册。

我的项目结构 #

.
├── cpp
│   ├── jni
│   │   ├── com_example_jnihelloworld_jniactivity.h
│   │   ├── jniactivity.h
│   │   ├── jniactivity.cpp
│   │   ├── jniimplement.cpp
│   │   ├── Application.mk
│   │   └── Android.mk
│   ├── libs
│   └── obj
├── java
│   ├── src
│   │   └── com
│   │       └── example
│   │           └── jnihelloworld
│   │               └── jniactivity.java
│   ├── bin
│   │   └── com
│   │       └── example
│   │           └── jnihelloworld
│   │               └── jniactivity.class
│   └── pcmp

我执行的命令 #

ndk-build
android create project --target android-24 --name HelloJni --path .\pcmp --activity jniact --package com.example.jnihelloworld
ant debug -f .\pcmp

我写的Java源码 #

package com.example.jnihelloworld;
import android.os.Bundle;
import android.app.Activity;
import android.widget.TextView;
public class jniactivity extends Activity {
    static {
        System.loadLibrary("myjni");
    }
    public native String getMessage();
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        TextView textView = new TextView(this);
        textView.setText(getMessage());
        setContentView(textView);
    }
}

我的C++源码 #

#include "com_example_jnihelloworld_jniactivity.h"
#include "jniactivity.h"
JNIEXPORT jstring JNICALL Java_com_example_jnihelloworld_jniactivity_getMessage
(JNIEnv *pEnv, jobject pThis) {
    std::cout << "One" << std::endl;
    return pEnv->NewStringUTF("Hello from native code!");
}

自动生成的ANT脚本 #

<?xml version="1.0" encoding="UTF-8"?>
<project name="HelloJni" default="help">
<!-- The local.properties file is created and updated by the 'android' tool. It contains the path to the SDK. It should *NOT* be checked into Version Control Systems. -->
<property file="local.properties" />
<!-- The ant.properties file can be created by you. It is only edited by the 'android' tool to add properties to it. This is the place to change some Ant specific build properties. Here are some properties you may want to change/update: source.dir The name of the source directory. Default is 'src'. out.dir The name of the output directory. Default is 'bin'. For other overridable properties, look at the beginning of the rules files in the SDK, at tools/ant/build.xml Properties related to the SDK location or the project target should be updated using the 'android' tool with the 'update' action. This file is an integral part of the build system for your application and should be checked into Version Control Systems. -->
<property file="ant.properties" />
<!-- if sdk.dir was not set from one of the property file, then get it from the ANDROID_HOME env var. This must be done before we load project.properties since the proguard config can use sdk.dir -->
<property environment="env" />
<condition property="sdk.dir" value="${env.ANDROID_HOME}">
<isset property="env.ANDROID_HOME" />
</condition>
<!-- The project.properties file is created and updated by the 'android' tool, as well as ADT. This contains project specific properties such as project target, and library dependencies. Lower level build properties are stored in ant.properties (or in .classpath for Eclipse projects). This file is an integral part of the build system for your application and should be checked into Version Control Systems. -->
<loadproperties srcFile="project.properties" />
<!-- quick check on sdk.dir -->
<fail message="sdk.dir is missing. Make sure to generate local.properties using 'android update project' or to inject it through the ANDROID_HOME environment variable." unless="sdk.dir" />
<!-- Import per project custom build rules if present at the root of the project. This is the place to put custom intermediary targets such as: -pre-build -pre-compile -post-compile (This is typically used for code obfuscation. Compiled code location: ${out.classes.absolute.dir} If this is not done in place, override ${out.dex.input.absolute.dir}) -post-package -post-build -pre-clean -->
<import file="custom_rules.xml" optional="true" />
<!-- Import the actual build file. To customize existing targets, there are two options: - Customize only one target: - copy/paste the target into this file, *before* the <import> task. - customize it to your needs. - Customize the whole content of build.xml - copy/paste the content of the rules files (minus the top node) into this file, replacing the <import> task. - customize to your needs. *********************** ****** IMPORTANT ****** *********************** In all cases you must update the value of version-tag below to read 'custom' instead of an integer, in order to avoid having your file be overridden by tools such as "android update project" -->
<!-- version-tag: 1 -->
<import file="${sdk.dir}/tools/ant/build.xml" />
</project>

问题根源与解决方向 #

1. ANT用了新模板，没识别你的代码 #

你执行的android create project命令在pcmp目录下生成了一套全新的项目模板，包括默认的Java文件（比如jniact.java），而ANT默认只会编译这个目录下src里的代码，根本没去读取你java/src下的自定义代码。

解决办法：

• 别用android create project生成新项目，而是在你现有的项目结构上初始化ANT环境：进入java目录，执行android update project --path . --target android-24 --name HelloJni，这样ANT会适配你现有的源码结构，不会生成新模板。
• 如果一定要用pcmp目录，把你java/src下的com目录整个复制到pcmp/src下，覆盖默认生成的文件，这样ANT就会编译你的代码了。

2. NDK编译的库没被ANT打包进APK #

你的ndk-build生成的.so文件在cpp/libs目录下，但ANT默认只会寻找项目根目录下libs里的native库，所以你的C++代码产物根本没被打包进去。

解决办法：

• 在ant.properties里添加ndk.dir=/path/to/your/ndk，ANT会自动调用NDK构建；或者手动把cpp/libs下的所有架构目录（比如armeabi-v7a）复制到ANT项目的libs目录下，确保打包时包含.so文件。
• 也可以修改Android.mk，指定LOCAL_MODULE_PATH为ANT项目的libs目录，让ndk-build直接把库生成到正确位置。

3. 纯终端构建的参考流程 #

虽然官方现在主推Gradle，但纯ANT+NDK的终端构建还是可行的，大致步骤如下：

1. 整理好你的Java源码和JNI代码目录结构。
2. 用android update project初始化ANT项目（不要用create）。
3. 在local.properties里配置ndk.dir和sdk.dir，或者通过环境变量ANDROID_HOME、NDK_HOME指定。
4. 先执行ndk-build编译native代码，再执行ant debug/ant release打包APK。
5. 如果需要自定义构建逻辑，可以写custom_rules.xml扩展ANT步骤，比如自动触发NDK构建、指定自定义源码目录等。

内容的提问来源于stack exchange，提问作者cname