一、用Android Studio创建个空工程

二、把classes.jar拷到libs下

E:\software\Unity5_5\Editor\Data\PlaybackEngines\AndroidPlayer\Variations\mono\Release\Classes\classes.jar
拷到
D:\h5\GradleProjects\GameSupport\app\libs\classes.jar

注意：以上是我的安装目录和工程目录。

三、把classes.jar添加进Dependencies

四、删除res下多余的资源

五、修改build.gradle文件才能生成aar

修改后的文件

//apply plugin: 'com.android.application'
apply plugin: 'com.android.library'

android {
    compileSdkVersion 25
    buildToolsVersion "25.0.2"
    defaultConfig {
        //applicationId "com.zwwx.game.gamesupport"
        minSdkVersion 15
        targetSdkVersion 25
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    compile fileTree(include: ['*.jar'], dir: 'libs')
    androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {
        exclude group: 'com.android.support', module: 'support-annotations'
    })
    compile 'com.android.support:appcompat-v7:25.3.1'
    compile 'com.android.support.constraint:constraint-layout:1.0.2'
    testCompile 'junit:junit:4.12'
    compile files('libs/classes.jar')
}

六、修改AndroidManifest.xml

修改后的文件

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.zwwx.game.gamesupport">
    <uses-permission android:name="android.permission.INTERNET"></uses-permission>
    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@android:style/Theme.NoTitleBar">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
            <meta-data android:name="unityplayer.UnityActivity" android:value="true" />
        </activity>
    </application>
</manifest>

七、修改MainActivity.java

package com.zwwx.game.gamesupport;

import android.os.Bundle;
import android.widget.Toast;
import com.unity3d.player.UnityPlayerActivity;

public class MainActivity extends UnityPlayerActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

    // 显示Toast消息
    public void ShowToast(final String message){
        runOnUiThread(new Runnable() {
            @Override
            public void run() {
                Toast.makeText(getApplicationContext(), message, Toast.LENGTH_LONG).show();
            }
        });
    }
}

八、生成arr

九、删除arr文件libs下的classes.jar

十、把aar和AS工程中的AndroidManifest.xml拷到Unity工程下

十一、创建test.cs

using UnityEngine;
public class Test : MonoBehaviour {
    void OnGUI()
    {
        if (GUI.Button(new Rect(200, 200, 200, 100), "Show Toest - Hello World!"))
        {
            AndroidHelper.Call("ShowToast", "Hello World!");
        }
    }
}

十二、设置好Player Settings，然后打包测试

十三、最后赠送一个Unity中调用java方法的辅助工具类

using System.Collections;
using System;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.Android;
/// <summary>
/// 与Android交互的辅助类
/// </summary>
public class AndroidHelper
{
    #if UNITY_ANDROID && !UNITY_EDITOR
    #region 获得主活动类
    public static AndroidJavaClass MainActivity
    {
        get
        {
            try
            {
                AndroidJavaClass player = new AndroidJavaClass("com.unity3d.player.UnityPlayer");
                return player;
            }
            catch (Exception)
            {
                return null;
            }
        }
    }
    #endregion

    #region 获得当前Android活动
    public static AndroidJavaObject currentActivity
    {
        get {
            try
            {
                AndroidJavaObject context = MainActivity.GetStatic<AndroidJavaObject>("currentActivity");
                return context;
            }
            catch (Exception)
            {
                return null;
            }
        }
    }
    #endregion

    #region 获得Java类
    public static AndroidJavaClass JavaClass(string className)
    {
        try
        {
            AndroidJavaClass java_class = new AndroidJavaClass(className);
            return java_class;
        }
        catch (Exception)
        {
            return null;
        }
    }
    #endregion

    #region 获得Java对象
    public static AndroidJavaObject JavaObject(string className, params object[] args)
    {
        try
        {
            AndroidJavaObject java_object = new AndroidJavaObject(className, args);
            return java_object;
        }
        catch (Exception)
        {
            return null;
        }
    }
    #endregion
    #endif

    #region 调用Java类的实例方法
    public static void Call(string methodName, params object[] args)
    {
        #if UNITY_ANDROID && !UNITY_EDITOR
        currentActivity.Call(methodName, args);
        #endif
    }

    public static T Call<T>(string methodName, params object[] args)
    {
        #if UNITY_ANDROID && !UNITY_EDITOR
        return currentActivity.Call<T>(methodName, args);
        #endif
        return default(T);
    }

    public static void CallClass(string className, string methodName, params object[] args)
    {
        #if UNITY_ANDROID && !UNITY_EDITOR
        AndroidJavaObject java_object = JavaObject(className);
        java_object.Call(methodName, args);
        #endif
    }

    public static T CallClass<T>(string className, string methodName, params object[] args)
    {
        #if UNITY_ANDROID && !UNITY_EDITOR
        AndroidJavaObject java_object = JavaObject(className);
        return java_object.Call<T>(methodName, args);
        #endif
        return default(T);
    }
    #endregion

    #region 调用Java类的静态方法
    public static void CallStatic(string methodName, params object[] args)
    {
        #if UNITY_ANDROID && !UNITY_EDITOR
        MainActivity.CallStatic(methodName, args);
        #endif
    }

    public static T CallStatic<T>(string methodName, params object[] args)
    {
        #if UNITY_ANDROID && !UNITY_EDITOR
        return MainActivity.CallStatic<T>(methodName, args);
        #endif
        return default(T);
    }

    public static void CallClassStatic(string className, string methodName, params object[] args)
    {
        #if UNITY_ANDROID && !UNITY_EDITOR
        AndroidJavaClass java_class = JavaClass(className);
        java_class.CallStatic(methodName, args);
        #endif
    }

    public static T CallClassStatic<T>(string className, string methodName, params object[] args)
    {
        #if UNITY_ANDROID && !UNITY_EDITOR
        AndroidJavaClass java_class = JavaClass(className);
        return java_class.CallStatic<T>(methodName, args);
        #endif
        return default(T);
    }
    #endregion

    #region 申请权限
    /// <summary>
    /// 请求用户权限
    /// 权限常量:
    /// Permission.Camera         访问摄像头
    /// Permission.Microphone     访问麦克风
    /// Permission.CoarseLocation 获取粗略位置信息（只要能连接上基站就可以访问到）
    /// Permission.FineLocation   获取精确位置信息（如GPS）
    /// Permission.ExternalStorageRead  读存储卡
    /// Permission.ExternalStorageWrite 写存储卡
    /// </summary>
    /// <param name="permission">Permission中定义的权限常量字符串</param>
    public static void RequestUserPermission(string permission)
    {
        #if UNITY_ANDROID && !UNITY_EDITOR
        if (!Permission.HasUserAuthorizedPermission(permission))
            Permission.RequestUserPermission(permission);
        #endif
    }
    #endregion

    #region 设置持续性能模式
    /// <summary>
    /// 设置持续性能模式。启用后，持续性能模式旨在在长时间内提供一致的性能水平。
    /// 长期运行的应用的性能可能会显著波动，因为系统会阻止系统芯片在设备组件达到温度限制时启动。
    /// 当应用失去焦点后会自动停止此模式。
    /// 使用条件:
    /// Android 7.0+
    /// </summary>
    /// <param name="enabled"></param>
    public static void SetSustainedPerformanceMode(bool enabled)
    {
        #if UNITY_2019_1_OR_NEWER && UNITY_ANDROID && !UNITY_EDITOR
        AndroidDevice.SetSustainedPerformanceMode(enabled);
        #endif
    }
    #endregion
}

PS：推荐另一篇博文

http://www.cnblogs.com/xtqqkss/p/6387271.html