接口代理实现 Android Application 的多继承

接口代理实现 Android Application 的多继承

在项目开发中，当我们接入第三方 SDK 时，可能会要求我们自己的 Application 继承它们的 Application , 但是 Java 只能是单继承的，这时我们就可以使用接口代理的方式来间接地实现“多继承”了。

假设我们的 MyApplication 需要继承两个第三方 SDK 的类 XApplication 与 YApplication .(本文以百度地图BmfMapApplication和FlutterApplication为例)

显然，我们自家的 MyApplication 是不可能同时直接继承上面的两个 Application 的。我们可以让 MyApplication 继承一个代理类 ProxyApplication , 然后在 ProxyApplication 中通过反射和接口回调的方式调用组合实现类 ApplicationImpl（组合了多个 Application 接口）对应的方法。 

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package top.w2gd.wit_niit;

import android.content.Context;
import android.content.res.Configuration;
import android.util.Log;

public class MyApplication extends ProxyApplication {

    @Override
    protected void attachBaseContext(Context base) {
        super.attachBaseContext(base);

        Log.d("info-->", "MyApplication attachBaseContext");
    }

    @Override
    public void onCreate() {
        super.onCreate();

        Log.d("info-->", "MyApplication onCreate");
    }

    @Override
    public void onConfigurationChanged(Configuration newConfig) {
        super.onConfigurationChanged(newConfig);

        Log.d("info-->", "MyApplication onConfigurationChanged");
    }
}
package top.w2gd.wit_niit;

import android.app.Application;
import android.content.Context;
import android.content.res.Configuration;

public class ProxyApplication extends Application {

    private IApplicationListener iApplicationListener;

    @Override
    protected void attachBaseContext(Context base) {
        super.attachBaseContext(base);

        iApplicationListener = getProxyApplication();

        if (iApplicationListener != null) {
            iApplicationListener.onProxyAttachBaseContext(base);
        }
    }

    @Override
    public void onCreate() {
        super.onCreate();

        if (iApplicationListener != null) {
            iApplicationListener.onProxyCreate();
        }
    }

    @Override
    public void onConfigurationChanged(Configuration newConfig) {
        super.onConfigurationChanged(newConfig);

        if (iApplicationListener != null) {
            iApplicationListener.onProxyConfigurationChanged(newConfig);
        }
    }

    private IApplicationListener getProxyApplication() {
        try {
            Class clazz = Class.forName("top.w2gd.wit_niit.ApplicationImpl");
            return (IApplicationListener) clazz.newInstance();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (InstantiationException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        }
        return null;
    }
}

在组合实现类 ApplicationImpl 中，我们通过反射代理的方式调用多个 Application 的生命周期方法。 

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package top.w2gd.wit_niit;

import android.app.Application;
import android.content.Context;
import android.content.res.Configuration;

public class ApplicationImpl extends Application implements IApplicationListener {

    private IXApplicationListener ixApplicationListener;
    private IYApplicationListener iyApplicationListener;

    @Override
    public void onProxyAttachBaseContext(Context base) {
        super.attachBaseContext(base);

        ixApplicationListener = getXApplication();
        iyApplicationListener = getYApplication();

        if (ixApplicationListener != null) {
            ixApplicationListener.onXAttachBaseContext(base);
        }
        if (iyApplicationListener != null) {
            iyApplicationListener.onYAttachBaseContext(base);
        }
    }

    @Override
    public void onProxyCreate() {
        super.onCreate();

        if (ixApplicationListener != null) {
            ixApplicationListener.onXCreate();
        }
        if (iyApplicationListener != null) {
            iyApplicationListener.onYCreate();
        }
    }

    @Override
    public void onProxyConfigurationChanged(Configuration newConfig) {
        super.onConfigurationChanged(newConfig);

        if (ixApplicationListener != null) {
            ixApplicationListener.onXConfigurationChanged(newConfig);
        }
        if (iyApplicationListener != null) {
            iyApplicationListener.onYConfigurationChanged(newConfig);
        }
    }

    private IXApplicationListener getXApplication() {
        Class clazz = null;
        try {
            clazz = Class.forName("top.w2gd.wit_niit.XApplicationImpl");
            return (IXApplicationListener) clazz.newInstance();
        } catch (InstantiationException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
        return null;
    }

    private IYApplicationListener getYApplication() {
        Class clazz = null;
        try {
            clazz = Class.forName("top.w2gd.wit_niit.YApplicationImpl");
            return (IYApplicationListener) clazz.newInstance();
        } catch (InstantiationException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
        return null;
    }
}

接口 IApplicationListener 

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package top.w2gd.wit_niit;

import android.content.Context;
import android.content.res.Configuration;

public interface IApplicationListener {

    void onProxyAttachBaseContext(Context base);

    void onProxyCreate();

    void onProxyConfigurationChanged(Configuration newConfig);
}

实现类 XApplicationImpl 

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package top.w2gd.wit_niit;

import android.content.Context;
import android.content.res.Configuration;

import com.baidu.mapapi.base.BmfMapApplication;

public class XApplicationImpl extends BmfMapApplication implements IXApplicationListener {


    @Override
    public void onXAttachBaseContext(Context base) {
        super.attachBaseContext(base);
    }

    @Override
    public void onXCreate() {
        super.onCreate();
    }

    @Override
    public void onXConfigurationChanged(Configuration newConfig) {
        super.onConfigurationChanged(newConfig);
    }
}

接口 IXApplicationListener 

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package top.w2gd.wit_niit;

import android.content.Context;
import android.content.res.Configuration;

public interface IXApplicationListener {

    void onXAttachBaseContext(Context base);

    void onXCreate();

    void onXConfigurationChanged(Configuration newConfig);
}

实现类 YApplicationImpl 

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package top.w2gd.wit_niit;

import android.content.Context;
import android.content.res.Configuration;

import cn.leancloud.LCLogger;
import cn.leancloud.LeanCloud;
import cn.leancloud.im.LCIMOptions;
import io.flutter.app.FlutterApplication;

public class YApplicationImpl extends FlutterApplication implements IYApplicationListener {
    private static final String LC_App_Id = "DtL8wv4T5fXStZXc3Vu8b1Ov-gzGzoHsz";
    private static final String LC_App_Key = "AcSQcHf3pkFPCDKQP27CSWwu";
    private static final String LC_Server_Url = "https://niit.w2gd.top";

    @Override
    public void onYAttachBaseContext(Context base) {
        super.attachBaseContext(base);
    }

    @Override
    public void onYCreate() {
        super.onCreate();
        LCIMOptions.getGlobalOptions().setUnreadNotificationEnabled(true);

        LeanCloud.setLogLevel(LCLogger.Level.DEBUG);
        LeanCloud.initialize(this, LC_App_Id, LC_App_Key, LC_Server_Url);
    }

    @Override
    public void onYConfigurationChanged(Configuration newConfig) {
        super.onConfigurationChanged(newConfig);
    }
}

接口 IYApplicationListener 

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package top.w2gd.wit_niit;

import android.content.Context;
import android.content.res.Configuration;

public interface IYApplicationListener {
    void onYAttachBaseContext(Context base);

    void onYCreate();

    void onYConfigurationChanged(Configuration newConfig);
}

当我们在清单文件中声明了 MyApplication 并跑起项目时，会打印以下日志：

08-03 13:56:33.830 9314-9314/? D/info–>: XApplication attachBaseContext
08-03 13:56:33.830 9314-9314/? D/info–>: YApplication attachBaseContext
08-03 13:56:33.830 9314-9314/? D/info–>: MyApplication attachBaseContext
08-03 13:56:33.830 9314-9314/? D/info–>: XApplication onCreate
08-03 13:56:33.830 9314-9314/? D/info–>: YApplication onCreate
08-03 13:56:33.830 9314-9314/? D/info–>: MyApplication onCreate
说明我们在 MyApplication 中成功地调用了 XApplication 与 YApplication 中的生命周期方法。