Android 接口定义语言 (AIDL)

Android 接口定义语言 (AIDL) 与其他IDL类似:它允许您定义客户端和服务之间用于通过进程间通信 (IPC) 进行通信的编程接口。

在 Android 上,一个进程通常无法访问另一个进程的内存。为了通信,它们需要将对象分解为操作系统能够理解的基本类型,并为您跨越边界编组这些对象。编写编组代码十分繁琐,因此 Android 使用 AIDL 为您处理。

注意:仅当您允许来自不同应用的客户端通过 IPC 访问您的服务并且您希望在服务中处理多线程时,才需要 AIDL。如果您不需要在不同应用之间执行并发 IPC,则通过实现 Binder 来创建您的接口。如果您想执行 IPC 但不需要处理多线程,则使用 Messenger 实现您的接口。无论如何,在实现 AIDL 之前,请务必了解绑定服务

在您开始设计 AIDL 接口之前,请注意对 AIDL 接口的调用是直接函数调用。不要对调用发生的线程做出假设。根据调用是来自本地进程中的线程还是远程进程中的线程,情况会有所不同。

  • 来自本地进程的调用在进行调用的同一线程中执行。如果这是您的主界面线程,则该线程将继续在 AIDL 接口中执行。如果是另一个线程,则该线程将在服务中执行您的代码。因此,如果只有本地线程访问服务,您可以完全控制哪些线程在其中执行。但如果是这种情况,则根本不要使用 AIDL;而是通过实现 Binder 来创建接口。
  • 来自远程进程的调用从平台在您自己的进程中维护的线程池中分派。请准备好接收来自未知线程的传入调用,并且可能有多个调用同时发生。换句话说,AIDL 接口的实现必须完全线程安全。来自同一远程对象上一个线程的调用将按顺序到达接收端。
  • oneway 关键字会修改远程调用的行为。使用它时,远程调用不会阻塞。它会发送事务数据并立即返回。接口的实现最终会像从 Binder 线程池发出的常规调用一样接收此调用,如同正常的远程调用一样。如果 oneway 与本地调用一起使用,则没有影响,并且调用仍然是同步的。

定义 AIDL 接口

使用 Java 编程语言语法在 .aidl 文件中定义 AIDL 接口,然后将其保存在托管服务的应用和绑定到服务的任何其他应用的源代码 src/ 目录中。

当您构建包含 .aidl 文件的每个应用时,Android SDK 工具会基于 .aidl 文件生成一个 IBinder 接口,并将其保存在项目的 gen/ 目录中。服务必须根据需要实现 IBinder 接口。然后,客户端应用可以绑定到服务并从 IBinder 调用方法以执行 IPC。

要使用 AIDL 创建绑定服务,请遵循以下步骤,这些步骤在以下部分中进行了描述。

  1. 创建 .aidl 文件

    此文件定义了带有方法签名的编程接口。

  2. 实现接口

    Android SDK 工具会根据您的 .aidl 文件生成一个 Java 编程语言接口。此接口有一个名为 Stub 的内部抽象类,它扩展了 Binder 并实现了您的 AIDL 接口中的方法。您必须扩展 Stub 类并实现这些方法。

  3. 向客户端公开接口

    实现 Service 并重写 onBind() 以返回您的 Stub 类实现。

注意:首次发布后对 AIDL 接口所做的任何更改都必须保持向后兼容,以避免破坏使用您服务的其他应用。也就是说,由于您的 .aidl 文件必须复制到其他应用以便它们可以访问您服务的接口,因此您必须保持对原始接口的支持。

创建 .aidl 文件

AIDL 使用简单的语法,允许您声明一个带有一个或多个方法的接口,这些方法可以接受参数并返回值。参数和返回值可以是任何类型,甚至是其他 AIDL 生成的接口。

您必须使用 Java 编程语言构造 .aidl 文件。每个 .aidl 文件必须定义一个接口,并且只需要接口声明和方法签名。

默认情况下,AIDL 支持以下数据类型:

  • Java 编程语言中除 short 之外的所有基本类型(例如 intlongcharboolean 等)
  • 任何类型的数组,例如 int[]MyParcelable[]
  • String
  • CharSequence
  • List

    List 中的所有元素都必须是此列表中支持的数据类型之一,或者是您声明的其他 AIDL 生成的接口或 Parcelable。 List 可选择用作参数化类型类,例如 List<String>。尽管方法生成为使用 List 接口,但另一端接收的实际具体类始终是 ArrayList

  • Map

    Map 中的所有元素都必须是此列表中支持的数据类型之一,或者是您声明的其他 AIDL 生成的接口或 Parcelable。不支持参数化类型映射,例如 Map<String,Integer> 形式的映射。尽管方法生成为使用 Map 接口,但另一端接收的实际具体类始终是 HashMap。考虑使用 Bundle 作为 Map 的替代方案。

您必须为每个未列出的额外类型包含 import 语句,即使它们定义在与您的接口相同的包中。

在定义服务接口时,请注意:

  • 方法可以接受零个或多个参数,并且可以返回值或 void。
  • 所有非基本参数都需要一个方向标签来指示数据流向:inoutinout(请参阅下面的示例)。

    基本类型、StringIBinder 和 AIDL 生成的接口默认是 in,不能是其他类型。

    注意:将方向限制为真正需要的方向,因为编组参数开销很大。

  • .aidl 文件中包含的所有代码注释都包含在生成的 IBinder 接口中,除了 import 和 package 语句之前的注释。
  • 字符串和整型常量可以在 AIDL 接口中定义,例如 const int VERSION = 1;
  • 方法调用由 transact() 代码分派,该代码通常基于接口中的方法索引。因为这使得版本控制变得困难,所以您可以手动将事务代码分配给方法:void method() = 10;
  • 可空参数和返回类型必须使用 @nullable 进行注解。

这是一个 .aidl 文件示例:

// IRemoteService.aidl
package com.example.android;

// Declare any non-default types here with import statements.

/** Example service interface */
interface IRemoteService {
    /** Request the process ID of this service. */
    int getPid();

    /** Demonstrates some basic types that you can use as parameters
     * and return values in AIDL.
     */
    void basicTypes(int anInt, long aLong, boolean aBoolean, float aFloat,
            double aDouble, String aString);
}

将您的 .aidl 文件保存在项目的 src/ 目录中。构建应用程序时,SDK 工具会在项目的 gen/ 目录中生成 IBinder 接口文件。生成的文件名与 .aidl 文件名匹配,但扩展名为 .java。例如,IRemoteService.aidl 会生成 IRemoteService.java

如果您使用 Android Studio,增量构建几乎会立即生成 Binder 类。如果您不使用 Android Studio,Gradle 工具会在下次构建应用程序时生成 Binder 类。在完成 .aidl 文件编写后,立即使用 gradle assembleDebuggradle assembleRelease 构建项目,以便您的代码可以链接到生成的类。

实现接口

当您构建应用程序时,Android SDK 工具会生成一个以您的 .aidl 文件命名的 .java 接口文件。生成的接口包含一个名为 Stub 的子类,它是其父接口(例如 YourInterface.Stub)的抽象实现,并声明了 .aidl 文件中的所有方法。

注意: Stub 还定义了一些辅助方法,最值得注意的是 asInterface(),它接受一个 IBinder(通常是传递给客户端的 onServiceConnected() 回调方法),并返回一个 stub 接口实例。有关如何进行此类型转换的更多详细信息,请参阅调用 IPC 方法部分。

要实现从 .aidl 生成的接口,请扩展生成的 Binder 接口(例如 YourInterface.Stub),并实现从 .aidl 文件继承的方法。

以下是使用匿名实例实现的名为 IRemoteService 接口的示例,该接口由前面 IRemoteService.aidl 示例定义:

Kotlin

private val binder = object : IRemoteService.Stub() {

    override fun getPid(): Int =
            Process.myPid()

    override fun basicTypes(
            anInt: Int,
            aLong: Long,
            aBoolean: Boolean,
            aFloat: Float,
            aDouble: Double,
            aString: String
    ) {
        // Does nothing.
    }
}

Java

private final IRemoteService.Stub binder = new IRemoteService.Stub() {
    public int getPid(){
        return Process.myPid();
    }
    public void basicTypes(int anInt, long aLong, boolean aBoolean,
        float aFloat, double aDouble, String aString) {
        // Does nothing.
    }
};

现在,binderStub 类的一个实例(一个 Binder),它定义了服务的 IPC 接口。在下一步中,此实例将暴露给客户端,以便它们可以与服务进行交互。

实现 AIDL 接口时请注意以下几条规则:

  • 传入调用不保证在主线程上执行,因此您需要从一开始就考虑多线程,并正确构建您的服务以实现线程安全。
  • 默认情况下,IPC 调用是同步的。如果您知道服务需要几毫秒以上才能完成请求,请勿从 Activity 的主线程调用它。这可能会导致应用程序挂起,从而导致 Android 显示“应用程序无响应”对话框。请从客户端的单独线程调用它。
  • 只有 Parcel.writeException() 参考文档中列出的异常类型才会发送回调用方。

向客户端公开接口

为服务实现接口后,您需要将其公开给客户端,以便它们可以绑定到它。要公开服务的接口,请扩展 Service 并实现 onBind(),以返回您的实现生成的 Stub 类的实例,如上一节所述。这是一个服务示例,它将 IRemoteService 示例接口公开给客户端。

Kotlin

class RemoteService : Service() {

    override fun onCreate() {
        super.onCreate()
    }

    override fun onBind(intent: Intent): IBinder {
        // Return the interface.
        return binder
    }


    private val binder = object : IRemoteService.Stub() {
        override fun getPid(): Int {
            return Process.myPid()
        }

        override fun basicTypes(
                anInt: Int,
                aLong: Long,
                aBoolean: Boolean,
                aFloat: Float,
                aDouble: Double,
                aString: String
        ) {
            // Does nothing.
        }
    }
}

Java

public class RemoteService extends Service {
    @Override
    public void onCreate() {
        super.onCreate();
    }

    @Override
    public IBinder onBind(Intent intent) {
        // Return the interface.
        return binder;
    }

    private final IRemoteService.Stub binder = new IRemoteService.Stub() {
        public int getPid(){
            return Process.myPid();
        }
        public void basicTypes(int anInt, long aLong, boolean aBoolean,
            float aFloat, double aDouble, String aString) {
            // Does nothing.
        }
    };
}

现在,当客户端(例如 Activity)调用 bindService() 以连接到此服务时,客户端的 onServiceConnected() 回调会收到服务 onBind() 方法返回的 binder 实例。

客户端还必须能够访问接口类。因此,如果客户端和服务位于单独的应用中,则客户端的应用必须在其 src/ 目录中拥有 .aidl 文件的副本,该文件会生成 android.os.Binder 接口,从而为客户端提供对 AIDL 方法的访问权限。

当客户端在 onServiceConnected() 回调中收到 IBinder 时,它必须调用 YourServiceInterface.Stub.asInterface(service) 将返回的参数转换为 YourServiceInterface 类型:

Kotlin

var iRemoteService: IRemoteService? = null

val mConnection = object : ServiceConnection {

    // Called when the connection with the service is established.
    override fun onServiceConnected(className: ComponentName, service: IBinder) {
        // Following the preceding example for an AIDL interface,
        // this gets an instance of the IRemoteInterface, which we can use to call on the service.
        iRemoteService = IRemoteService.Stub.asInterface(service)
    }

    // Called when the connection with the service disconnects unexpectedly.
    override fun onServiceDisconnected(className: ComponentName) {
        Log.e(TAG, "Service has unexpectedly disconnected")
        iRemoteService = null
    }
}

Java

IRemoteService iRemoteService;
private ServiceConnection mConnection = new ServiceConnection() {
    // Called when the connection with the service is established.
    public void onServiceConnected(ComponentName className, IBinder service) {
        // Following the preceding example for an AIDL interface,
        // this gets an instance of the IRemoteInterface, which we can use to call on the service.
        iRemoteService = IRemoteService.Stub.asInterface(service);
    }

    // Called when the connection with the service disconnects unexpectedly.
    public void onServiceDisconnected(ComponentName className) {
        Log.e(TAG, "Service has unexpectedly disconnected");
        iRemoteService = null;
    }
};

有关更多示例代码,请参阅 ApiDemos 中的 RemoteService.java 类。

通过 IPC 传递对象

在 Android 10(API 级别 29 或更高版本)中,您可以在 AIDL 中直接定义 Parcelable 对象。此处也支持作为 AIDL 接口参数和其他 Parcelable 支持的类型。这避免了手动编写编组代码和自定义类的额外工作。然而,这也会创建一个裸结构体。如果需要自定义访问器或其他功能,请改为实现 Parcelable

package android.graphics;

// Declare Rect so AIDL can find it and knows that it implements
// the parcelable protocol.
parcelable Rect {
    int left;
    int top;
    int right;
    int bottom;
}

上述代码示例会自动生成一个带有整数字段 lefttoprightbottom 的 Java 类。所有相关的编组代码都已自动实现,并且可以直接使用该对象,无需添加任何实现。

您还可以通过 IPC 接口将自定义类从一个进程发送到另一个进程。但是,请确保您的类的代码可用于 IPC 通道的另一端,并且您的类必须支持 Parcelable 接口。支持 Parcelable 很重要,因为它允许 Android 系统将对象分解为可以在进程之间编组的基本类型。

要创建支持 Parcelable 的自定义类,请执行以下操作:

  1. 让您的类实现 Parcelable 接口。
  2. 实现 writeToParcel,它接受对象的当前状态并将其写入 Parcel
  3. 在您的类中添加一个名为 CREATOR 的静态字段,该字段是一个实现 Parcelable.Creator 接口的对象。
  4. 最后,创建一个 .aidl 文件来声明您的 Parcelable 类,如以下 Rect.aidl 文件所示。

    如果您使用的是自定义构建过程,请不要.aidl 文件添加到构建中。与 C 语言中的头文件类似,此 .aidl 文件不会被编译。

AIDL 在其生成的代码中使用这些方法和字段来编组和解组您的对象。

例如,这是一个 Rect.aidl 文件,用于创建一个可 Parcelable 的 Rect 类:

package android.graphics;

// Declare Rect so AIDL can find it and knows that it implements
// the parcelable protocol.
parcelable Rect;

以下是 Rect 类如何实现 Parcelable 协议的示例。

Kotlin

import android.os.Parcel
import android.os.Parcelable

class Rect() : Parcelable {
    var left: Int = 0
    var top: Int = 0
    var right: Int = 0
    var bottom: Int = 0

    companion object CREATOR : Parcelable.Creator<Rect> {
        override fun createFromParcel(parcel: Parcel): Rect {
            return Rect(parcel)
        }

        override fun newArray(size: Int): Array<Rect?> {
            return Array(size) { null }
        }
    }

    private constructor(inParcel: Parcel) : this() {
        readFromParcel(inParcel)
    }

    override fun writeToParcel(outParcel: Parcel, flags: Int) {
        outParcel.writeInt(left)
        outParcel.writeInt(top)
        outParcel.writeInt(right)
        outParcel.writeInt(bottom)
    }

    private fun readFromParcel(inParcel: Parcel) {
        left = inParcel.readInt()
        top = inParcel.readInt()
        right = inParcel.readInt()
        bottom = inParcel.readInt()
    }

    override fun describeContents(): Int {
        return 0
    }
}

Java

import android.os.Parcel;
import android.os.Parcelable;

public final class Rect implements Parcelable {
    public int left;
    public int top;
    public int right;
    public int bottom;

    public static final Parcelable.Creator<Rect> CREATOR = new Parcelable.Creator<Rect>() {
        public Rect createFromParcel(Parcel in) {
            return new Rect(in);
        }

        public Rect[] newArray(int size) {
            return new Rect[size];
        }
    };

    public Rect() {
    }

    private Rect(Parcel in) {
        readFromParcel(in);
    }

    public void writeToParcel(Parcel out, int flags) {
        out.writeInt(left);
        out.writeInt(top);
        out.writeInt(right);
        out.writeInt(bottom);
    }

    public void readFromParcel(Parcel in) {
        left = in.readInt();
        top = in.readInt();
        right = in.readInt();
        bottom = in.readInt();
    }

    public int describeContents() {
        return 0;
    }
}

Rect 类中的编组很简单。查看 Parcel 上的其他方法,了解您可以写入 Parcel 的其他类型的值。

警告:请记住从其他进程接收数据的安全隐患。在这种情况下,RectParcel 读取四个数字,但您需要确保这些数字在调用方尝试执行的任何操作的可接受值范围内。有关如何保护应用程序免受恶意软件侵害的更多信息,请参阅安全提示

带有包含 Parcelable 的 Bundle 参数的方法

如果方法接受预期包含 Parcelable 的 Bundle 对象,请务必在尝试从 Bundle 读取之前,通过调用 Bundle.setClassLoader(ClassLoader) 来设置 Bundle 的类加载器。否则,即使 Parcelable 在您的应用程序中已正确定义,您也会遇到 ClassNotFoundException

例如,考虑以下 .aidl 文件示例:

// IRectInsideBundle.aidl
package com.example.android;

/** Example service interface */
interface IRectInsideBundle {
    /** Rect parcelable is stored in the bundle with key "rect". */
    void saveRect(in Bundle bundle);
}
如以下实现所示,在读取 Rect 之前,ClassLoader 会在 Bundle 中明确设置:

Kotlin

private val binder = object : IRectInsideBundle.Stub() {
    override fun saveRect(bundle: Bundle) {
      bundle.classLoader = classLoader
      val rect = bundle.getParcelable<Rect>("rect")
      process(rect) // Do more with the parcelable.
    }
}

Java

private final IRectInsideBundle.Stub binder = new IRectInsideBundle.Stub() {
    public void saveRect(Bundle bundle){
        bundle.setClassLoader(getClass().getClassLoader());
        Rect rect = bundle.getParcelable("rect");
        process(rect); // Do more with the parcelable.
    }
};

调用 IPC 方法

要调用通过 AIDL 定义的远程接口,请在调用类中执行以下步骤:

  1. .aidl 文件包含在项目 src/ 目录中。
  2. 声明 IBinder 接口的一个实例,该实例是根据 AIDL 生成的。
  3. 实现 ServiceConnection
  4. 调用 Context.bindService(),传入您的 ServiceConnection 实现。
  5. 在您的 onServiceConnected() 实现中,您会收到一个 IBinder 实例,名为 service。调用 YourInterfaceName.Stub.asInterface((IBinder)service) 将返回的参数转换为 YourInterface 类型。
  6. 调用您在接口上定义的方法。始终捕获 DeadObjectException 异常,当连接断开时会抛出这些异常。此外,捕获 SecurityException 异常,当 IPC 方法调用涉及的两个进程具有冲突的 AIDL 定义时会抛出这些异常。
  7. 要断开连接,请使用接口实例调用 Context.unbindService()

调用 IPC 服务时请记住以下几点:

  • 对象在进程之间是引用计数的。
  • 您可以将匿名对象作为方法参数发送。

有关绑定到服务的更多信息,请阅读绑定服务概览

以下是一些示例代码,演示了如何调用 AIDL 创建的服务,摘自 ApiDemos 项目中的远程服务示例。

Kotlin

private const val BUMP_MSG = 1

class Binding : Activity() {

    /** The primary interface you call on the service.  */
    private var mService: IRemoteService? = null

    /** Another interface you use on the service.  */
    internal var secondaryService: ISecondary? = null

    private lateinit var killButton: Button
    private lateinit var callbackText: TextView
    private lateinit var handler: InternalHandler

    private var isBound: Boolean = false

    /**
     * Class for interacting with the main interface of the service.
     */
    private val mConnection = object : ServiceConnection {

        override fun onServiceConnected(className: ComponentName, service: IBinder) {
            // This is called when the connection with the service is
            // established, giving us the service object we can use to
            // interact with the service.  We are communicating with our
            // service through an IDL interface, so get a client-side
            // representation of that from the raw service object.
            mService = IRemoteService.Stub.asInterface(service)
            killButton.isEnabled = true
            callbackText.text = "Attached."

            // We want to monitor the service for as long as we are
            // connected to it.
            try {
                mService?.registerCallback(mCallback)
            } catch (e: RemoteException) {
                // In this case, the service crashes before we can
                // do anything with it. We can count on soon being
                // disconnected (and then reconnected if it can be restarted)
                // so there is no need to do anything here.
            }

            // As part of the sample, tell the user what happened.
            Toast.makeText(
                    this@Binding,
                    R.string.remote_service_connected,
                    Toast.LENGTH_SHORT
            ).show()
        }

        override fun onServiceDisconnected(className: ComponentName) {
            // This is called when the connection with the service is
            // unexpectedly disconnected&mdash;that is, its process crashed.
            mService = null
            killButton.isEnabled = false
            callbackText.text = "Disconnected."

            // As part of the sample, tell the user what happened.
            Toast.makeText(
                    this@Binding,
                    R.string.remote_service_disconnected,
                    Toast.LENGTH_SHORT
            ).show()
        }
    }

    /**
     * Class for interacting with the secondary interface of the service.
     */
    private val secondaryConnection = object : ServiceConnection {

        override fun onServiceConnected(className: ComponentName, service: IBinder) {
            // Connecting to a secondary interface is the same as any
            // other interface.
            secondaryService = ISecondary.Stub.asInterface(service)
            killButton.isEnabled = true
        }

        override fun onServiceDisconnected(className: ComponentName) {
            secondaryService = null
            killButton.isEnabled = false
        }
    }

    private val mBindListener = View.OnClickListener {
        // Establish a couple connections with the service, binding
        // by interface names. This lets other applications be
        // installed that replace the remote service by implementing
        // the same interface.
        val intent = Intent(this@Binding, RemoteService::class.java)
        intent.action = IRemoteService::class.java.name
        bindService(intent, mConnection, Context.BIND_AUTO_CREATE)
        intent.action = ISecondary::class.java.name
        bindService(intent, secondaryConnection, Context.BIND_AUTO_CREATE)
        isBound = true
        callbackText.text = "Binding."
    }

    private val unbindListener = View.OnClickListener {
        if (isBound) {
            // If we have received the service, and hence registered with
            // it, then now is the time to unregister.
            try {
                mService?.unregisterCallback(mCallback)
            } catch (e: RemoteException) {
                // There is nothing special we need to do if the service
                // crashes.
            }

            // Detach our existing connection.
            unbindService(mConnection)
            unbindService(secondaryConnection)
            killButton.isEnabled = false
            isBound = false
            callbackText.text = "Unbinding."
        }
    }

    private val killListener = View.OnClickListener {
        // To kill the process hosting the service, we need to know its
        // PID.  Conveniently, the service has a call that returns
        // that information.
        try {
            secondaryService?.pid?.also { pid ->
                // Note that, though this API lets us request to
                // kill any process based on its PID, the kernel
                // still imposes standard restrictions on which PIDs you
                // can actually kill. Typically this means only
                // the process running your application and any additional
                // processes created by that app, as shown here. Packages
                // sharing a common UID are also able to kill each
                // other's processes.
                Process.killProcess(pid)
                callbackText.text = "Killed service process."
            }
        } catch (ex: RemoteException) {
            // Recover gracefully from the process hosting the
            // server dying.
            // For purposes of this sample, put up a notification.
            Toast.makeText(this@Binding, R.string.remote_call_failed, Toast.LENGTH_SHORT).show()
        }
    }

    // ----------------------------------------------------------------------
    // Code showing how to deal with callbacks.
    // ----------------------------------------------------------------------

    /**
     * This implementation is used to receive callbacks from the remote
     * service.
     */
    private val mCallback = object : IRemoteServiceCallback.Stub() {
        /**
         * This is called by the remote service regularly to tell us about
         * new values.  Note that IPC calls are dispatched through a thread
         * pool running in each process, so the code executing here is
         * NOT running in our main thread like most other things. So,
         * to update the UI, we need to use a Handler to hop over there.
         */
        override fun valueChanged(value: Int) {
            handler.sendMessage(handler.obtainMessage(BUMP_MSG, value, 0))
        }
    }

    /**
     * Standard initialization of this activity.  Set up the UI, then wait
     * for the user to interact with it before doing anything.
     */
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        setContentView(R.layout.remote_service_binding)

        // Watch for button taps.
        var button: Button = findViewById(R.id.bind)
        button.setOnClickListener(mBindListener)
        button = findViewById(R.id.unbind)
        button.setOnClickListener(unbindListener)
        killButton = findViewById(R.id.kill)
        killButton.setOnClickListener(killListener)
        killButton.isEnabled = false

        callbackText = findViewById(R.id.callback)
        callbackText.text = "Not attached."
        handler = InternalHandler(callbackText)
    }

    private class InternalHandler(
            textView: TextView,
            private val weakTextView: WeakReference<TextView> = WeakReference(textView)
    ) : Handler() {
        override fun handleMessage(msg: Message) {
            when (msg.what) {
                BUMP_MSG -> weakTextView.get()?.text = "Received from service: ${msg.arg1}"
                else -> super.handleMessage(msg)
            }
        }
    }
}

Java

public static class Binding extends Activity {
    /** The primary interface we are calling on the service. */
    IRemoteService mService = null;
    /** Another interface we use on the service. */
    ISecondary secondaryService = null;

    Button killButton;
    TextView callbackText;

    private InternalHandler handler;
    private boolean isBound;

    /**
     * Standard initialization of this activity. Set up the UI, then wait
     * for the user to interact with it before doing anything.
     */
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.remote_service_binding);

        // Watch for button taps.
        Button button = (Button)findViewById(R.id.bind);
        button.setOnClickListener(mBindListener);
        button = (Button)findViewById(R.id.unbind);
        button.setOnClickListener(unbindListener);
        killButton = (Button)findViewById(R.id.kill);
        killButton.setOnClickListener(killListener);
        killButton.setEnabled(false);

        callbackText = (TextView)findViewById(R.id.callback);
        callbackText.setText("Not attached.");
        handler = new InternalHandler(callbackText);
    }

    /**
     * Class for interacting with the main interface of the service.
     */
    private ServiceConnection mConnection = new ServiceConnection() {
        public void onServiceConnected(ComponentName className,
                IBinder service) {
            // This is called when the connection with the service is
            // established, giving us the service object we can use to
            // interact with the service.  We are communicating with our
            // service through an IDL interface, so get a client-side
            // representation of that from the raw service object.
            mService = IRemoteService.Stub.asInterface(service);
            killButton.setEnabled(true);
            callbackText.setText("Attached.");

            // We want to monitor the service for as long as we are
            // connected to it.
            try {
                mService.registerCallback(mCallback);
            } catch (RemoteException e) {
                // In this case the service crashes before we can even
                // do anything with it. We can count on soon being
                // disconnected (and then reconnected if it can be restarted)
                // so there is no need to do anything here.
            }

            // As part of the sample, tell the user what happened.
            Toast.makeText(Binding.this, R.string.remote_service_connected,
                    Toast.LENGTH_SHORT).show();
        }

        public void onServiceDisconnected(ComponentName className) {
            // This is called when the connection with the service is
            // unexpectedly disconnected&mdash;that is, its process crashed.
            mService = null;
            killButton.setEnabled(false);
            callbackText.setText("Disconnected.");

            // As part of the sample, tell the user what happened.
            Toast.makeText(Binding.this, R.string.remote_service_disconnected,
                    Toast.LENGTH_SHORT).show();
        }
    };

    /**
     * Class for interacting with the secondary interface of the service.
     */
    private ServiceConnection secondaryConnection = new ServiceConnection() {
        public void onServiceConnected(ComponentName className,
                IBinder service) {
            // Connecting to a secondary interface is the same as any
            // other interface.
            secondaryService = ISecondary.Stub.asInterface(service);
            killButton.setEnabled(true);
        }

        public void onServiceDisconnected(ComponentName className) {
            secondaryService = null;
            killButton.setEnabled(false);
        }
    };

    private OnClickListener mBindListener = new OnClickListener() {
        public void onClick(View v) {
            // Establish a couple connections with the service, binding
            // by interface names. This lets other applications be
            // installed that replace the remote service by implementing
            // the same interface.
            Intent intent = new Intent(Binding.this, RemoteService.class);
            intent.setAction(IRemoteService.class.getName());
            bindService(intent, mConnection, Context.BIND_AUTO_CREATE);
            intent.setAction(ISecondary.class.getName());
            bindService(intent, secondaryConnection, Context.BIND_AUTO_CREATE);
            isBound = true;
            callbackText.setText("Binding.");
        }
    };

    private OnClickListener unbindListener = new OnClickListener() {
        public void onClick(View v) {
            if (isBound) {
                // If we have received the service, and hence registered with
                // it, then now is the time to unregister.
                if (mService != null) {
                    try {
                        mService.unregisterCallback(mCallback);
                    } catch (RemoteException e) {
                        // There is nothing special we need to do if the service
                        // crashes.
                    }
                }

                // Detach our existing connection.
                unbindService(mConnection);
                unbindService(secondaryConnection);
                killButton.setEnabled(false);
                isBound = false;
                callbackText.setText("Unbinding.");
            }
        }
    };

    private OnClickListener killListener = new OnClickListener() {
        public void onClick(View v) {
            // To kill the process hosting our service, we need to know its
            // PID.  Conveniently, our service has a call that returns
            // that information.
            if (secondaryService != null) {
                try {
                    int pid = secondaryService.getPid();
                    // Note that, though this API lets us request to
                    // kill any process based on its PID, the kernel
                    // still imposes standard restrictions on which PIDs you
                    // can actually kill.  Typically this means only
                    // the process running your application and any additional
                    // processes created by that app as shown here. Packages
                    // sharing a common UID are also able to kill each
                    // other's processes.
                    Process.killProcess(pid);
                    callbackText.setText("Killed service process.");
                } catch (RemoteException ex) {
                    // Recover gracefully from the process hosting the
                    // server dying.
                    // For purposes of this sample, put up a notification.
                    Toast.makeText(Binding.this,
                            R.string.remote_call_failed,
                            Toast.LENGTH_SHORT).show();
                }
            }
        }
    };

    // ----------------------------------------------------------------------
    // Code showing how to deal with callbacks.
    // ----------------------------------------------------------------------

    /**
     * This implementation is used to receive callbacks from the remote
     * service.
     */
    private IRemoteServiceCallback mCallback = new IRemoteServiceCallback.Stub() {
        /**
         * This is called by the remote service regularly to tell us about
         * new values.  Note that IPC calls are dispatched through a thread
         * pool running in each process, so the code executing here is
         * NOT running in our main thread like most other things. So,
         * to update the UI, we need to use a Handler to hop over there.
         */
        public void valueChanged(int value) {
            handler.sendMessage(handler.obtainMessage(BUMP_MSG, value, 0));
        }
    };

    private static final int BUMP_MSG = 1;

    private static class InternalHandler extends Handler {
        private final WeakReference<TextView> weakTextView;

        InternalHandler(TextView textView) {
            weakTextView = new WeakReference<>(textView);
        }

        @Override
        public void handleMessage(Message msg) {
            switch (msg.what) {
                case BUMP_MSG:
                    TextView textView = weakTextView.get();
                    if (textView != null) {
                        textView.setText("Received from service: " + msg.arg1);
                    }
                    break;
                default:
                    super.handleMessage(msg);
            }
        }
    }
}