进程间通信学习系列(二)——简单了解Binder机制
2018-01-17 13:15
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进程间通信学习系列(一)——IPC简介
Binder机制太复杂了,本文只是简单的对Binder进行了解。在Android中Binder是一个类,实现了IBinder接口,在Binder机制中还有两个重要角色Binder驱动(在内核中)和ServiceManager,这两部分Android平台已经实现,我们不必关心,当然有兴趣的童鞋可以研究下。本文主要学习了解应用层的Client和Service相关的Binder知识。
Messenge,ContentProvider等底层实现都是AIDL,所以以AIDL的简单实现来学习Binder机制。
需求:图书管理系统中,1.需要查询图书列表;2.添加新书到图书库中。
先看一下目录结构:
首先新建一个Book类,并实现Parcelable序列化接口(Android
Studio一键生成序列化代码插件),如下:
public class Book implements Parcelable { private double price; private long bookId; private String bookName; @Override public int describeContents() { return 0; } @Override public void writeToParcel(Parcel dest, int flags) { dest.writeDouble(this.price); dest.writeLong(this.bookId); dest.writeString(this.bookName); } public Book() { } protected Book(Parcel in) { this.price = in.readDouble(); this.bookId = in.readLong(); this.bookName = in.readString(); } public static final Parcelable.Creator<Book> CREATOR = new Parcelable.Creator<Book>() { @Override public Book createFromParcel(Parcel source) { return new Book(source); } @Override public Book[] newArray(int size) { return new Book[size]; 4000 } }; }新建IBookManager.aidl文件,生命两个接口:
package anyan.com.ipcdemo.aboutaidl; //注意导入Book类(手动导入) import anyan.com.ipcdemo.aboutaidl.Book; interface IBookManager { List<Book> getBookList();//查询图书列表 void addBook(in Book book);//添加新图书 }
因为在IBookManager.aidl文件中使用了非基本数据类型,所以Book类不仅要实现序列化接口,还要新建一个Book.aidl文件(至于为什么,我也不知道),注意这个Book.aidl文件的全路径包名要与Book.java的全路径包名一致,否则编译会报错。内容如下:
package anyan.com.ipcdemo.aboutaidl; parcelable Book;Rebuild project成功后再app/build/generated/source/aidl/debug/包名 目录下回生成一个IBookManager.java文件,这是AS帮我们自动生成的,这里使用了代理模式(可简单了解一下,Java设计模式-代理模式实现及原理)主要分析这里的代码:包含两个接口getBookList()和addBook(),可以看到这两个接口就是我们在IBookManager.aidl文件中所声明的。一个内部类Stub,继承Binder实现IBookManager接口。Stub类里面还有一个内部类Proxy也实现了IBookManager接口,这个就是Stub类(也就是Binder)的代理类。
public interface IBookManager extends android.os.IInterface { /** * Local-side IPC implementation stub class. */ public static abstract class Stub extends android.os.Binder implements anyan.com.ipcdemo.aboutaidl.IBookManager { //Binder的唯一标识,一般用类名表示 private static final java.lang.String DESCRIPTOR = "anyan.com.ipcdemo.aboutaidl.IBookManager"; /** * Construct the stub at attach it to the interface. */ public Stub() { this.attachInterface(this, DESCRIPTOR); } /** * Cast an IBinder object into an anyan.com.ipcdemo.aboutaidl.IBookManager interface, * generating a proxy if needed. * 将IBinder对象转换成IBookManager接口并返回 * 这种转换区分进程,如果是在同一进程,直接返回服务端的Stub对象; * 如果不在同一进程,则返回代理对象Stub.Proxy; */ public static anyan.com.ipcdemo.aboutaidl.IBookManager asInterface(android.os.IBinder obj) { if ((obj == null)) { return null; } android.os.IInterface iin = obj.queryLocalInterface(DESCRIPTOR); if (((iin != null) && (iin instanceof anyan.com.ipcdemo.aboutaidl.IBookManager))) { return ((anyan.com.ipcdemo.aboutaidl.IBookManager) iin); } return new anyan.com.ipcdemo.aboutaidl.IBookManager.Stub.Proxy(obj); } @Override public android.os.IBinder asBinder() { return this; } /** * 该方法在服务端的Binder线程池中执行,注意采用同步方法 * @param code 确定客户端请求的目标方法是哪个 * @param data 目标方法所需参数数据 * @param reply 目标方法返回数据 * @param flags * @return * @throws android.os.RemoteException */ @Override public boolean onTransact(int code, android.os.Parcel data, android.os.Parcel reply, int flags) throws android.os.RemoteException { switch (code) { case INTERFACE_TRANSACTION: { reply.writeString(DESCRIPTOR); return true; } case TRANSACTION_getBookList: { data.enforceInterface(DESCRIPTOR); java.util.List<anyan.com.ipcdemo.aboutaidl.Book> _result = this.getBookList(); reply.writeNoException(); reply.writeTypedList(_result); return true; } case TRANSACTION_addBook: { data.enforceInterface(DESCRIPTOR); anyan.com.ipcdemo.aboutaidl.Book _arg0; if ((0 != data.readInt())) { _arg0 = anyan.com.ipcdemo.aboutaidl.Book.CREATOR.createFromParcel(data); } else { _arg0 = null; } this.addBook(_arg0); reply.writeNoException(); return true; } } return super.onTransact(code, data, reply, flags); } //代理对象 private static class Proxy implements anyan.com.ipcdemo.aboutaidl.IBookManager { private android.os.IBinder mRemote; Proxy(android.os.IBinder remote) { mRemote = remote; } @Override public android.os.IBinder asBinder() { return mRemote; } public java.lang.String getInterfaceDescriptor() { return DESCRIPTOR; } /** * 该方法在客户端执行, * @return * @throws android.os.RemoteException */ @Override public java.util.List<anyan.com.ipcdemo.aboutaidl.Book> getBookList() throws android.os.RemoteException { android.os.Parcel _data = android.os.Parcel.obtain(); android.os.Parcel _reply = android.os.Parcel.obtain(); java.util.List<anyan.com.ipcdemo.aboutaidl.Book> _result; try { _data.writeInterfaceToken(DESCRIPTOR); //调用远程请求,当前线程挂起,服务端OnTransact()方法会被调用, mRemote.transact(Stub.TRANSACTION_getBookList, _data, _reply, 0); //当前线程继续执行,取出结果 _reply.readException(); _result = _reply.createTypedArrayList(anyan.com.ipcdemo.aboutaidl.Book.CREATOR); } finally { _reply.recycle(); _data.recycle(); } return _result; } @Override public void addBook(anyan.com.ipcdemo.aboutaidl.Book book) throws android.os.RemoteException { android.os.Parcel _data = android.os.Parcel.obtain(); android.os.Parcel _reply = android.os.Parcel.obtain(); try { _data.writeInterfaceToken(DESCRIPTOR); if ((book != null)) { _data.writeInt(1); book.writeToParcel(_data, 0); } else { _data.writeInt(0); } mRemote.transact(Stub.TRANSACTION_addBook, _data, _reply, 0); _reply.readException(); } finally { _reply.recycle(); _data.recycle(); } } } //方法的id static final int TRANSACTION_getBookList = (android.os.IBinder.FIRST_CALL_TRANSACTION + 0); static final int TRANSACTION_addBook = (android.os.IBinder.FIRST_CALL_TRANSACTION + 1); } public java.util.List<anyan.com.ipcdemo.aboutaidl.Book> getBookList() throws android.os.RemoteException; public void addBook(anyan.com.ipcdemo.aboutaidl.Book book) throws android.os.RemoteException; }如下图所示:
接着看具体怎么使用,创建一个BookManagerService类:
public class BookService extends Service { public BookService() { } //支持并发读写 private CopyOnWriteArrayList<Book> bookList = new CopyOnWriteArrayList<>(); private IBookManager.Stub binder = new IBookManager.Stub() { @Override public List<Book> getBookList() throws RemoteException { return bookList; } @Override public void addBook(Book book) throws RemoteException { bookList.add(book); } }; @Override public IBinder onBind(Intent intent) { return binder; } }
在Activity中BindService:
public class MainActivity extends AppCompatActivity { private static final String TAG = "MainActivity"; private IBookManager iBookManager; private ServiceConnection conn = new ServiceConnection() { @Override public void onServiceConnected(ComponentName name, IBinder service) { //用到了上面提到了转换方法asInterface,将IBinder转换为接口, //同一进程直接返回Stub对象,不同进程返回Proxy代理类 iBookManager = IBookManager.Stub.asInterface(service); try { service.linkToDeath(deathRecipient, 0); //拿到对象后就可以直接调用方法了 List<Book> bookList = iBookManager.getBookList(); Log.e(TAG, "onServiceConnected: " + bookList); } catch (RemoteException e) { e.printStackTrace(); } } @Override public void onServiceDisconnected(ComponentName name) { } }; //死亡代理,binder死亡时会收到通知,回调binderDied方法 private IBinder.DeathRecipient deathRecipient = new IBinder.DeathRecipient() { @Override public void binderDied() { if (iBookManager == null) return; iBookManager.asBinder().unlinkToDeath(deathRecipient, 0); iBookManager = null; //重新绑定service Intent intent = new Intent(MainActivity.this, BookService.class); bindService(intent, conn, BIND_AUTO_CREATE); } }; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); } public void onClick(View view) { Intent intent = new Intent(this, BookService.class); bindService(intent, conn, BIND_AUTO_CREATE); } }至此,简单的Binder机制分析完了,看着可能有点懵,很正常,我是看了好几篇才只是简单的理解了。Fighting !!!
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