AIDL源碼解析in、out和inout

爲什麼會想寫這篇文章，只因爲一個error idl.exe E 4928 5836 type_namespace.cpp:130] 'Book' can be an out type, so you must declare it as in, out or inout. 看過上一篇文章Android：IPC之AIDL的學習和總結的同學都知道這是因爲在AIDL文件中使用非常規類型作爲參數傳遞的時候沒有標記指向tag。

介紹

官網介紹AIDL的時候上有這麼一段話

All non-primitive parameters require a directional tag indicating which way the data goes. Either in, out, or inout (see the example below).

Primitives are in by default, and cannot be otherwise.

Caution: You should limit the direction to what is truly needed, because marshalling parameters is expensive.

大概意思是非默認類型的參數都需要添加指向標籤in，out或inout。根據自己的需求去添加，因爲實現是有代價的。

已知結論

看過Android：IPC之AIDL的學習和總結的同學都知道：

in表示輸入型參數（Server可以獲取到Client傳遞過去的數據，但是不能對Client端的數據進行修改）

out表示輸出型參數（Server獲取不到Client傳遞過去的數據，但是能對Client端的數據進行修改）

inout表示輸入輸出型參數（Server可以獲取到Client傳遞過去的數據，但是能對Client端的數據進行修改）。

提出問題

下邊我們就研究一個in，out或inout爲什麼能代表不同的傳輸方式，爲什麼實現的代價不一樣。

過程驗證

創建Book.aidl文件

package com.tzx.aidldemo.aidl;
parcelable Book;

創建Book.java文件

package com.tzx.aidldemo.aidl;
public class Book implements Parcelable {
    public int bookId;
    public String bookName;

    public Book() {
    }

    public Book(int bookId, String bookName) {
        this.bookId = bookId;
        this.bookName = bookName;
    }
    //從序列化後的對象中創建原始對象
    protected Book(Parcel in) {
        bookId = in.readInt();
        bookName = in.readString();
    }

    public static final Creator<Book> CREATOR = new Creator<Book>() {
        //從序列化後的對象中創建原始對象
        @Override
        public Book createFromParcel(Parcel in) {
            return new Book(in);
        }
        //指定長度的原始對象數組
        @Override
        public Book[] newArray(int size) {
            return new Book[size];
        }
    };
    //返回當前對象的內容描述。如果含有文件描述符，返回1，否則返回0，幾乎所有情況都返回0
    @Override
    public int describeContents() {
        return 0;
    }
    //將當前對象寫入序列化結構中，其flags標識有兩種（1|0）。
    //爲1時標識當前對象需要作爲返回值返回，不能立即釋放資源，幾乎所有情況下都爲0.
    @Override
    public void writeToParcel(Parcel dest, int flags) {
        dest.writeInt(bookId);
        dest.writeString(bookName);
    }

    @Override
    public String toString() {
        return "[bookId=" + bookId + ",bookName='" + bookName + "']";
    }
}

創建aidl接口文件IBookManager.aidl文件

package com.tzx.aidlinout.aidl;
import com.tzx.aidlinout.aidl.Book;
interface IBookManager {
    Book addInBook(in Book book);
    Book addOutBook(out Book book);
    Book addInoutBook(inout Book book);
}

創建遠程服務

//將bookId都改爲-1，在bookName後面都添加參數的tag標記
public class BookManagerService extends Service {
    private CopyOnWriteArrayList list = new CopyOnWriteArrayList();
    private IBinder mBinder = new IBookManager.Stub(){

        @Override
        public Book addInBook(Book book) throws RemoteException {
            book.bookId = -1;
            book.bookName = book.bookName + "-in";
            list.add(book);
            return book;
        }

        @Override
        public Book addOutBook(Book book) throws RemoteException {
            book.bookId = -1;
            book.bookName = book.bookName + "-out";
            list.add(book);
            return book;
        }

        @Override
        public Book addInoutBook(Book book) throws RemoteException {
            book.bookId = -1;
            book.bookName = book.bookName + "-inout";
            list.add(book);
            return book;
        }

        @Override
        public List<Book> getBookList() throws RemoteException {
            return list;
        }
    };
    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        return mBinder;
    }
}

在創建上面的文件的過程中，遇到不太清楚的或者編譯出現Error的，可以參考Android：IPC之AIDL的學習和總結。

具體方法調用的Activity就不寫全部代碼了，我們看看三種方法的調用

@Override
    public void onClick(View v) {
        switch (v.getId()) {
            case R.id.book_in:
                try {
                    int bookId = Integer.parseInt(bookIdET.getText().toString());
                    String bookName = bookNameET.getText().toString();
                    if (bookId <= 0 || TextUtils.isEmpty(bookName)) return;
                    StringBuilder builder = new StringBuilder();
                    //LogUtils.d("-----------book_in-----------------");
                    Book book0 = new Book(bookId, bookName);
                    String source = "source:" + book0.toString();
                    //LogUtils.d(source);
                    builder.append(source);
                    builder.append('\n');
                    String result = "result:" + bookManager.addInBook(book0).toString();
                    //LogUtils.d(result);
                    builder.append(result);
                    builder.append('\n');
                    source = "source" + book0.toString();
                    //LogUtils.d(source);
                    builder.append(source);
                    //LogUtils.d("**************book_in****************");
                    bookinfoTV.setText(builder.toString());
                } catch (Exception e) {
                    e.printStackTrace();
                }
                break;
            case R.id.book_out:
                try {
                    int bookId = Integer.parseInt(bookIdET.getText().toString());
                    String bookName = bookNameET.getText().toString();
                    if (bookId <= 0 || TextUtils.isEmpty(bookName)) return;
                    StringBuilder builder = new StringBuilder();
                    //LogUtils.d("-----------book_out-----------------");
                    Book book0 = new Book(bookId, bookName);
                    String source = "source:" + book0.toString();
                    //LogUtils.d(source);
                    builder.append(source);
                    builder.append('\n');
                    String result = "result:" + bookManager.addOutBook(book0).toString();
                    //LogUtils.d(result);
                    builder.append(result);
                    builder.append('\n');
                    source = "source" + book0.toString();
                    //LogUtils.d(source);
                    builder.append(source);
                    //LogUtils.d("**************book_out****************");
                    bookinfoTV.setText(builder.toString());
                } catch (Exception e) {
                    e.printStackTrace();
                }
                break;
            case R.id.book_inout:
                try {
                    int bookId = Integer.parseInt(bookIdET.getText().toString());
                    String bookName = bookNameET.getText().toString();
                    if (bookId <= 0 || TextUtils.isEmpty(bookName)) return;
                    StringBuilder builder = new StringBuilder();
                    //LogUtils.d("-----------book_inout-----------------");
                    Book book0 = new Book(bookId, bookName);
                    String source = "source:" + book0.toString();
                    //LogUtils.d(source);
                    builder.append(source);
                    builder.append('\n');
                    String result = "result:" + bookManager.addInoutBook(book0).toString();
                    //LogUtils.d(result);
                    builder.append(result);
                    builder.append('\n');
                    source = "source" + book0.toString();
                    //LogUtils.d(source);
                    builder.append(source);
                    //LogUtils.d("**************book_inout****************");
                    bookinfoTV.setText(builder.toString());
                } catch (Exception e) {
                    e.printStackTrace();
                }
                break;
        }
    }

創建好上面三個文件後，我們編譯整個項目工程（PS：生成aidl接口實現類）。

運行結果

下邊是與結果相對應的Log輸出

14962-14962/com.tzx.aidlinout D/xxx: -----------book_in-----------------
14962-14962/com.tzx.aidlinout D/xxx: source:[bookId=1212,bookName=C++]
14962-14962/com.tzx.aidlinout D/xxx: result:[bookId=-1,bookName=C++-in]
14962-14962/com.tzx.aidlinout D/xxx: source[bookId=1212,bookName=C++]
14962-14962/com.tzx.aidlinout D/xxx: **************book_in****************
14962-14962/com.tzx.aidlinout D/xxx: -----------book_out-----------------
14962-14962/com.tzx.aidlinout D/xxx: source:[bookId=1212,bookName=C++]
14962-14962/com.tzx.aidlinout D/xxx: result:[bookId=-1,bookName=null-out]
14962-14962/com.tzx.aidlinout D/xxx: source[bookId=-1,bookName=null-out]
14962-14962/com.tzx.aidlinout D/xxx: **************book_out****************
14962-14962/com.tzx.aidlinout D/xxx: -----------book_inout-----------------
14962-14962/com.tzx.aidlinout D/xxx: source:[bookId=1212,bookName=C++]
14962-14962/com.tzx.aidlinout D/xxx: result:[bookId=-1,bookName=C++-inout]
14962-14962/com.tzx.aidlinout D/xxx: source[bookId=-1,bookName=C++-inout]
14962-14962/com.tzx.aidlinout D/xxx: **************book_inout****************

實際結果與我們已知結論一致~！~！

但問題我們還沒有解決，我們繼續看代碼，其實所有的實現都是在改接口實現類中IBookManager.java

package com.tzx.aidlinout.aidl;
public interface IBookManager extends android.os.IInterface {
    public com.tzx.aidlinout.aidl.Book addInBook(
        com.tzx.aidlinout.aidl.Book book) throws android.os.RemoteException;

    public com.tzx.aidlinout.aidl.Book addOutBook(
        com.tzx.aidlinout.aidl.Book book) throws android.os.RemoteException;

    public com.tzx.aidlinout.aidl.Book addInoutBook(
        com.tzx.aidlinout.aidl.Book book) throws android.os.RemoteException;

    public java.util.List<com.tzx.aidlinout.aidl.Book> getBookList()
        throws android.os.RemoteException;

    /** Local-side IPC implementation stub class. */
    public static abstract class Stub extends android.os.Binder implements com.tzx.aidlinout.aidl.IBookManager {
        private static final java.lang.String DESCRIPTOR = "com.tzx.aidlinout.aidl.IBookManager";
        static final int TRANSACTION_addInBook = (android.os.IBinder.FIRST_CALL_TRANSACTION +
            0);
        static final int TRANSACTION_addOutBook = (android.os.IBinder.FIRST_CALL_TRANSACTION +
            1);
        static final int TRANSACTION_addInoutBook = (android.os.IBinder.FIRST_CALL_TRANSACTION +
            2);
        static final int TRANSACTION_getBookList = (android.os.IBinder.FIRST_CALL_TRANSACTION +
            3);

        /** Construct the stub at attach it to the interface. */
        public Stub() {
            this.attachInterface(this, DESCRIPTOR);
        }

        /**
         * Cast an IBinder object into an com.tzx.aidlinout.aidl.IBookManager interface,
         * generating a proxy if needed.
         */
        public static com.tzx.aidlinout.aidl.IBookManager asInterface(
            android.os.IBinder obj) {
            if ((obj == null)) {
                return null;
            }

            android.os.IInterface iin = obj.queryLocalInterface(DESCRIPTOR);

            if (((iin != null) &&
                    (iin instanceof com.tzx.aidlinout.aidl.IBookManager))) {
                return ((com.tzx.aidlinout.aidl.IBookManager) iin);
            }

            return new com.tzx.aidlinout.aidl.IBookManager.Stub.Proxy(obj);
        }

        @Override
        public android.os.IBinder asBinder() {
            return this;
        }

        @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_addInBook: {
                data.enforceInterface(DESCRIPTOR);
                //聲明輸入的參數_arg0的引用
                com.tzx.aidlinout.aidl.Book _arg0;
                //並根據輸入的數據爲其創建對象
                if ((0 != data.readInt())) {
                    _arg0 = com.tzx.aidlinout.aidl.Book.CREATOR.createFromParcel(data);
                } else {
                    _arg0 = null;
                }
                //獲取調用this.addInBook方法返回的_result
                com.tzx.aidlinout.aidl.Book _result = this.addInBook(_arg0);
                reply.writeNoException();
                //並向reply中寫入返回值_result
                if ((_result != null)) {
                    reply.writeInt(1);
                    _result.writeToParcel(reply,
                        android.os.Parcelable.PARCELABLE_WRITE_RETURN_VALUE);
                } else {
                    reply.writeInt(0);
                }

                return true;
            }

            case TRANSACTION_addOutBook: {
                data.enforceInterface(DESCRIPTOR);
                //聲明輸入的參數_arg0的引用
                com.tzx.aidlinout.aidl.Book _arg0;
                //併爲其創建新的對象
                _arg0 = new com.tzx.aidlinout.aidl.Book();
                //獲取調用this.addOutBook方法返回的_result
                com.tzx.aidlinout.aidl.Book _result = this.addOutBook(_arg0);
                reply.writeNoException();
                //並向reply中寫入返回值_result
                if ((_result != null)) {
                    reply.writeInt(1);
                    _result.writeToParcel(reply,
                        android.os.Parcelable.PARCELABLE_WRITE_RETURN_VALUE);
                } else {
                    reply.writeInt(0);
                }
                //再將參數_arg0寫入reply中，至於爲什麼寫入，我們看看客戶端Proxy中的讀取
                if ((_arg0 != null)) {
                    reply.writeInt(1);
                    _arg0.writeToParcel(reply,
                        android.os.Parcelable.PARCELABLE_WRITE_RETURN_VALUE);
                } else {
                    reply.writeInt(0);
                }

                return true;
            }

            case TRANSACTION_addInoutBook: {
                data.enforceInterface(DESCRIPTOR);
                //聲明輸入的參數_arg0的引用
                com.tzx.aidlinout.aidl.Book _arg0;
                //並根據輸入的數據爲其創建對象
                if ((0 != data.readInt())) {
                    _arg0 = com.tzx.aidlinout.aidl.Book.CREATOR.createFromParcel(data);
                } else {
                    _arg0 = null;
                }
                //獲取調用this.addInoutBook方法返回的_result
                com.tzx.aidlinout.aidl.Book _result = this.addInoutBook(_arg0);
                reply.writeNoException();
                //並向reply中寫入返回值_result
                if ((_result != null)) {
                    reply.writeInt(1);
                    _result.writeToParcel(reply,
                        android.os.Parcelable.PARCELABLE_WRITE_RETURN_VALUE);
                } else {
                    reply.writeInt(0);
                }
                //再將參數_arg0寫入reply中，至於爲什麼寫入，我們看看客戶端Proxy中的讀取
                if ((_arg0 != null)) {
                    reply.writeInt(1);
                    _arg0.writeToParcel(reply,
                        android.os.Parcelable.PARCELABLE_WRITE_RETURN_VALUE);
                } else {
                    reply.writeInt(0);
                }

                return true;
            }

            case TRANSACTION_getBookList: {
                data.enforceInterface(DESCRIPTOR);

                java.util.List<com.tzx.aidlinout.aidl.Book> _result = this.getBookList();
                reply.writeNoException();
                reply.writeTypedList(_result);

                return true;
            }
            }

            return super.onTransact(code, data, reply, flags);
        }

        private static class Proxy implements com.tzx.aidlinout.aidl.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;
            }

            @Override
            public com.tzx.aidlinout.aidl.Book addInBook(
                com.tzx.aidlinout.aidl.Book book)
                throws android.os.RemoteException {
                android.os.Parcel _data = android.os.Parcel.obtain();
                android.os.Parcel _reply = android.os.Parcel.obtain();
                com.tzx.aidlinout.aidl.Book _result;

                try {
                    _data.writeInterfaceToken(DESCRIPTOR);
                    //將客戶端調用時傳入的參數寫入_data中
                    if ((book != null)) {
                        _data.writeInt(1);
                        book.writeToParcel(_data, 0);
                    } else {
                        _data.writeInt(0);
                    }
                    //將_data、_reply序列化對象和Stub.TRANSACTION_addInBook指令傳遞到Server端
                    mRemote.transact(Stub.TRANSACTION_addInBook, _data, _reply,
                        0);
                    _reply.readException();
                    //讀取Server端返回的序列化_reply中的對象
                    if ((0 != _reply.readInt())) {
                        _result = com.tzx.aidlinout.aidl.Book.CREATOR.createFromParcel(_reply);
                    } else {
                        _result = null;
                    }
                    //然後直接將_result返回
                    //我們發現整個方法調用期間傳入的對象book只是將數據寫入到Server，它的值進行並沒有任何修改。
                    //總結：in類型的參數，它向服務端傳入數據，但是卻不接受Server返回的值。
                } finally {
                    _reply.recycle();
                    _data.recycle();
                }

                return _result;
            }

            @Override
            public com.tzx.aidlinout.aidl.Book addOutBook(
                com.tzx.aidlinout.aidl.Book book)
                throws android.os.RemoteException {
                android.os.Parcel _data = android.os.Parcel.obtain();
                android.os.Parcel _reply = android.os.Parcel.obtain();
                com.tzx.aidlinout.aidl.Book _result;

                try {
                    _data.writeInterfaceToken(DESCRIPTOR);
                    //將_data、_reply序列化對象和Stub.TRANSACTION_addInBook指令傳遞到Server端
                    //_data和_reply序列化對象並沒有進行寫入
                    mRemote.transact(Stub.TRANSACTION_addOutBook, _data,
                        _reply, 0);
                    _reply.readException();
                    //讀取Server端返回的序列化_reply中的對象，寫入到_result
                    if ((0 != _reply.readInt())) {
                        _result = com.tzx.aidlinout.aidl.Book.CREATOR.createFromParcel(_reply);
                    } else {
                        _result = null;
                    }
                    //讀取Server端返回的序列化_reply中的對象，寫入到傳入的book對象中
                    if ((0 != _reply.readInt())) {
                        book.readFromParcel(_reply);
                    }
                    //然後直接將_result返回
                    //我們發現整個方法調用期間傳入的對象book並沒有將數據寫入到Server，它的值確實是Server返回的。
                    //總結：out類型的參數，它並不向服務端傳入數據，但是卻接受Server返回的值。
                } finally {
                    _reply.recycle();
                    _data.recycle();
                }

                return _result;
            }

            @Override
            public com.tzx.aidlinout.aidl.Book addInoutBook(
                com.tzx.aidlinout.aidl.Book book)
                throws android.os.RemoteException {
                android.os.Parcel _data = android.os.Parcel.obtain();
                android.os.Parcel _reply = android.os.Parcel.obtain();
                com.tzx.aidlinout.aidl.Book _result;

                try {
                    _data.writeInterfaceToken(DESCRIPTOR);
                    //將客戶端調用時傳入的參數寫入_data中
                    if ((book != null)) {
                        _data.writeInt(1);
                        book.writeToParcel(_data, 0);
                    } else {
                        _data.writeInt(0);
                    }
                    //將_data、_reply序列化對象和Stub.TRANSACTION_addInoutBook指令傳遞到Server端
                    mRemote.transact(Stub.TRANSACTION_addInoutBook, _data,
                        _reply, 0);
                    _reply.readException();
                    //讀取Server端返回的序列化_reply中的對象，寫入到_result
                    if ((0 != _reply.readInt())) {
                        _result = com.tzx.aidlinout.aidl.Book.CREATOR.createFromParcel(_reply);
                    } else {
                        _result = null;
                    }
                    //讀取Server端返回的序列化_reply中的對象，寫入到傳入的book對象中
                    if ((0 != _reply.readInt())) {
                        book.readFromParcel(_reply);
                    }
                    //然後直接將_result返回
                    //我們發現整個方法調用期間傳入的對象book將其數據寫入到Server，並且它的值被Server返回的數據修改。
                    //總結：inout類型的參數，它既向服務端傳入數據，也卻接受Server返回的值。
                } finally {
                    _reply.recycle();
                    _data.recycle();
                }

                return _result;
            }

            @Override
            public java.util.List<com.tzx.aidlinout.aidl.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<com.tzx.aidlinout.aidl.Book> _result;

                try {
                    _data.writeInterfaceToken(DESCRIPTOR);
                    mRemote.transact(Stub.TRANSACTION_getBookList, _data,
                        _reply, 0);
                    _reply.readException();
                    _result = _reply.createTypedArrayList(com.tzx.aidlinout.aidl.Book.CREATOR);
                } finally {
                    _reply.recycle();
                    _data.recycle();
                }

                return _result;
            }
        }
    }
}

看了這麼多代碼是不是感覺腦袋大了，沒事接下來一張圖幫你理的清清楚楚的：

經過兩篇文章對aidl的講解，我想你已經把它理解的透透的了，如果還有什麼問題可以給我留言哦~！

GitHubDemo地址

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