IPC机制---04 Android中的IPC通讯方式（E）

╰+哭是因爲堅強的太久メ 2022-08-21 04:09 151阅读 0赞

*  下面介绍一种IPC通讯的另外一种方式ContentProvider，这是Android中提供的专门用于不同应用间进行数据数据共享的方式。和Messenger一样，底层也是基于Binder的，但是，系统已经为我们做了封装，所以使用起来比AIDL简单多了。
 *  系统内置了许多ContentProvider，比如通讯录 短信信息等，要跨进程通信，只需要通过ContentResolver的query update insert和delete方法即可。
 *  下面创建一个BookProvider，继承自ContentProvider并实现六个抽象方法即可：
 *   *  onCreate     代表CP的创建，一般进行初始化工作，运行在主线程，不建议执行耗时操作
     *  query          查询记录，运行在CP的进程中，由外界回调并运行在Binder线程池中
     *  update        更新记录，如上
     *  insert          添加纪录，如上
     *  delete          删除记录，如上
     *  getType      返回一个Uri请求所对应的MIME类型
 *  废话不多说，直接上代码
 *      package com.happy.ipc.cp.server;
        
        import android.os.Parcel;
        import android.os.Parcelable;
        
        /**
         * Created by zhonglq on 2016/3/14.
         */
        public class Book implements Parcelable {
        
            private int id;
            private String name;
        
            public int getId() {
                return id;
            }
        
            public void setId(int id) {
                this.id = id;
            }
        
            public String getName() {
                return name;
            }
        
            public void setName(String name) {
                this.name = name;
            }
        
        
            @Override
            public int describeContents() {
                return 0;
            }
        
            @Override
            public void writeToParcel(Parcel dest, int flags) {
                dest.writeInt(this.id);
                dest.writeString(this.name);
            }
        
            public Book() {
            }
        
            protected Book(Parcel in) {
                this.id = in.readInt();
                this.name = in.readString();
            }
        
            public static final Creator<Book> CREATOR = new Creator<Book>() {
                public Book createFromParcel(Parcel source) {
                    return new Book(source);
                }
        
                public Book[] newArray(int size) {
                    return new Book[size];
                }
            };
        }
    
        package com.happy.ipc.cp.server;
        
        import android.os.Parcel;
        import android.os.Parcelable;
        
        /**
         * Created by zhonglq on 2016/3/14.
         */
        public class User implements Parcelable {
        
            private int id;
            private String name;
        
            public int getId() {
                return id;
            }
        
            public void setId(int id) {
                this.id = id;
            }
        
            public String getName() {
                return name;
            }
        
            public void setName(String name) {
                this.name = name;
            }
        
        
            @Override
            public int describeContents() {
                return 0;
            }
        
            @Override
            public void writeToParcel(Parcel dest, int flags) {
                dest.writeInt(this.id);
                dest.writeString(this.name);
            }
        
            public User() {
            }
        
            protected User(Parcel in) {
                this.id = in.readInt();
                this.name = in.readString();
            }
        
            public static final Creator<User> CREATOR = new Creator<User>() {
                public User createFromParcel(Parcel source) {
                    return new User(source);
                }
        
                public User[] newArray(int size) {
                    return new User[size];
                }
            };
        }
    
        <pre name="code" class="java">package com.happy.ipc.cp.server;
        
        import android.content.Context;
        import android.database.sqlite.SQLiteDatabase;
        import android.database.sqlite.SQLiteOpenHelper;
        
        /**
         * Created by zhonglq on 2016/3/14.
         */
        public class DBOpenHelper extends SQLiteOpenHelper {
        
            private static final String DB_NAME = "demo.db";
            private static final int DB_VERSION = 1;
        
            public static final String BOOK_TABLE = "book";
            public static final String USER_TABLE = "user";
        
            private String CREATE_BOOK_TABLE = "CREATE TABLE IF NOT EXISTS " + BOOK_TABLE + " (" +
                    "_id INTEGER PRIMARY KEY , name TEXT)";
        
            private String CREATE_USER_TABLE = "CREATE TABLE IF NOT EXISTS " + USER_TABLE + " (" +
                    "_id INTEGER PRIMARY KEY , name TEXT)";
        
            public DBOpenHelper(Context context) {
                super(context, DB_NAME, null, DB_VERSION);
            }
        
            @Override
            public void onCreate(SQLiteDatabase db) {
                db.execSQL(CREATE_BOOK_TABLE);
                db.execSQL(CREATE_USER_TABLE);
            }
        
            @Override
            public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        
            }
        }
    
      
    
 *      package com.happy.ipc.cp.server;
        
        import android.content.ContentProvider;
        import android.content.ContentValues;
        import android.content.Context;
        import android.content.UriMatcher;
        import android.database.Cursor;
        import android.database.sqlite.SQLiteDatabase;
        import android.net.Uri;
        import android.support.annotation.Nullable;
        
        /**
         * Created by zhonglq on 2016/3/14.
         */
        public class BookProvider extends ContentProvider {
        
            private static final String AUTHORITY = "com.happy.ipc.cp.server.book.provider";
        
            private static final String TAG = "BookProvider";
        
            private SQLiteDatabase mDB;
        
            private static final int BOOK_CODE = 1;
        
            private static final int USER_CODE = 2;
        
            private Context mContext;
        
            private static UriMatcher mUriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
        
            static {
                mUriMatcher.addURI(AUTHORITY, "book", BOOK_CODE);
                mUriMatcher.addURI(AUTHORITY, "user", USER_CODE);
            }
        
            @Override
            public boolean onCreate() {
                mContext = getContext();
                initDB();
                return false;
            }
        
            private void initDB() {
                mDB = new DBOpenHelper(mContext).getReadableDatabase();
        
                mDB.execSQL("delete from " + DBOpenHelper.BOOK_TABLE);
                mDB.execSQL("delete from " + DBOpenHelper.USER_TABLE);
        
                mDB.execSQL("insert into " + DBOpenHelper.BOOK_TABLE + " values(1,'三国演义') ");
                mDB.execSQL("insert into " + DBOpenHelper.BOOK_TABLE + " values(2,'红楼梦') ");
        
                mDB.execSQL("insert into " + DBOpenHelper.USER_TABLE + " values(1,'旺财') ");
                mDB.execSQL("insert into " + DBOpenHelper.USER_TABLE + " values(2,'小强') ");
        
            }
        
            @Nullable
            @Override
            public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {
                String tableName = getTableName(uri);
                return mDB.query(tableName, projection, selection, selectionArgs, null, null, sortOrder);
            }
        
            @Nullable
            @Override
            public String getType(Uri uri) {
                return null;
            }
        
            @Nullable
            @Override
            public Uri insert(Uri uri, ContentValues values) {
                long insert = mDB.insert(getTableName(uri), null, values);
                if (insert > 0) {
                    mContext.getContentResolver().notifyChange(uri, null);
                }
                return null;
            }
        
            @Override
            public int delete(Uri uri, String selection, String[] selectionArgs) {
                int delete = mDB.delete(getTableName(uri), selection, selectionArgs);
                if (delete > 0) {
                    mContext.getContentResolver().notifyChange(uri, null);
                }
                return delete;
            }
        
            @Override
            public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {
                int update = mDB.update(getTableName(uri), values, selection, selectionArgs);
                if (update > 0) {
                    mContext.getContentResolver().notifyChange(uri, null);
                }
                return update;
            }
        
            private String getTableName(Uri uri) {
                String tableName = null;
                switch (mUriMatcher.match(uri)) {
                    case BOOK_CODE:
                        tableName = DBOpenHelper.BOOK_TABLE;
                        break;
                    case USER_CODE:
                        tableName = DBOpenHelper.USER_TABLE;
                        break;
                    default:
                        throw new IllegalArgumentException("无法识别的URI");
                }
                return tableName;
            }
        
        }
    
    // 客户端代码
    
        package com.happy.ipc.cp.client;
        
        import android.database.Cursor;
        import android.net.Uri;
        import android.support.v7.app.AppCompatActivity;
        import android.os.Bundle;
        import android.util.Log;
        
        public class MainActivity extends AppCompatActivity {
        
            private static final String TAG = "MainActivity";
        
            @Override
            protected void onCreate(Bundle savedInstanceState) {
                super.onCreate(savedInstanceState);
                setContentView(R.layout.activity_main);
        
                //以book查询为例
                Uri uri = Uri.parse("content://com.happy.ipc.cp.server.book.provider/book");
                Cursor cursor = getContentResolver().query(uri, null, null, null, null);
                if (cursor != null && cursor.getCount() > 0) {
                    while (cursor.moveToNext()) {
                        int id = cursor.getInt(0);
                        String bookName = cursor.getString(1);
                        Log.i(TAG, " id = " + id + " ,bookName = " + bookName);
                    }
                    cursor.close();
                }
            }
        }
 *  注意
 *   *  CRUD四个方法是存在多线程并发访问的，因此要做好线程同步
     *  本例中，只有一个SQLiteDatabase，所以不会存在什么问题
     *  SQLiteDatabase内部对数据库的操作时同步处理的，如果多个SQLiteDatebase对象来操作数据库的话，就无法保证线程的同步，因为多个SQLiteDatabase对象之间无法进行线程同步
     *  如果ContentProvider的底层数据是一块内存的话，比如List，在这种情况下同List的遍历 插入 删除操作就需要进行线程同步，否则容易引起并发错误