Android 跨应用共享数据Demo

说明一下

本项目有个问题需要说明一下，就是provider的onCreate()方法会先于Activity的onCreate()方法执行，所以DatabaseTest项目一运行，就会先执行provider的onCreate()方法，创建数据库

前提

本项目在前面DatabaseTest项目的基础上进行更改，首先将MyDatabaseHelper中使用Toast弹出数据库创建成功的提示去掉，因为跨程序访问时我们不能直接使用Toast。然后创建一个内容提供器，在包上单机右键 New->Other->Content Provider

这样就能自动导入相关的<provider>进行注册

<provider
            android:authorities="com.example.databasetest.provider"
            android:name=".DatabaseProvider"
            android:enabled="true"
            android:exported="true"/>

DatabaseProvider 代码

public class DatabaseProvider extends ContentProvider {
    public static final int BOOK_DIR = 0;
    public static final int BOOK_ITEM = 1;
    public static final int CATAGORY_DIR = 2;
    public static final int CATAGORY_ITEM = 3;
    public static final String AUTHORITY = "com.example.databasetest.provider";
    public static UriMatcher uriMatcher;
    private MyDatabaseHelper dbhelper;

    static {
        uriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
        uriMatcher.addURI(AUTHORITY, "book", BOOK_DIR);
        uriMatcher.addURI(AUTHORITY, "book/#", BOOK_ITEM);
        uriMatcher.addURI(AUTHORITY, "catagory", CATAGORY_DIR);
        uriMatcher.addURI(AUTHORITY, "catagory/#", CATAGORY_ITEM);
    }

    public DatabaseProvider() {
    }

    @Override
    public int delete(Uri uri, String selection, String[] selectionArgs) {
        SQLiteDatabase db = dbhelper.getWritableDatabase();
        int deletedRows = 0;
        switch (uriMatcher.match(uri)) {
            case BOOK_DIR:
                deletedRows = db.delete("Book", selection, selectionArgs);
                break;
            case BOOK_ITEM:
                String bookId = uri.getPathSegments().get(1);
                deletedRows = db.delete("Book", "id = ?", new String[]{bookId});
                break;
            case CATAGORY_DIR:
                deletedRows = db.delete("Category", selection, selectionArgs);
                break;
            case CATAGORY_ITEM:
                String categoryId = uri.getPathSegments().get(1);
                deletedRows = db.delete("Category", "id = ?", new String[]{categoryId});
                break;
            default:
                break;
        }
        return deletedRows;
    }

    @Override
    public String getType(Uri uri) {
        switch (uriMatcher.match(uri)){
            case BOOK_DIR:
                return "vnd.android.cursor.dir/vnd.com.example.databasetest.provider.book";
            case BOOK_ITEM:
                return "vnd.android.cursor.item/vnd.com.example.databasetest.provider.book";
            case CATAGORY_DIR:
                return "vnd.android.cursor.dir/vnd.com.example.databasetest.provider.category";
            case CATAGORY_ITEM:
                return "vnd.android.cursor.item/vnd.com.example.databasetest.provider.categoty";
        }
        return null;
    }

    @Override
    public Uri insert(Uri uri, ContentValues values) {
        SQLiteDatabase db = dbhelper.getWritableDatabase();
        Uri uriReturn = null;
        switch (uriMatcher.match(uri)) {
            case BOOK_DIR:
            case BOOK_ITEM:
                long newBookId = db.insert("Book", null, values);
                uriReturn = Uri.parse("content://" + AUTHORITY + "/book/" + newBookId);
                break;
            case CATAGORY_DIR:
            case CATAGORY_ITEM:
                long newCategoryId = db.insert("Category", null, values);
                uriReturn = Uri.parse("content://" + AUTHORITY + "/book/" + newCategoryId);
                break;
            default:
                break;
        }
        return uriReturn;
    }

  //应用一运行 provider注册 会先执行该方法 来创建数据库
    @Override
    public boolean onCreate() {
        dbhelper = new MyDatabaseHelper(getContext(), "BookStore.db", null, 2);
        return true;
    }

    @Override
    public Cursor query(Uri uri, String[] projection, String selection,
                        String[] selectionArgs, String sortOrder) {
        SQLiteDatabase db = dbhelper.getReadableDatabase();
        Cursor cursor = null;
        switch (uriMatcher.match(uri)) {
            case BOOK_DIR:
                cursor = db.query("Book", projection, selection, selectionArgs, null, null, sortOrder);
                break;
            case BOOK_ITEM:
                String bookId = uri.getPathSegments().get(1);
                cursor = db.query("Book", projection, "id = ?", new String[]{bookId}, null, null, sortOrder);
                break;
            case CATAGORY_DIR:
                cursor = db.query("Category", projection, selection, selectionArgs, null, null, sortOrder);
                break;
            case CATAGORY_ITEM:
                String categoryId = uri.getPathSegments().get(1);
                cursor = db.query("Category", projection, "id = ?", new String[]{categoryId}, null, null, sortOrder);
                break;
            default:
                break;
        }
        return cursor;
    }

    @Override
    public int update(Uri uri, ContentValues values, String selection,
                      String[] selectionArgs) {
        SQLiteDatabase db = dbhelper.getWritableDatabase();
        int updateRows = 0;
        switch (uriMatcher.match(uri)) {
            case BOOK_DIR:
                updateRows = db.update("Book", values, selection, selectionArgs);
                break;
            case BOOK_ITEM:
                String bookId = uri.getPathSegments().get(1);
                updateRows = db.update("Book", values, "id = ?", new String[]{bookId});
                break;
            case CATAGORY_DIR:
                updateRows = db.update("Category", values, selection, selectionArgs);
                break;
            case CATAGORY_ITEM:
                String categoryId = uri.getPathSegments().get(1);
                updateRows = db.update("Categoty", values, "id = ?", new String[]{categoryId});
                break;
            default:
                break;
        }
        return updateRows;
    }
}

几个注意点

• onCreate()中借用MyDataBaseHelper完成数据库的创建或升级，并且provider的onCreate()方法会先于Activity的onCreate()方法执行
• query()返回cursor
• insert()返回能够表示这条新增数据的URI
• update()和delete()返回受影响的行数
• getPathSegments()会将内容URI权限之后的部分用/分割，并把结果放到字符串列表当中，其第0个位置放的是路径，第1个位置就是id了。

跨应用访问数据

接着在模拟器卸载重装当前应用，再创建一个新项目：ProviderTest

1.布局

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="向 Book 表添加数据"
        android:id="@+id/insert"/>
    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="查询 Book 表中的数据"
        android:id="@+id/query"/>
    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/update"
        android:text="修改 Book 表中的数据"/>
    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/delete"
        android:text="删除 Book 表中的数据"/>

</LinearLayout>

2.主活动

public class MainActivity extends AppCompatActivity {
    private static final String TAG = "MainActivity";
    private String newId;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Button button_insert = findViewById(R.id.insert);
        button_insert.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Uri uri = Uri.parse("content://com.example.databasetest.provider/book");
                ContentValues values = new ContentValues();
                values.put("name","老人与海");
                values.put("author", "海明威");
                values.put("pages",345);
                values.put("price",10.88);
                Uri newUri = getContentResolver().insert(uri, values);
                newId = newUri.getPathSegments().get(1);
            }
        });

        Button button_delete = findViewById(R.id.delete);
        button_delete.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Uri uri = Uri.parse("content://com.example.databasetest.provider/book/"+newId);
                getContentResolver().delete(uri, null, null);
            }
        });
        
        Button button_update = findViewById(R.id.update);
        button_update.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Uri uri = Uri.parse("content://com.example.databasetest.provider/book/"+newId);
                ContentValues values = new ContentValues();
                values.put("name", "绿野仙踪");
                values.put("pages", 666);
                values.put("price", 88.88);
                getContentResolver().update(uri, values, null, null);
            }
        });
        
        Button button_query = findViewById(R.id.query);
        button_query.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Uri uri = Uri.parse("content://com.example.databasetest.provider/book");
                Cursor cursor = getContentResolver().query(uri, null, null, null,null);
                if(cursor != null){
                    while (cursor.moveToNext()){
                        String name = cursor.getString(cursor.getColumnIndex("name"));
                        String author = cursor.getString(cursor.getColumnIndex("author"));
                        int pages = cursor.getInt(cursor.getColumnIndex("pages"));
                        double price = cursor.getDouble(cursor.getColumnIndex("price"));

                        Log.d(TAG, "书名："+name);
                        Log.d(TAG, "作者："+author);
                        Log.d(TAG, "页数："+pages);
                        Log.d(TAG, "价格："+price);
                    }
                }
            }
        });
    }
}

运行：