[《第一行Android代码》读书笔记] 第7章 跨程序共享数据——探究内容提供器

别忘了，还需要在

AndroidManifest.xml

    
    <application
      ...

新建一个类去继承

ContentProvider

class MyProvider extends ContentProvider{
    
    @Override
    public boolean onCreate() {
        return false;
    }
    @Nullable
    @Override
    public Cursor query(@NonNull Uri uri, @Nullable String[] projection, @Nullable String selection, @Nullable String[] selectionArgs, @Nullable String sortOrder) {
        return null;
    }
    
    @Nullable
    @Override
    public String getType(@NonNull Uri uri) {
        return null;
    }
    @Nullable
    @Override
    public Uri insert(@NonNull Uri uri, @Nullable ContentValues values) {
        return null;
    }
    @Override
    public int delete(@NonNull Uri uri, @Nullable String selection, @Nullable String[] selectionArgs) {
        return 0;
    }
    @Override
    public int update(@NonNull Uri uri, @Nullable ContentValues values, @Nullable String selection, @Nullable String[] selectionArgs) {
        return 0;
    }
}

因为所有的CRUD操作都一定要匹配到相应的内容URI格式才能进行的，而我们当然不可能向

UriMatch

打开上一章

DatabaseTest

public class DatabaseProvider extends ContentProvider {
    public static final int BOOK_DIR = 0;
    public static final int BOOK_ITEM = 1;
    public static final int CATEGORY_DIR = 2;
    public static final int CATEGORY_ITEM = 3;
    public static final String AUTHORITY = "com.example.databasetest.provider";
    private 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, "category", CATEGORY_DIR);
        uriMatcher.addURI(AUTHORITY, "category/#", CATEGORY_ITEM);
    }
    public DatabaseProvider() {
    }
    @Override
    public int delete(Uri uri, String selection, String[] selectionArgs) {
        //删除数据
        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 CATEGORY_DIR:
                deletedRows = db.delete("Category", selection, selectionArgs);
                break;
            case CATEGORY_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.dir/vnd.com.example.databasetest.provider.book";
            case CATEGORY_DIR:
                return "vnd.android.cursor.dir/vnd.com.example.databasetest.provider.category";
            case CATEGORY_ITEM:
                return "vnd.android.cursor.dir/vnd.com.example.databasetest.provider.category";
        }
        return null;
    }
    @Override
    public Uri insert(Uri uri, ContentValues values) {
        //添加数据
        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 CATEGORY_DIR:
            case CATEGORY_ITEM:
                long newCategoryId = db.insert("Category", null, values);
                uriReturn = Uri.parse("content://" + AUTHORITY + "/category/" + newCategoryId);
                break;
            default:
                break;
        }
        return uriReturn;
    }
    @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) {
        //查询数据
        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);//将内容URI权限后的部分以“/”进行分割并放入一个字符串列表，第0个位置是路径，第1个位置是id
                cursor = db.query("Book", projection, "id=?", new String[]{bookId}, null, null, sortOrder);
                break;
            case CATEGORY_DIR:
                cursor = db.query("Category", projection, selection, selectionArgs, null, null, sortOrder);
                break;
            case CATEGORY_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) {
        //更新数据
        SQLiteDatabase db = dbHelper.getWritableDatabase();
        int updatedRows = 0;
        switch (uriMatcher.match(uri)) {
            case BOOK_DIR:
                updatedRows = db.update("Book", values, selection, selectionArgs);
                break;
            case BOOK_ITEM:
                String bookId = uri.getPathSegments().get(1);
                updatedRows = db.update("Book", values, "id =?", new String[]{bookId});
                break;
            case CATEGORY_DIR:
                updatedRows = db.update("Category", values, selection, selectionArgs);
                break;
            case CATEGORY_ITEM:
                String categoryId = uri.getPathSegments().get(1);
                db.update("Category", values, "id =?", new String[]{categoryId});
                break;
        }
        return updatedRows;
    }
}

删除并重新安装

DatabaseTest

ProviderTest

activity_main

然后修改

MainActivity

public class MainActivity extends AppCompatActivity {
    private String newId;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button aDDData = findViewById(R.id.add_data);
        addData.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //添加数据
                Uri uri = Uri.parse("content://com.example.databasetest.provider/book");
                ContentValues values = new ContentValues();
                values.put("name", "A Clash of Kings");
                values.put("author", "George Martin");
                values.put("pages", 1040);
                values.put("price", 22.85);
                Uri newUri = getContentResolver().insert(uri, values);
                newId = newUri.getPathSegments().get(1);
            }
        });
        Button queryData = findViewById(R.id.query_data);
        queryData.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //查询数据
                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"));
                        float prices = cursor.getFloat(cursor.getColumnIndex("prices"));
                        Log.d("MainActivity", "book name is " + name);
                        Log.d("MainActivity", "book author is " + author);
                        Log.d("MainActivity", "book pages is " + pages);
                        Log.d("MainActivity", "book prices is " + prices);
                    }
                    cursor.close();
                }
            }
        });
        Button updateData = findViewById(R.id.update_data);
        updateData.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //更新数据
                Uri uri = Uri.parse("content://com.example.databasetest.provider/book/" + newId);
                ContentValues values = new ContentValues();
                values.put("name", "A StORM of SWords");
                values.put("pages", 1216);
                values.put("price", 24.05);
                getContentResolver().update(uri, values, null, null);
            }
        });
        Button deleteData = findViewById(R.id.delete_data);
        updateData.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //删除数据
                Uri uri = Uri.parse("content://com.example.databasetest.provider/book/" + newId);
                getContentResolver().delete(uri, null, null);
            }
        });
    }
}

略

在本章中，我们一开始了解了Android的权限机制，并且学会了如何在6.0以上的系统使用运行时权限，然后又学习了内容提供器的相关内容，以实现跨程序数据共享的功能。