4.21

所花时间（包括上课）：3.5

打码量(行)：500

博客量(篇)：1

了解到知识点：学习contentProvider

 

 import android.content.ContentProvider;

import android.content.ContentUris;

import android.content.ContentValues;

import android.content.Context;

import android.content.UriMatcher;

import android.database.Cursor;

import android.database.SQLException;

import android.database.sqlite.SQLiteDatabase;

import android.database.sqlite.SQLiteOpenHelper;

import android.net.Uri;

import androidx.annotation.NonNull;

import androidx.annotation.Nullable;

 

public class MyContentProvider extends ContentProvider {

 

    // ContentProvider 的 URI 标识

    private static final String AUTHORITY = "com.example.mycontentprovider";

    private static final String PATH = "items";

    public static final Uri CONTENT_URI = Uri.parse("content://" + AUTHORITY + "/" + PATH);

 

    private static final int ITEMS = 1;

    private static final int ITEM_ID = 2;

 

    private static final UriMatcher uriMatcher;

    static {

        uriMatcher = new UriMatcher(UriMatcher.NO_MATCH);

        uriMatcher.addURI(AUTHORITY, PATH, ITEMS);

        uriMatcher.addURI(AUTHORITY, PATH + "/#", ITEM_ID);

    }

 

    private SQLiteDatabase database;

 

    @Override

    public boolean onCreate() {

        // 初始化数据库

        DatabaseHelper dbHelper = new DatabaseHelper(getContext());

        database = dbHelper.getWritableDatabase();

        return database != null;

    }

 

    @Nullable

    @Override

    public Cursor query(@NonNull Uri uri, @Nullable String[] projection, @Nullable String selection, @Nullable String[] selectionArgs, @Nullable String sortOrder) {

        // 处理查询请求

        Cursor cursor;

        switch (uriMatcher.match(uri)) {

            case ITEMS:

                cursor = database.query(DatabaseHelper.TABLE_NAME, projection, selection, selectionArgs, null, null, sortOrder);

                break;

            case ITEM_ID:

                selection = DatabaseHelper.COLUMN_ID + "=?";

                selectionArgs = new String[]{String.valueOf(ContentUris.parseId(uri))};

                cursor = database.query(DatabaseHelper.TABLE_NAME, projection, selection, selectionArgs, null, null, sortOrder);

                break;

            default:

                throw new IllegalArgumentException("未知的 URI: " + uri);

        }

        cursor.setNotificationUri(getContext().getContentResolver(), uri);

        return cursor;

    }

 

    @Nullable

    @Override

    public Uri insert(@NonNull Uri uri, @Nullable ContentValues values) {

        // 处理插入请求

        long rowId = database.insert(DatabaseHelper.TABLE_NAME, null, values);

        if (rowId > 0) {

            Uri newUri = ContentUris.withAppendedId(CONTENT_URI, rowId);

            getContext().getContentResolver().notifyChange(newUri, null);

            return newUri;

        }

        throw new SQLException("插入行失败: " + uri);

    }

 

    @Override

    public int update(@NonNull Uri uri, @Nullable ContentValues values, @Nullable String selection, @Nullable String[] selectionArgs) {

        // 处理更新请求

        int count;

        switch (uriMatcher.match(uri)) {

            case ITEMS:

                count = database.update(DatabaseHelper.TABLE_NAME, values, selection, selectionArgs);

                break;

            case ITEM_ID:

                selection = DatabaseHelper.COLUMN_ID + "=?";

                selectionArgs = new String[]{String.valueOf(ContentUris.parseId(uri))};

                count = database.update(DatabaseHelper.TABLE_NAME, values, selection, selectionArgs);

                break;

            default:

                throw new IllegalArgumentException("未知的 URI: " + uri);

        }

        getContext().getContentResolver().notifyChange(uri, null);

        return count;

    }

 

    @Override

    public int delete(@NonNull Uri uri, @Nullable String selection, @Nullable String[] selectionArgs) {

        // 处理删除请求

        int count;

        switch (uriMatcher.match(uri)) {

            case ITEMS:

                count = database.delete(DatabaseHelper.TABLE_NAME, selection, selectionArgs);

                break;

            case ITEM_ID:

                selection = DatabaseHelper.COLUMN_ID + "=?";

                selectionArgs = new String[]{String.valueOf(ContentUris.parseId(uri))};

                count = database.delete(DatabaseHelper.TABLE_NAME, selection, selectionArgs);

                break;

            default:

                throw new IllegalArgumentException("未知的 URI: " + uri);

        }

        getContext().getContentResolver().notifyChange(uri, null);

        return count;

    }

 

    @Nullable

    @Override

    public String getType(@NonNull Uri uri) {

        // 返回 MIME 类型

        switch (uriMatcher.match(uri)) {

            case ITEMS:

                return "vnd.android.cursor.dir/vnd.com.example.mycontentprovider.items";

            case ITEM_ID:

                return "vnd.android.cursor.item/vnd.com.example.mycontentprovider.items";

            default:

                throw new IllegalArgumentException("未知的 URI: " + uri);

        }

    }

 

    // SQLiteOpenHelper 子类，用于管理数据库创建和版本管理

    private static class DatabaseHelper extends SQLiteOpenHelper {

 

        private static final String DATABASE_NAME = "mydatabase.db";

        private static final int DATABASE_VERSION = 1;

        private static final String TABLE_NAME = "items";

        private static final String COLUMN_ID = "_id";

        private static final String COLUMN_NAME = "name";

        private static final String COLUMN_VALUE = "value";

 

        private static final String CREATE_TABLE = "CREATE TABLE " + TABLE_NAME + " ("

                + COLUMN_ID + " INTEGER PRIMARY KEY AUTOINCREMENT, "

                + COLUMN_NAME + " TEXT NOT NULL, "

                + COLUMN_VALUE + " TEXT NOT NULL);";

 

        public DatabaseHelper(Context context) {

            super(context, DATABASE_NAME, null, DATABASE_VERSION);

        }

 

        @Override

        public void onCreate(SQLiteDatabase db) {

            // 创建数据库表

            db.execSQL(CREATE_TABLE);

        }

 

        @Override

        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

            // 处理数据库升级

            db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);

            onCreate(db);

        }

    }

}

import android.content.ContentValues;

import android.database.Cursor;

import android.net.Uri;

import android.os.Bundle;

import android.view.View;

import android.widget.Button;

import android.widget.TextView;

import androidx.appcompat.app.AppCompatActivity;

 

public class MainActivity extends AppCompatActivity {

 

    private TextView resultTextView;

 

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

 

        resultTextView = findViewById(R.id.result_text_view);

 

        // 获取按钮视图

        Button insertButton = findViewById(R.id.insert_button);

        Button queryButton = findViewById(R.id.query_button);

 

        // 设置插入数据按钮点击监听器

        insertButton.setOnClickListener(new View.OnClickListener() {

            @Override

            public void onClick(View v) {

                insertData();

            }

        });

 

        // 设置查询数据按钮点击监听器

        queryButton.setOnClickListener(new View.OnClickListener() {

            @Override

            public void onClick(View v) {

                queryData();

            }

        });

    }

 

    private void insertData() {

        // 插入数据到 ContentProvider

        ContentValues values = new ContentValues();

        values.put("name", "Example Name");

        values.put("value", "Example Value");

        Uri newUri = getContentResolver().insert(MyContentProvider.CONTENT_URI, values);

        resultTextView.setText("Inserted: " + newUri);

    }

 

    private void queryData() {

        // 从 ContentProvider 查询数据

        Cursor cursor = getContentResolver().query(MyContentProvider.CONTENT_URI, null, null, null, null);

        if (cursor != null) {

            StringBuilder result = new StringBuilder();

            while (cursor.moveToNext()) {

                String name = cursor.getString(cursor.getColumnIndex("name"));

                String value = cursor.getString(cursor.getColumnIndex("value"));

                result.append("Name: ").append(name).append(", Value: ").append(value).append("\n");

            }

            cursor.close();

            resultTextView.setText(result.toString());

        }

    }

}