使用sqlitedatabase完成基础crud-使用dao对数据库操作进行封包-使用content provider实现数据共享

import android.content.ContentProvider
import android.content.ContentValues
import android.database.Cursor
import android.database.sqlite.SQLiteDatabase
import android.net.Uri
 
class MyContentProvider : ContentProvider() {
 
    private lateinit var databaseHelper: DatabaseHelper
    private var readableDatabase: SQLiteDatabase? = null
    private var writableDatabase: SQLiteDatabase? = null
 
    override fun onCreate(): Boolean {
        context?.let {
            databaseHelper = DatabaseHelper(it)
            readableDatabase = databaseHelper.readableDatabase
            writableDatabase = databaseHelper.writableDatabase
        }
        return true
    }
 
    override fun query(uri: Uri, projection: Array<String>?, selection: String?, selectionArgs: Array<String>?, sortOrder: String?): Cursor? {
        // 实现查询逻辑
        return readableDatabase?.query(DatabaseHelper.TABLE_NAME, projection, selection, selectionArgs, null, null, sortOrder)
    }
 
    override fun insert(uri: Uri, values: ContentValues?): Uri? {
        // 实现插入逻辑
        val id = writableDatabase?.insert(DatabaseHelper.TABLE_NAME, null, values)
        return Uri.parse("content://$authority/$id")
    }
 
    override fun update(uri: Uri, values: ContentValues?, selection: String?, selectionArgs: Array<String>?): Int {
        // 实现更新逻辑
        return writableDatabase?.update(DatabaseHelper.TABLE_NAME, values, selection, selectionArgs) ?: 0
    }
 
    override fun delete(uri: Uri, selection: String?, selectionArgs: Array<String>?): Int {
        // 实现删除逻辑
        return writableDatabase?.delete(DatabaseHelper.TABLE_NAME, selection, selectionArgs) ?: 0
    }
 
    override fun getType(uri: Uri): String? {
        // 根据需要返回MIME类型
        return null
    }
 
    companion object {
        const val authority = "com.example.mycontentprovider"
    }
}

这个代码示例展示了如何实现一个简单的ContentProvider，它封装了对SQLite数据库的基本CRUD操作。注意，这里的DatabaseHelper是假定已经实现的SQLiteOpenHelper子类。在实际应用中，你需要根据自己的数据库结构和需求来实现这些方法。