ContentProvider的知识

2018-06-02 本文已影响0人 s1991721

四大组件之一的ContentProvider，主要用于在不同的应用程序之间实现数据的共享。误区：ContentProvider实际并不存储数据，实际存储是在SQLite、SharePreferences或文件等地，它只是对外提供了统一的读写接口。

本想着内容为ContentProvider的使用和源码分析，但发现本人水平有限源码分析变成了源码追踪，本文作为个人的笔记，源码部分还请掠过

简单使用

1、实现ContentProvider，完成数据实际的增删改查操作

/**
 * Created by mr.lin on 2018/5/30.
 * 实际的存储方式为SQLite
 * MyContentProvider
 */
class MyContentProvider : ContentProvider() {

    companion object {
        val AUTHORITY = "com.ljf.contentprovider.MyContentProvider"//授权信息
        val TABLE_USER = 1//路径码  此例为哪张表
        val TABLE_ANIMAL = 2
    }

    lateinit var dbHelper: SQLiteOpenHelper
    lateinit var db: SQLiteDatabase
    lateinit var match: UriMatcher

    override fun insert(uri: Uri, values: ContentValues?): Uri {
        db.insert(getTableName(uri), null, values)
        return uri
    }

    override fun query(uri: Uri, projection: Array<out String>?, selection: String?, selectionArgs: Array<out String>?, sortOrder: String?): Cursor {
        return db.query(getTableName(uri), projection, selection, selectionArgs, null, null, sortOrder)
    }

    override fun onCreate(): Boolean {//回调在Application的onCreate之前
        dbHelper = OpenHelper(context)
        db = dbHelper.writableDatabase
        match = UriMatcher(NO_MATCH)//配置匹配路径
        match.addURI(AUTHORITY, "user", TABLE_USER)
        match.addURI(AUTHORITY, "animal", TABLE_ANIMAL)
        return true
    }

    override fun update(uri: Uri, values: ContentValues?, selection: String?, selectionArgs: Array<out String>?): Int {
        return db.update(getTableName(uri), values, selection, selectionArgs)
    }

    override fun delete(uri: Uri, selection: String?, selectionArgs: Array<out String>?): Int {
        return db.delete(getTableName(uri), selection, selectionArgs)
    }

    override fun getType(uri: Uri?): String {
        return ""
    }

    private fun getTableName(uri: Uri): String {
        when (match.match(uri)) {//根据uri匹配路径
            TABLE_USER -> return "User"
            TABLE_ANIMAL -> return "Animal"
        }
        return ""
    }
}

2、注册

        <provider
            android:name=".MyContentProvider"
            android:authorities="com.ljf.contentprovider.MyContentProvider"//授权信息
            android:exported="true"//是否对外开放
            android:permission="com.ljf.app"//自定义权限 />

3、使用

插入为例
var uri = Uri.parse("content://com.ljf.contentprovider.MyContentProvider/user")
                var value = ContentValues()
                value.put("name", Et1.text.toString())
                value.put("age", Et2.text.toString())
                resultTv.text = contentResolver.insert(uri, value).toString()

完整代码GitHub