参考APIDEMO及http://developer.android.com/guide/components/loaders.html#app

1、Introduced in Android 3.0, loaders make it easy to
asynchronously load data in an activity or fragment. Loaders have these characteristics:

They are available to every Activity and Fragment.

They provide asynchronous loading of data.

They monitor the source of their data and deliver new results when the content changes.

They automatically reconnect to the last loader's cursor when being recreated after a configuration change. Thus, they don't need to re-query their data.

2、重要的类及接口

LoaderManager An abstract class associated with an Activity or Fragment for
managing one or more Loader instances. This
helps an application manage longer-running operations in conjunction with the Activity orFragment lifecycle;
the most common use of this is with a CursorLoader,
however applications are free to write their own loaders for loading other types of data. 



There is only one LoaderManager per
activity or fragment. But aLoaderManager can
have multiple loaders.
LoaderManager.LoaderCallbacks A callback interface for a client to interact with the LoaderManager.
For example, you use the onCreateLoader() callback
method to create a new loader.
Loader An abstract class that performs asynchronous loading of data. This is the base class for a loader. You would typically use CursorLoader,
but you can implement your own subclass. While loaders are active they should monitor the source of their data and deliver new results when the contents change.
AsyncTaskLoader Abstract loader that provides an AsyncTask to
do the work.
CursorLoader A subclass of AsyncTaskLoader that
queries the ContentResolver and
returns a Cursor.
This class implements the Loader protocol
in a standard way for querying cursors, building on AsyncTaskLoader to
perform the cursor query on a background thread so that it does not block the application's UI. Using this loader is the best way to asynchronously load data from a ContentProvider,
instead of performing a managed query through the fragment or activity's APIs.

3、一般在以下情况使用Loader:

This section describes how to use loaders in an Android application. An application that uses loaders typically includes the following:

An Activity or Fragment.

An instance of the LoaderManager.

A CursorLoader to load data backed by a ContentProvider. Alternatively, you can implement your own subclass of Loader or AsyncTaskLoader to load data from some other source.

An implementation for LoaderManager.LoaderCallbacks. This is where you create new loaders and manage your references to existing loaders.

A way of displaying the loader's data, such as a SimpleCursorAdapter.

A data source, such as a ContentProvider, when using a CursorLoader.

4、LoaderManager有一个内部接口LoaderManager.LoaderCallbacks,这个接口定义了以下方法:

onCreateLoader() — Instantiate and return a new Loader for the given ID.

onLoadFinished() — Called when a previously created loader has finished its load.

onLoaderReset() — Called when a previously created loader is being reset, thus making its data unavailable.

一般而言,用户不需要直接对Loader进行操作,而是使用此接口的方法,进行间接控制。





5、Loader的一般操作

(1)使用LoaderManager.initLoader()初始化一个Loader,它将直接调用onCreateLoader()方法。

You typically initialize a Loader within the activity's onCreate() method, or within the fragment's onActivityCreated() method. You do this as follows:

getLoaderManager().initLoader(0, null, this);

The initLoader() call ensures that a loader is initialized and active. It has two possible outcomes:

  • If the loader specified by the ID already exists, the last created loader is reused.
  • If the loader specified by the ID does not exist, initLoader() triggers the LoaderManager.LoaderCallbacks method onCreateLoader(). This is where you implement the code to instantiate and return a new loader.

(2)初始化完成后,直接调用onLoadFinished()

If at the point of this call the caller is in its started state, and the requested loader already exists and has generated its data, then the system calls onLoadFinished() immediately (during initLoader()), so you must be prepared for this to happen.

Loader之一:基本原理的更多相关文章

  1. webpack4.0各个击破(6)—— Loader篇

    webpack作为前端最火的构建工具,是前端自动化工具链最重要的部分,使用门槛较高.本系列是笔者自己的学习记录,比较基础,希望通过问题 + 解决方式的模式,以前端构建中遇到的具体需求为出发点,学习we ...

  2. webpack4.0各个击破(6)—— Loader篇【华为云技术分享】

    版权声明:本文为博主原创文章,遵循CC 4.0 BY-SA版权协议,转载请附上原文出处链接和本声明. 本文链接:https://blog.csdn.net/devcloud/article/detai ...

  3. webpack的loader的原理和实现

    想要实现一个loader,需要首先了解loader的基本原理和用法. 1. 使用 loader是处理模块的解析器. module: { rules: [ { test: /\.css$/, use: ...

  4. Webpack4.0各个击破(6)loader篇

    目录 一. loader综述 二. 如何写一个loader 三. loader的编译器本质 [参考] 一. loader综述 loader是webpack的核心概念之一,它的基本工作流是将一个文件以字 ...

  5. PHP 实现自动加载

    自动载入主要是省去了一个个类去 include 的繁琐,在 new 时动态的去检查并 include 相应的 class 文件. 先上代码: //index.php <?php class Cl ...

  6. Loader之一:基本原理 分类: H1_ANDROID 2013-11-16 10:29 1923人阅读 评论(0) 收藏

    参考APIDEMO及http://developer.android.com/guide/components/loaders.html#app 1.Introduced in Android 3.0 ...

  7. Trusted Execution Technology (TXT) --- 基本原理篇

    版权声明:本文为博主原创文章,未经博主允许不得转载. http://www.cnblogs.com/tsec/p/8409600.html 1. Intel TXT 介绍 TXT是Trusted Ex ...

  8. Webpack 下使用 web workers 及 基本原理 和 应用场景

    _ 阅读目录 一:web workers的基本原理 二:web Workers 的基本用法 三:在webpack中配置 Web Workers 四:Web Worker的应用场景 回到顶部 一:web ...

  9. 揭秘webpack loader

    前言 Loader(加载器) 是 webpack 的核心之一.它用于将不同类型的文件转换为 webpack 可识别的模块.本文将尝试深入探索 webpack 中的 loader,揭秘它的工作原理,以及 ...

随机推荐

  1. 求一无序数组中第n大的数字 - 快速选择算法

    逛别人博客的时候,偶然看到这一算法题,顺便用C++实现了一下. 最朴素的解法就是先对数组进行排序,返回第n个数即可.. 下面代码中用的是快速选择算法(不晓得这名字对不对) #include <v ...

  2. 【04】基础:将采集结果转成Excel

    前面的教程说了,数据抓取完毕之后,数据以xml格式的形式存储在本地文件夹中. 下面简单地说一下如何将保存在本地的XML文件转成Excel格式. 第一步:压缩文件 进入本地DataScraperWork ...

  3. python的时间模块

    python有两个重要的时间模块,分别是time和datetime 先看time模块 表示时间的几种方法: 1)时间元组:time.struct_time(tm_year=2016,   tm_mon ...

  4. 前端MVVM学习之KnockOut(一)

    MVVM理解 MVVM即Model-View-viewModel,是微软WPF和MVP(Model-View-Presenter)结合发展演变过来的一种新型架构框架. MVVM设计模式有以下优点: ( ...

  5. poj 1129 Channel Allocation

    http://poj.org/problem?id=1129 import java.util.*; import java.math.*; public class Main { public st ...

  6. 删除IE缓存中指定的文件

    DeleteUrlCacheEntry 1.文件单元:WinInt VC声明 BOOL DeleteUrlCacheEntry ( LPCTSTR lpszUrlName); 函数功能 删除Cache ...

  7. Json之语法,格式

    JSON 文本格式在语法上与创建 JavaScript 对象的代码相同.由于这种相似性,无需解析器,JavaScript 程序能够使用内建的 eval() 函数,用 JSON 数据来生成原生的 Jav ...

  8. Windows 7下可以使用的各个命令语句+C#打开

    Windows 7下可以使用的各个命令语句:   control.exe /name microsoft.folderoptions 启动资源管理器的 文件夹属性 选项卡 control.exe /n ...

  9. 2014.8.4我出的模拟赛【你的名字叫czy是吧】

    你的名字叫czy是吧 (mynameisczy.pas/.c/.cpp) 尽管czy放了那么多只NTR酋长,也没能拦住黄巨大.黄巨大和czy相遇了…… “你的名字叫czy是吧” “……” “我们来单挑 ...

  10. STL中,迭代器的分类

    五类迭代器如下: 1.输入迭代器:只读,一次传递    为输入迭代器预定义实现只有istream_iterator和istreambuf_iterator,用于从一个输入流istream中读取.一个输 ...