数据存储

一.Android文件读写操作

1. 文件的基本操作。
2.读取Assets与raw文件夹中的数据。
3. 读写内部存储与外部存储。

<strong> String fileName="t.txt";        //1.文件基本操作        File file=new File(Environment.getExternalStorageDirectory(),fileName);        if (!file.exists()) {            try {                file.createNewFile();                LogUtils.e("文件创建成功" + file.getAbsolutePath());                FileOutputStream outputStream=new FileOutputStream(file);                OutputStreamWriter outputStreamWriter=new OutputStreamWriter(outputStream);                outputStreamWriter.write("gst is ok");                outputStreamWriter.flush();                outputStreamWriter.close();                outputStream.close();                LogUtils.e("文件写入成功" + file.getAbsolutePath());            } catch (IOException e) {                e.printStackTrace();            }        }else{            LogUtils.e("文件创建失败");        }        //2.读取Assets中的文件        try {            InputStream inputStream=getResources().getAssets().open("t.txt");            MediaPlayer mediaPlayer=new MediaPlayer();            mediaPlayer.setDataSource(getResources().getAssets().openFd("shot.mp3").getFileDescriptor());            int length=inputStream.available();            byte[] bytes=new byte[length];            inputStream.read(bytes,0,length);            String msg=new String(bytes);            LogUtils.e(msg);        } catch (IOException e) {            e.printStackTrace();        }        //3.读取raw下的文件        try {            InputStream inputStream=getResources().openRawResource(R.raw.t);            int length=inputStream.available();            byte[] bytes=new byte[length];            inputStream.read(bytes,0,length);            String msg=new String(bytes);            LogUtils.e(msg);        } catch (IOException e) {            e.printStackTrace();        }        //4.读取外部存储        if (file.exists()) {            try {                FileInputStream inputStream=new FileInputStream(file);                byte[] bytes=new byte[1024];                int count=0;                StringBuffer buffer=new StringBuffer();                while ((count=inputStream.read(bytes))!=-1){                    buffer.append(new String(bytes,0,count));                }                LogUtils.e("文件读取成功" + buffer);            } catch (IOException e) {                e.printStackTrace();            }        }else{            LogUtils.e("文件不存在");        }</strong>

二.Android读写首选项

SharedPreference是Android系统中轻量级存储数据的一种方式，操作简便快捷，它的本质是基于XML文件存储Key-Value键值对数据，适合存放程序状态的配置信息。

1. SharedPreference的概念与使用
2. PreferenceActivity的操作

<strong><PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android">    <SwitchPreference        android:key="example_switch"        android:title="@string/pref_title_social_recommendations"        android:summary="@string/pref_description_social_recommendations"        android:defaultValue="true" />    <!-- NOTE: EditTextPreference accepts EditText attributes. -->    <!-- NOTE: EditTextPreference's summary should be set to its value by the activity code. -->    <EditTextPreference        android:key="example_text"        android:title="@string/pref_title_display_name"        android:defaultValue="@string/pref_default_display_name"        android:selectAllOnFocus="true"        android:inputType="textCapWords"        android:capitalize="words"        android:singleLine="true"        android:maxLines="1" />    <!-- NOTE: Hide buttons to simplify the UI. Users can touch outside the dialog to         dismiss it. -->    <!-- NOTE: ListPreference's summary should be set to its value by the activity code. -->    <ListPreference        android:key="example_list"        android:title="@string/pref_title_add_friends_to_messages"        android:defaultValue="-1"        android:entries="@array/pref_example_list_titles"        android:entryValues="@array/pref_example_list_values"        android:negativeButtonText="@null"        android:positiveButtonText="@null" />    <CheckBoxPreference        android:title="是否开启"        android:summaryOn="已经开启"        android:summaryOff=""        android:key="checkbox">    </CheckBoxPreference></PreferenceScreen></strong>

三.使用SQLite数据库存储数据

1.使用代码读写SQLite数据库
2.通过界面操作数据库

四.应用间数据传递

1.认识ContentProvider。
2.使用SQLite存储简单的数据和应用间通过ContentProvider通信数据。

五.在Android中操作XML数据

03:44

1.XML数据结构知识。

XML，即可扩展标记语言（Extensible Markup Language），标准通用标记语言的子集，一种用于标记电子文件使其具有结构性的标记语言。它可以用来标记数据、定义数据类型，是一种允许用户对自己的标记语言进行定义的源语言。本课时对XML数据格式进行介绍。

2.在Android中读取XML中的数据。

 public void readXml(View view) {        DocumentBuilderFactory factory=DocumentBuilderFactory.newInstance();        DocumentBuilder builder= null;        StringBuffer buffer=new StringBuffer();        try {            builder = factory.newDocumentBuilder();            Document document=builder.parse(getAssets().open("languages.xml"));            Element element=document.getDocumentElement();            NodeList nodeList=element.getElementsByTagName("lan");            for (int i = 0; i < nodeList.getLength(); i++) {                Element element1= (Element) nodeList.item(i);                buffer.append(element1.getAttribute("id")+"\n");                buffer.append(element1.getElementsByTagName("name").item(0).getTextContent()+"\n");                buffer.append(element1.getElementsByTagName("ide").item(0).getTextContent()+"\n");            }            LogUtils.e(buffer.toString());        } catch (ParserConfigurationException e) {            e.printStackTrace();        } catch (SAXException e) {            e.printStackTrace();        } catch (IOException e) {            e.printStackTrace();        }    }

3.在Android中生成XML数据。

  public void writeXml(View view) {        DocumentBuilderFactory factory=DocumentBuilderFactory.newInstance();        try {            DocumentBuilder builder=factory.newDocumentBuilder();            Document newXml=builder.newDocument();            Element languages=newXml.createElement("languages");            languages.setAttribute("cat", "it");            Element lan1=newXml.createElement("lan");            lan1.setAttribute("id", "1");            Element name1=newXml.createElement("name");            name1.setTextContent("Java");            Element ide1=newXml.createElement("ide");            ide1.setTextContent("Eclipse");            lan1.appendChild(name1);            lan1.appendChild(ide1);            languages.appendChild(lan1);            Element lan2=newXml.createElement("lan");            lan2.setAttribute("id", "2");            Element name2=newXml.createElement("name");            name2.setTextContent("Swift");            Element ide2=newXml.createElement("ide");            ide2.setTextContent("XCode");            lan2.appendChild(name2);            lan2.appendChild(ide2);            languages.appendChild(lan2);            Element lan3=newXml.createElement("lan");            lan3.setAttribute("id", "3");            Element name3=newXml.createElement("name");            name3.setTextContent("C++");            Element ide3=newXml.createElement("ide");            ide3.setTextContent("Visual Studio");            lan3.appendChild(name3);            lan3.appendChild(ide3);            languages.appendChild(lan3);            newXml.appendChild(languages);            TransformerFactory transformerFactory=TransformerFactory.newInstance();            Transformer transformer=transformerFactory.newTransformer();            transformer.setOutputProperty("encoding","utf-8");            transformer.setOutputProperty("version","1.0");            File file=new File(Environment.getExternalStorageDirectory()+File.separator+"languages.xml");            if (!file.exists()){                file.createNewFile();            }            FileOutputStream outputStream=new FileOutputStream(file);            transformer.transform(new DOMSource(newXml),new StreamResult(outputStream));            LogUtils.i("transformer succeed");        } catch (ParserConfigurationException e) {            e.printStackTrace();        } catch (TransformerConfigurationException e) {            e.printStackTrace();        } catch (IOException e) {            e.printStackTrace();        } catch (TransformerException e) {            e.printStackTrace();        }    }

六.在Android中操作JSON数据

1.JSON数据的特点与优势。

JSON：JavaScript 对象表示法（JavaScript Object Notation）。独立于语言和平台，比 XML 更小、更快，更易解析。如今JSON数据已经成为了互联网中大多数数据的传递方式，所以必须要熟练掌握。
2.在Android中加载并解析JSON数据。

  public void readJson(View view){        try {            InputStream inputStream=getAssets().open("test.json");            byte[] bytes=new byte[1024];            int count=0;            StringBuffer buffer=new StringBuffer();            while ((count=inputStream.read(bytes))>0){                buffer.append(new String(bytes,0,count));            }            JSONObject root=new JSONObject(buffer.toString());            LogUtils.i("cat="+root.getString("cat"));            JSONArray jsonArray=root.getJSONArray("people");            for (int i = 0; i < jsonArray.length(); i++) {                JSONObject jsonObject=jsonArray.getJSONObject(i);                LogUtils.i("firstName="+jsonObject.getString("firstName"));                LogUtils.i("lastName="+jsonObject.getString("lastName"));                LogUtils.i("email="+jsonObject.getString("email"));            }        } catch (IOException e) {            e.printStackTrace();        } catch (JSONException e) {            e.printStackTrace();        }    }

3.在Android中生成JSON数据。

 public void writeJson(View view){        try {            JSONObject root=new JSONObject();            root.put("cat","it");            JSONObject people1=new JSONObject();            people1.put("firstName","Brett");            people1.put("lastName","McLaughlin");            people1.put("email","aaaa");            JSONObject people2=new JSONObject();            people2.put("firstName","Brett");            people2.put("lastName","McLaughlin");            people2.put("email","aaaa");            JSONObject people3=new JSONObject();            people3.put("firstName","Brett");            people3.put("lastName","McLaughlin");            people3.put("email","aaaa");            JSONArray jsonArray=new JSONArray();            jsonArray.put(people1);            jsonArray.put(people2);            jsonArray.put(people3);            root.put("people",jsonArray);            File file=new File(Environment.getExternalStorageDirectory()+File.separator+"test.json");            if (!file.exists()){                file.createNewFile();            }            FileOutputStream outputStream=new FileOutputStream(file);            outputStream.write(root.toString().getBytes());            LogUtils.i(root.toString());        } catch (JSONException e) {            e.printStackTrace();        } catch (FileNotFoundException e) {            e.printStackTrace();        } catch (IOException e) {            e.printStackTrace();        }    }