SharedPreferences的简单使用以及官方API给出的使用方法

Android的四种数据存储方式：
1.SharedPreferences
2.SQLite
3.Content Provider
4.File

今天介绍的是SharedPreferences:

1.是一种轻型的数据存储方式
2.本质是基于XML文件存储key-value键值对数据

3.通常用来存储一些简单的配置信息

为了使用SharedPreferences，写了一个小案例“用户账号登录信息的存储”

首先贴出代码：

package com.example.sharedprefsdemo;import android.app.Activity;import android.content.SharedPreferences;import android.content.SharedPreferences.Editor;import android.os.Bundle;import android.support.v4.widget.SearchViewCompat.OnCloseListenerCompat;import android.view.View;import android.view.View.OnClickListener;import android.widget.Button;import android.widget.CheckBox;import android.widget.EditText;import android.widget.Toast;public class MainActivity extends Activity {private EditText mUserName, mPssWord;private CheckBox mCheck;private Button mLogin, mCancel;private Editor editor;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);initComponent();/** * 1.获得SharedPreferences对象 * 2.通过preferences.edit()获得Editor对象 * 3.通过Editor对象配置文件里写入信息 * 4.写完或者修改完信息后一定要commit */SharedPreferences preferences = getSharedPreferences("user_info",MODE_PRIVATE);editor = preferences.edit();String usrName = preferences.getString("USER_NAME", "");String pssWord = preferences.getString("PASSWORD", "");if ( usrName != null) {mUserName.setText(usrName);}if ( pssWord != null) {mCheck.setChecked(true);mPssWord.setText(pssWord);}}/* * 初始化组件 */private void initComponent() {mUserName = (EditText) findViewById(R.id.username);mPssWord = (EditText) findViewById(R.id.psswd);mCheck = (CheckBox) findViewById(R.id.check);mLogin = (Button) findViewById(R.id.login);mCancel = (Button) findViewById(R.id.cancel);mLogin.setOnClickListener(new MyListener());mCancel.setOnClickListener(new MyListener());}class MyListener implements OnClickListener {@Overridepublic void onClick(View v) {String userName = mUserName.getText().toString().trim();String pssWord = mPssWord.getText().toString().trim();if (v.getId() == R.id.login) {if (userName.equals("admin") && pssWord.equals("123456")) {if (mCheck.isChecked()) {// 写入信息editor.putString("USER_NAME", userName);editor.putString("PASSWORD", pssWord);editor.commit();}else{// 移除信息editor.remove("PASSWORD");editor.commit();}Toast.makeText(MainActivity.this, "成功登陆！", 0).show();}else{Toast.makeText(MainActivity.this, "账户信息有误，请重新输入！", 0).show();}}}}}

布局文件代码：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:layout_margin="5dp"    android:orientation="vertical"    tools:context="${relativePackage}.${activityClass}" >    <LinearLayout        android:layout_width="match_parent"        android:layout_height="wrap_content"        android:orientation="horizontal" >        <TextView            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:text="@string/_username"            android:textSize="18sp" />        <EditText            android:id="@+id/username"            android:layout_width="match_parent"            android:layout_height="wrap_content"            android:singleLine="true" >        </EditText>    </LinearLayout>    <LinearLayout        android:layout_width="match_parent"        android:layout_height="wrap_content"        android:orientation="horizontal" >        <TextView            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:text="密  码"            android:textSize="18sp" />        <EditText            android:id="@+id/psswd"            android:layout_width="match_parent"            android:layout_height="wrap_content"            android:password="true"            android:singleLine="true" >        </EditText>    </LinearLayout>    <CheckBox        android:id="@+id/check"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_marginTop="5dp"        android:checked="false"        android:text="记住密码" />    <LinearLayout        android:layout_width="match_parent"        android:layout_height="wrap_content"        android:gravity="center"        android:orientation="horizontal" >        <Button            android:id="@+id/login"            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:text="登陆" />        <Button            android:id="@+id/cancel"            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:text="取消" />    </LinearLayout></LinearLayout>

当记住密码未被勾选时，在以后登陆时的界面如下：

当记住密码被勾选时，在以后登陆时的界面如下：

用户的登录信息通过editor写入到xml文件中，如下：

user_info.xml文件里存储的是键值对。

下面给出官网的API对SharedPreferences的用法解释：

The SharedPreferences class provides a general framework that allows youto save and retrieve persistent key-value pairs of primitive data types. You can use SharedPreferences to save any primitive data: booleans, floats, ints, longs, andstrings. This data will persist across user sessions (even if your application is killed).

User Preferences

Shared preferences are not strictly for saving "user preferences," such as what ringtone auser has chosen. If you're interested in creating user preferences for your application, seePreferenceActivity, which provides an Activity framework for you to createuser preferences, which will be automatically persisted (using shared preferences).

To get a SharedPreferences object for your application, use one oftwo methods:

• getSharedPreferences() - Use this if you need multiple preferences files identified by name,which you specify with the first parameter.
• getPreferences() - Use this if you needonly one preferences file for your Activity. Because this will be the only preferences filefor your Activity, you don't supply a name.

To write values:

1. Call edit() to get aSharedPreferences.Editor.
2. Add values with methods such as putBoolean() andputString().
3. Commit the new values with commit()