Andriod四种存储——SharedPreferences

　　SharedPreferences是Android平台上一个轻量级的存储接口，用来保存应用的一些常用配置，比如Activity状态，Activity暂停时，将此Activity的状态保存到SharedPereferences中；当Activity重载，系统回调方法onSaveInstanceState时，再从SharedPreferences中将值取出.

　　　下面是一个保存登陆用户名的例子:

　　MyActivity:

package com.lee.SharedPreferenceStudy;

import android.app.Activity;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.view.View;
import android.widget.CheckBox;
import android.widget.EditText;
import android.widget.Toast;

public class MyActivity extends Activity {
    /**
     * Called when the activity is first created.
     */

    private EditText editText1,editText2;
    private CheckBox checkBox;
    private SharedPreferences preferences;
    private SharedPreferences.Editor editor;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        editText1  = (EditText) findViewById(R.id.userName_et);
        editText2 = (EditText) findViewById(R.id.password_et);
        checkBox = (CheckBox) findViewById(R.id.save_cb);
        //1.获得SharedPreferences的对象
        preferences =getSharedPreferences("UserInfo", MODE_PRIVATE);
        editor =preferences.edit();
        //2.取出数据
        String name =preferences.getString("username","");
        if (name==null){
            checkBox.setChecked(false);
            editor.remove("username");
            editor.commit();
        }else {
            checkBox.setChecked(true);
            editText1.setText(name);
        }

    }

    public  void  Sure(View view){
        switch (view.getId()){
            case R.id.ok_btn:
                String username =editText1.getText().toString().trim();
                String password =editText2.getText().toString().trim();
                if (username.equals("admin")&&password.equals("123")){
                    if (checkBox.isChecked()){
                        //3.存储数据
                        editor.putString("username",username);
                        //4.提交数据
                        editor.commit();
                    }else {
                        editor.remove("username");
                        editor.commit();
                    }
                    Toast.makeText(MyActivity.this,"登录成功",Toast.LENGTH_SHORT).show();
                }else {
                    Toast.makeText(MyActivity.this,"密码错误",Toast.LENGTH_SHORT).show();
                }
                break;
        }

    }
}

　　main.xml

 1 <?xml version="1.0" encoding="utf-8"?>
 2 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
 3               android:orientation="vertical"
 4               android:layout_width="fill_parent"
 5               android:layout_height="fill_parent"
 6         >
 7     <!--android:ems = "10" 设置TextView或者Edittext的宽度为10个字符的宽度。
 8     当设置该属性后，控件显示的长度就为10个字符的长度，超出的部分将不显示。-->
 9     <LinearLayout
10             android:orientation="horizontal"
11             android:layout_width="match_parent"
12             android:layout_height="wrap_content"
13             android:layout_gravity="center_horizontal">
14         <TextView
15                 android:layout_width="wrap_content"
16                 android:layout_height="wrap_content"
17                 android:text="用户名:"
18                 android:layout_margin="10dp"
19                 android:textSize="34sp"
20                 android:id="@+id/userName_tv"/>
21         <EditText
22                 android:layout_width="wrap_content"
23                 android:layout_height="match_parent"
24                 android:layout_margin="10dp"
25                 android:textSize="34sp"
26                 android:ems="10"
27                 android:textColor="#333333"
28                 android:id="@+id/userName_et"/>
29     </LinearLayout>
30     <LinearLayout
31             android:orientation="horizontal"
32             android:layout_width="match_parent"
33             android:layout_height="wrap_content">
34         <TextView
35                 android:layout_width="wrap_content"
36                 android:layout_height="wrap_content"
37                 android:text="密  码："
38                 android:layout_margin="10dp"
39                 android:textSize="34sp"
40                 android:id="@+id/password_tv"/>
41         <EditText
42                 android:layout_width="wrap_content"
43                 android:layout_height="match_parent"
44                 android:inputType="textPassword"
45                 android:ems="10"
46                 android:layout_margin="10dp"
47                 android:textSize="34sp"
48                 android:id="@+id/password_et"/>
49     </LinearLayout>
50     <LinearLayout
51             android:orientation="horizontal"
52             android:layout_width="match_parent"
53             android:layout_height="wrap_content">
54         <CheckBox android:layout_width="wrap_content"
55                   android:layout_height="wrap_content"
56                   android:layout_margin="10dp"
57                   android:checked="false"
58                   android:id="@+id/save_cb" android:enabled="true"/>
59         <TextView
60                 android:layout_width="wrap_content"
61                 android:layout_height="wrap_content"
62                 android:text="保存用户"
63                 android:layout_margin="10dp"
64                 android:textSize="34sp"
65                 android:id="@+id/save_tv"/>
66
67
68     </LinearLayout>
69     <LinearLayout android:layout_width="match_parent"
70                   android:layout_height="wrap_content"
71                   android:orientation="horizontal">
72         <Button android:layout_width="wrap_content"
73                 android:layout_height="wrap_content"
74                 android:text="确定"
75                 android:layout_weight="1"
76                 android:textSize="34sp"
77                 android:layout_margin="40dp"
78                 android:onClick="Sure"
79                 android:id="@+id/ok_btn"
80                 />
81         <Button android:layout_width="wrap_content"
82                 android:layout_height="wrap_content"
83                 android:text="取消"
84                 android:layout_weight="1"
85                 android:textSize="34sp"
86                 android:layout_margin="40dp"
87                 />
88     </LinearLayout>
89
90 </LinearLayout>

效果图：