使用SharedPreferences保存key-value对的步骤如下:
(1)使用Context类提供的getSharedPreferences()方法,获取SharedPreferences对象。getSharedPreferences()方法的原型如下:
SharedPreferences sp=context.getSharedPreferences(String name, int mode);
其中,参数name表示存储数据的文件名。有一点需要注意的是,此处只是定义了该文件名,该文件实际上并没有被创建,该文件只有当创建了SharedPreferences.Edit对象并使用该对象的commit()方法提交数据时,才会被创建。参数mode用于指定文件的操作模式,其可选值有四种,如下:
Context.MODE_APPEND(内容追加模式)、
Context.MODE_PRIVATE(默认操作模式)、
Context.MODE_WORLD_READABLE(可读模式)、
Context.MODE_WORLD_WRITEABLE(可写模式)。
(2)使用SharedPreferences接口的edit获得SharedPreferences.Editor对象。使用Shared Preferences方式存储数据时需要借助SharedPreferences.Edit类提供的方法来添加数据。
(3)通过SharedPreferences.Editor接口的putXxx方法保存key-value对。其中Xxx表示不同的数据类型。例如:字符串类型的value需要用putString方法。
(4)通过SharedPreferences.Editor接口的commit方法保存key-value对。commit方法相当于数据库事务中的提交(commit)操作。
案例:
activity_main.xml:
<?xml version="1.0" encoding="utf-8"?><RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:id="@+id/activity_main" android:layout_width="match_parent" android:layout_height="match_parent" android:background="#A4D3EE" tools:context="com.example.login123.LoginActivity"> <include layout="@layout/login_top"></include> <ImageView android:id="@+id/imageView" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_alignParentBottom="true" android:src="@drawable/deer" /></RelativeLayout>
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activity_two.xml:
<?xml version="1.0" encoding="utf-8"?><RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:id="@+id/activity_two" android:layout_width="match_parent" android:layout_height="match_parent" android:paddingBottom="@dimen/activity_vertical_margin" android:paddingLeft="@dimen/activity_horizontal_margin" android:paddingRight="@dimen/activity_horizontal_margin" android:paddingTop="@dimen/activity_vertical_margin" tools:context="com.example.login123.TwoActivity"> <TextView android:id="@+id/textView" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_centerHorizontal="true" android:layout_centerVertical="true" android:text="Welcome" android:textSize="40sp" /></RelativeLayout>
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login_top.xml:
<?xml version="1.0" encoding="utf-8"?><RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical" android:padding="32dp"> <LinearLayout android:layout_width="match_parent" android:layout_height="wrap_content" android:background="@drawable/logintop_roundbg" android:orientation="vertical" android:padding="@dimen/activity_horizontal_margin"> <EditText android:id="@+id/etName" android:layout_width="match_parent" android:layout_height="wrap_content" android:background="#ffffff" android:drawableLeft="@drawable/icon_user" android:drawablePadding="10dp" android:ems="10" android:hint="请输入账号"> <requestFocus /> </EditText> <EditText android:id="@+id/etPassword" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_below="@id/etName" android:layout_marginTop="10dp" android:background="#ffffff" android:drawableLeft="@drawable/icon_pass" android:drawablePadding="10dp" android:ems="10" android:hint="请输入密码" /> <LinearLayout android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_below="@+id/etPassword"> <CheckBox android:id="@+id/cbIsRememberPass" android:layout_width="0dp" android:layout_height="wrap_content" android:layout_marginTop="10dp" android:layout_weight="1" android:text="记住密码" android:textSize="20sp" /> <Button android:layout_width="0dp" android:layout_height="wrap_content" android:layout_marginTop="10dp" android:layout_weight="1" android:background="#6495ED" android:onClick="login" android:text="登录" /> </LinearLayout> </LinearLayout></RelativeLayout>
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该布局主要放置登录所输入的用户名和密码、
LoginActivity.Java:
package com.example.login123;import android.content.Context;import android.content.Intent;import android.content.SharedPreferences;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.view.View;import android.widget.CheckBox;import android.widget.EditText;import android.widget.Toast;public class LoginActivity extends AppCompatActivity { private EditText etName; private EditText etPassword; private CheckBox cbIsRememberPass; private SharedPreferences sharedPreferences; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); initViews(); sharedPreferences = getSharedPreferences("rememberpassword", Context.MODE_PRIVATE); boolean isRemember = sharedPreferences.getBoolean("rememberpassword", false); if (isRemember) { String name = sharedPreferences.getString("name", ""); String password = sharedPreferences.getString("password", ""); etName.setText(name); etPassword.setText(password); cbIsRememberPass.setChecked(true); } } public void initViews() { etName = (EditText) findViewById(R.id.etName); etPassword = (EditText) findViewById(R.id.etPassword); cbIsRememberPass = (CheckBox) findViewById(R.id.cbIsRememberPass); } public void login(View view) { String name = etName.getText().toString(); String password = etPassword.getText().toString(); if ("admin".equals(name) && "123456".equals(password)) { SharedPreferences.Editor editor = sharedPreferences.edit(); if (cbIsRememberPass.isChecked()) { editor.putBoolean("rememberpassword", true); editor.putString("name", name); editor.putString("password", password); } else { editor.clear(); } editor.commit(); Intent intent = new Intent(this, TwoActivity.class); startActivity(intent); finish(); } else { Toast.makeText(this, "账号或密码错误", Toast.LENGTH_LONG); } }}
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TwoActivity.java:
package com.example.login123;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;public class TwoActivity extends AppCompatActivity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_two); }}
运行结果:
注意:
SharedPreferences使用很简单,但一定要注意以下几点:
(1)存入数据和删除数据时,一定要在最后使用editor.commit()方法提交数据。
(2)获取数据的key值与存入数据的key值得数据类型要一致,否则查不到数据。
(3)保存SharedPreferences的key值时,可以用静态变量保存,以免储存、删除时写错了。
如:private static final String key=”itcast”;
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