android实例教程

In this tutorial we’ll use Shared Preferences in our android application to store data in the form of key-value pair.
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在本教程中，我们将在Android应用程序中使用“ 共享首选项 ”以键值对的形式存储数据。
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Android共享首选项概述 (Android Shared Preferences Overview)

Shared Preferences allows activities and applications to keep preferences, in the form of key-value pairs similar to a Map that will persist even when the user closes the application.

共享首选项允许活动和应用程序以键-值对的形式保留首选项，类似于键映射对，即使用户关闭应用程序，该映射也将保留。

Android stores Shared Preferences settings as XML file in shared_prefs folder under DATA/data/{application package} directory. The DATA folder can be obtained by calling Environment.getDataDirectory().

Android将“共享首选项”设置作为XML文件存储在DATA / data / {application package}目录下的shared_prefs文件夹中。 可以通过调用Environment.getDataDirectory()获得DATA文件夹。

SharedPreferences is application specific, i.e. the data is lost on performing one of the following options:

SharedPreferences是特定于应用程序的，即在执行以下选项之一时数据会丢失：

• on uninstalling the application关于卸载应用程序
• on clearing the application data (through Settings)清除应用程序数据时（通过“设置”）

As the name suggests, the primary purpose is to store user-specified configuration details, such as user specific settings, keeping the user logged into the application.

顾名思义，其主要目的是存储用户指定的配置详细信息，例如用户特定的设置，以保持用户登录到应用程序中。

To get access to the preferences, we have three APIs to choose from:

要访问首选项，我们提供了三种API供您选择：

• getPreferences() : used from within your Activity, to access activity-specific preferencesgetPreferences（） ：从您的“活动”内部使用，以访问特定于活动的首选项
• getSharedPreferences() : used from within your Activity (or other application Context), to access application-level preferencesgetSharedPreferences（） ：从您的Activity（或其他应用程序上下文）内部使用，用于访问应用程序级首选项
• getDefaultSharedPreferences() : used on the PreferenceManager, to get the shared preferences that work in concert with Android’s overall preference frameworkgetDefaultSharedPreferences（） ：在PreferenceManager上使用，以获取与Android总体首选项框架协同工作的共享首选项

In this tutorial we’ll go with getSharedPreferences(). The method is defined as follows:

在本教程中，我们将使用getSharedPreferences() 。 该方法定义如下：

getSharedPreferences (String PREFS_NAME, int mode)

getSharedPreferences (String PREFS_NAME, int mode)

PREFS_NAME is the name of the file.

PREFS_NAME是文件名。

mode is the operating mode.

模式是操作模式。

Following are the operating modes applicable:

以下是适用的操作模式：

• MODE_PRIVATE: the default mode, where the created file can only be accessed by the calling applicationMODE_PRIVATE ：默认模式，其中创建的文件只能由调用应用程序访问
• MODE_WORLD_READABLE: Creating world-readable files is very dangerous, and likely to cause security holes in applicationsMODE_WORLD_READABLE ：创建世界可读的文件非常危险，并且可能在应用程序中造成安全漏洞
• MODE_WORLD_WRITEABLE: Creating world-writable files is very dangerous, and likely to cause security holes in applicationsMODE_WORLD_WRITEABLE ：创建可写入世界的文件非常危险，并且可能在应用程序中引起安全漏洞
• MODE_MULTI_PROCESS: This method will check for modification of preferences even if the Shared Preference instance has already been loadedMODE_MULTI_PROCESS ：即使已加载共享首选项实例，此方法也将检查首选项的修改
• MODE_APPEND: This will append the new preferences with the already existing preferencesMODE_APPEND ：这会将新的首选项附加到已经存在的首选项中
• MODE_ENABLE_WRITE_AHEAD_LOGGING: Database open flag. When it is set, it would enable write ahead logging by defaultMODE_ENABLE_WRITE_AHEAD_LOGGING ：数据库打开标志。 设置后，默认情况下将启用预写日志记录

初始化 (Initialization)

We need an editor to edit and save the changes in shared preferences. The following code can be used to get the shared preferences.

我们需要一个编辑器来编辑并保存共享首选项中的更改。 以下代码可用于获取共享的首选项。

SharedPreferences pref = getApplicationContext().getSharedPreferences("MyPref", 0); // 0 - for private mode
Editor editor = pref.edit();

储存资料 (Storing Data)

editor.commit() is used in order to save changes to shared preferences.

使用editor.commit（）来将更改保存到共享首选项。

editor.putBoolean("key_name", true); // Storing boolean - true/false
editor.putString("key_name", "string value"); // Storing string
editor.putInt("key_name", "int value"); // Storing integer
editor.putFloat("key_name", "float value"); // Storing float
editor.putLong("key_name", "long value"); // Storing longeditor.commit(); // commit changes

检索数据 (Retrieving Data)

Data can be retrieved from saved preferences by calling getString() as follows:

可以通过调用getString（）从保存的首选项中检索数据，如下所示：

pref.getString("key_name", null); // getting String
pref.getInt("key_name", -1); // getting Integer
pref.getFloat("key_name", null); // getting Float
pref.getLong("key_name", null); // getting Long
pref.getBoolean("key_name", null); // getting boolean

清除或删除数据 (Clearing or Deleting Data)

remove(“key_name”) is used to delete that particular value.

remove（“ key_name”）用于删除该特定值。

clear() is used to remove all data

clear（）用于删除所有数据

editor.remove("name"); // will delete key name
editor.remove("email"); // will delete key emaileditor.commit(); // commit changes

editor.clear();
editor.commit(); // commit changes

项目结构 (Project Structure)

Android共享首选项项目代码 (Android Shared Preferences Project Code)

The activity_main.xml layout consists of two EditText views which store and display name and email. The three buttons implement their respective onClicks in the MainActivity.

activity_main.xml布局由两个EditText视图组成，这些视图存储并显示名称和电子邮件。 这三个按钮在MainActivity实现各自的onClicks。

<RelativeLayout xmlns:android="https://schemas.android.com/apk/res/android"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" ><Buttonandroid:id="@+id/btnSave"android:layout_width="wrap_content"android:layout_height="wrap_content"android:layout_centerVertical="true"android:layout_alignParentLeft="true"android:layout_alignParentStart="true"android:onClick="Save"android:text="Save" /><Buttonandroid:id="@+id/btnRetr"android:layout_width="wrap_content"android:layout_height="wrap_content"android:layout_centerHorizontal="true"android:layout_centerVertical="true"android:onClick="Get"android:text="Retrieve" /><Buttonandroid:id="@+id/btnClear"android:layout_width="wrap_content"android:layout_height="wrap_content"android:layout_alignRight="@+id/etEmail"android:layout_centerVertical="true"android:layout_alignParentRight="true"android:layout_alignParentEnd="true"android:onClick="clear"android:text="Clear" /><EditTextandroid:id="@+id/etEmail"android:layout_width="match_parent"android:layout_height="wrap_content"android:ems="10"android:hint="Email"android:inputType="textEmailAddress"android:layout_below="@+id/etName"android:layout_marginTop="20dp"android:layout_alignParentRight="true"android:layout_alignParentEnd="true" /><EditTextandroid:id="@+id/etName"android:layout_width="match_parent"android:layout_height="wrap_content"android:ems="10"android:hint="Name"android:inputType="text"android:layout_alignParentTop="true"android:layout_alignLeft="@+id/etEmail"android:layout_alignStart="@+id/etEmail" /></RelativeLayout>

The MainActivity.java file is used to save and retrieve the data through keys.

MainActivity.java文件用于通过键保存和检索数据。

package com.journaldev.sharedpreferences;import android.app.Activity;
import android.content.Context;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.widget.TextView;public class MainActivity extends Activity {SharedPreferences sharedpreferences;TextView name;TextView email;public static final String mypreference = "mypref";public static final String Name = "nameKey";public static final String Email = "emailKey";@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);name = (TextView) findViewById(R.id.etName);email = (TextView) findViewById(R.id.etEmail);sharedpreferences = getSharedPreferences(mypreference,Context.MODE_PRIVATE);if (sharedpreferences.contains(Name)) {name.setText(sharedpreferences.getString(Name, ""));}if (sharedpreferences.contains(Email)) {email.setText(sharedpreferences.getString(Email, ""));}}public void Save(View view) {String n = name.getText().toString();String e = email.getText().toString();SharedPreferences.Editor editor = sharedpreferences.edit();editor.putString(Name, n);editor.putString(Email, e);editor.commit();}public void clear(View view) {name = (TextView) findViewById(R.id.etName);email = (TextView) findViewById(R.id.etEmail);name.setText("");email.setText("");}public void Get(View view) {name = (TextView) findViewById(R.id.etName);email = (TextView) findViewById(R.id.etEmail);sharedpreferences = getSharedPreferences(mypreference,Context.MODE_PRIVATE);if (sharedpreferences.contains(Name)) {name.setText(sharedpreferences.getString(Name, ""));}if (sharedpreferences.contains(Email)) {email.setText(sharedpreferences.getString(Email, ""));}}@Overridepublic boolean onCreateOptionsMenu(Menu menu) {// Inflate the menu; this adds items to the action bar if it is present.getMenuInflater().inflate(R.menu.menu_main, menu);return true;}}

mypreference is the name of the file where the shared preferences key-value pair is stored.

mypreference是存储共享首选项键值对的文件的名称。

The image below shows the final output of our project:

下图显示了我们项目的最终输出：

This brings an end to this tutorial. You can download the project Android Shared Preferences from the below link.

本教程到此结束。 您可以从下面的链接下载项目Android共享首选项 。

翻译自: https://www.journaldev.com/9412/android-shared-preferences-example-tutorial

android实例教程