Android 简明教程

Android - Session Management

会话在您想将用户数据存储应用程序外时为您提供帮助，这样在下一次用户使用您的应用程序时，您可以轻松地找回他的详细信息并相应地执行操作。

Session help you when want to store user data outside your application, so that when the next time user use your application, you can easily get back his details and perform accordingly.

这可以通过很多方式完成。但最简单、最棒的方式是通过 Shared Preferences 。

This can be done in many ways. But the most easiest and nicest way of doing this is through Shared Preferences.

Shared Preferences

共享首选项允许您保存和检索键值对形式的数据。为了使用共享首选项，您必须调用 getSharedPreferences() 方法，该方法返回一个指向包含首选项值的文件的 SharedPreference 实例。

Shared Preferences allow you to save and retrieve data in the form of key,value pair. In order to use shared preferences, you have to call a method getSharedPreferences() that returns a SharedPreference instance pointing to the file that contains the values of preferences.

SharedPreferences sharedpreferences = getSharedPreferences(MyPREFERENCES, Context.MODE_PRIVATE);

您可以使用 SharedPreferences.Editor 类在 sharedpreferences 中保存一些东西。您将调用 SharedPreference 实例的 edit 方法，并在 editor 对象中接收它。它的语法是 −

You can save something in the sharedpreferences by using SharedPreferences.Editor class. You will call the edit method of SharedPreference instance and will receive it in an editor object. Its syntax is −

Editor editor = sharedpreferences.edit();
editor.putString("key", "value");
editor.commit();

除了 putString 方法外，editor 类中还有允许在共享首选项中操作数据的方法。它们列出如下 −

Apart from the putString method, there are methods available in the editor class that allows manipulation of data inside shared preferences. They are listed as follows −

Sr.No

Mode & description

1

apply() It is an abstract method. It will commit your changes back from editor to the sharedPreference object you are calling

2

clear() It will remove all values from the editor

3

remove(String key) It will remove the value whose key has been passed as a parameter

4

putLong(String key, long value) It will save a long value in a preference editor

5

putInt(String key, int value) It will save a integer value in a preference editor

6

putFloat(String key, float value) It will save a float value in a preference editor

Session Management through Shared Preferences

为了从共享首选项执行会话管理，我们需要在 onResume 方法中检查共享首选项中存储的值或数据。如果没有数据，我们将从应用程序的开始部分启动应用程序，如同新安装时一样。但如果我们获取了数据，我们将会从用户离开它的位置开始。在下面的示例中会有演示 −

In order to perform session management from shared preferences, we need to check the values or data stored in shared preferences in the onResume method. If we don’t have the data, we will start the application from the beginning as it is newly installed. But if we got the data, we will start from the where the user left it. It is demonstrated in the example below −

Example

以下示例演示了会话管理的用法。它创建了一个基本应用程序，允许你首次登录。然后，当你退出应用程序而不退出时，如果你重新启动应用程序，你将被带回相同的地方。但如果你从应用程序退出，你将被带回到主登录屏幕。

The below example demonstrates the use of Session Management. It crates a basic application that allows you to login for the first time. And then when you exit the application without logging out, you will be brought back to the same place if you start the application again. But if you logout from the application, you will be brought back to the main login screen.

要尝试本示例，您需要在实际设备或模拟器上运行它。

To experiment with this example, you need to run this on an actual device or in an emulator.

Steps

Description

1

You will use android studio IDE to create an Android application under a package com.example.sairamkrishna.myapplication.

2

Modify src/MainActivity.java file to add progress code to add session code.

3

Create New Activity and it name as second.java.Edit this file to add progress code to add session code.

4

Modify res/layout/activity_main.xml file to add respective XML code.

5

Modify res/layout/second_main.xml file to add respective XML code.

7

Run the application and choose a running android device and install the application on it and verify the results.

以下是 MainActivity.java 的内容。

Here is the content of MainActivity.java.

package com.example.sairamkrishna.myapplication;

import android.content.Context;
import android.content.Intent;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

public class MainActivity extends AppCompatActivity {
   EditText ed1,ed2,ed3;
   Button b1;
   Intent in;

   public static final String MyPREFERENCES = "MyPrefs" ;
   public static final String Name = "nameKey";
   public static final String Phone = "phoneKey";
   public static final String Email = "emailKey";
   SharedPreferences sharedpreferences;

   @Override
   protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);

      ed1=(EditText)findViewById(R.id.editText);
      ed2=(EditText)findViewById(R.id.editText2);
      ed3=(EditText)findViewById(R.id.editText3);

      b1=(Button)findViewById(R.id.button);
      sharedpreferences = getSharedPreferences(MyPREFERENCES, Context.MODE_PRIVATE);

      b1.setOnClickListener(new View.OnClickListener() {
         @Override
         public void onClick(View v) {
            String n  = ed1.getText().toString();
            String ph  = ed2.getText().toString();
            String e  = ed3.getText().toString();

            SharedPreferences.Editor editor = sharedpreferences.edit();

            editor.putString(Name, n);
            editor.putString(Phone, ph);
            editor.putString(Email, e);
            editor.commit();

            in = new Intent(MainActivity.this,second_main.class);
            startActivity(in);
         }
      });
   }
}

以下是 second_main.java 的内容。

Here is the content of second_main.java.

package com.example.sairamkrishna.myapplication;

import android.app.Activity;
import android.content.Context;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

public class second_main extends Activity {
   Button bu=null;
   Button bu2=null;

   @Override
   protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.second_main);

      bu=(Button)findViewById(R.id.button2);
      bu2=(Button)findViewById(R.id.button3);
   }

   public  void logout(View view){
      SharedPreferences sharedpreferences = getSharedPreferences(MainActivity.MyPREFERENCES, Context.MODE_PRIVATE);
      SharedPreferences.Editor editor = sharedpreferences.edit();
      editor.clear();
      editor.commit();
   }

   public void close(View view){
      finish();
   }
}

以下是 activity_main.xml 的内容。

Here is the content of 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:layout_width="match_parent"
   android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
   android:paddingRight="@dimen/activity_horizontal_margin"
   android:paddingTop="@dimen/activity_vertical_margin"
   android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity">

   <TextView
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="Shared Preference"
      android:id="@+id/textView"
      android:layout_alignParentTop="true"
      android:layout_centerHorizontal="true"
      android:textSize="35dp" />

   <TextView
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="Tutorials Point"
      android:id="@+id/textView2"
      android:layout_below="@+id/textView"
      android:layout_centerHorizontal="true"
      android:textSize="35dp"
      android:textColor="#ff16ff01" />

   <EditText
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:id="@+id/editText"
      android:layout_below="@+id/textView2"
      android:layout_marginTop="67dp"
      android:hint="Name"
      android:layout_alignParentRight="true"
      android:layout_alignParentEnd="true"
      android:layout_alignParentLeft="true"
      android:layout_alignParentStart="true" />

   <EditText
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:id="@+id/editText2"
      android:layout_below="@+id/editText"
      android:layout_alignParentLeft="true"
      android:layout_alignParentStart="true"
      android:layout_alignParentRight="true"
      android:layout_alignParentEnd="true"
      android:hint="Pass" />

   <EditText
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:id="@+id/editText3"
      android:layout_below="@+id/editText2"
      android:layout_alignParentLeft="true"
      android:layout_alignParentStart="true"
      android:layout_alignParentRight="true"
      android:layout_alignParentEnd="true"
      android:hint="Email" />

   <Button
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="login"
      android:id="@+id/button"
      android:layout_below="@+id/editText3"
      android:layout_centerHorizontal="true"
      android:layout_marginTop="50dp" />

</RelativeLayout>

以下是 second_main.xml 的内容。

Here is the content of second_main.xml.

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
   android:orientation="vertical" android:layout_width="match_parent"
   android:layout_height="match_parent">

   <Button
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="Logout"
      android:onClick="logout"
      android:id="@+id/button2"
      android:layout_gravity="center_horizontal"
      android:layout_alignParentTop="true"
      android:layout_centerHorizontal="true"
      android:layout_marginTop="191dp" />

   <Button
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="Close"
      android:onClick="close"
      android:id="@+id/button3"
      android:layout_below="@+id/button2"
      android:layout_centerHorizontal="true"
      android:layout_marginTop="69dp" />

</RelativeLayout>

以下是 Strings.xml 的内容。

Here is the content of Strings.xml.

<resources>
   <string name="app_name">My Application</string>
</resources>

以下是 AndroidManifest.xml 的内容。

Here is the content of AndroidManifest.xml.

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
   package="com.example.sairamkrishna.myapplication" >

   <application
      android:allowBackup="true"
      android:icon="@mipmap/ic_launcher"
      android:label="@string/app_name"
      android:theme="@style/AppTheme" >

      <activity
         android:name=".MainActivity"
         android:label="@string/app_name" >

         <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
         </intent-filter>

      </activity>

      <activity android:name=".second"></activity>

   </application>
</manifest>

让我们尝试运行你的应用程序。我假设你在执行环境设置时已创建了你的 AVD。要从 Android Studio 运行应用程序，请打开项目的一个活动文件，然后从工具栏中单击运行图标。Android Studio 将应用程序安装到你的 AVD 上并启动它，如果你的设置和应用程序一切正常，它将显示以下模拟器窗口 −

Let’s try to run your application. I assume you had created your AVD while doing environment setup. To run the app from Android studio, open one of your project’s activity files and click Run icon from the tool bar. Android studio installs the app on your AVD and starts it and if everything is fine with your set-up and application, it will display following Emulator window −

session

输入你的用户名和密码 (type anything you like, but remember what you type) ，然后单击登录按钮。如下图所示 −

Type in your username and password (type anything you like, but remember what you type), and click on login button. It is shown in the image below −

session1

只要单击登录按钮，你就会被带到此欢迎屏幕。现在你的登录信息存储在共享首选项中。

As soon as you click on login button, you will be brought to this Welcome screen. Now your login information is stored in shared preferences.

session2

现在单击 Exit without logout 按钮，你将被带回到主屏幕，首选项文件中的输出将如以下图像所示

Now click on Exit without logout button and you will be brought back to the home screen and in preference file out put would be as shown below image

shared

如果您以注释文件的形式打开 myPref.xml 文件，它将如下所示

If you open myPref.xml file as note file, it would be as follows

session note

如果您单击注销按钮，它将清除首选项值。并且如果您输入不同值作为输入，它将在 XML 中将这些值输入为首选项。

If you click on logout button, it will erase preference values. and if you entered different values as inputs,it will enter those values as preference in XML.