Android uses application objects to access public data

When running each application, the Android system creates a application object that stores the public variables associated with the entire application. An Android application generates only one application object, and the Application object is the same in the unused activity, so the Application object is a single instance (SingleTon). Application objects are ideal for storing data related to the entire application, such as application versions, application login accounts, data caching, and so on.

Using application objects to store public data or data delivery
In Android development, activity switching is frequent, almost as much as switching from one Web page to another. There is a need to store public information (such as only one current logged-on user) and data transfer between different activity. The following is a way to store logged on user information using the Application object, which can be found to be very convenient for different activity to obtain login user information.

First, create a new Java class to inherit the application class: Myapplication.java

code is as follows

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Package com.example.applicationtest; Import android.app.Application; Public class MyApplication extends application {    public String appversion = "v1.0";    //the current logged-on user  private User Loginuser = new user ();      public user Getloginuser () {   return Loginuser;  }    public void userlogin (user user) {   loginuser.setuserid (User.getuserid ());   loginuser.setusername (User.getusername ());  }    public void Userlogout () {   loginuser = new User ();  } }

Specify the application's Application object in Androidmanifest.xml

The code is as follows

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<?xml version= "1.0" encoding= "Utf-8"?> <manifest xmlns:android= "Http://schemas.android.com/apk/res/android" Package= "Com.example.applicationtest" Android:versioncode= "1" Android:versionname= "1.0" > <uses-sdk Android:minsdkversion= "8" Android:targetsdkversion= "/>" <application Android:name= "Com.example.applicationtest.MyApplication" Android:allowbackup= "true" android:icon= "@drawable/ic_launcher" Android:label= "@string/app_name" Android:theme= "@style/apptheme" > <activity Android:name= "Com.example.applicationtest.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> </application> </manifest>

Use the Application object in the activity, using the Getapplication () method of the activity.

The code is as follows

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Package com.example.applicationtest; Import Android.os.Bundle; Import android.app.Activity; public class Mainactivity extends activity { Private MyApplication mapplication; @Override protected void OnCreate (Bundle savedinstancestate) { Super.oncreate (savedinstancestate); Setcontentview (R.layout.activity_main); Get the Application object for the entire application The objects obtained in different activity are the same Mapplication = (MyApplication) getapplication (); } /** * Generally only in the login interface to set the login user information, in other activity * Access to login user information as long as the application object is passed */ private void Login () { User user = new user (); User.setuserid (1); User.setusername ("Raysmond"); To save the logon user information to the Application object Mapplication.userlogin (user); } }

It can be found that data sharing can be easily realized between different activity through application objects. This is much more convenient than passing data through bundle each time the activity is switched.

The traditional way of using bundle to pass data before an activity
Suppose we have two activity:activity1 and activity2,activity1 switching to Activity2 and passing user information.

The code is as follows

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Activity1.java Package com.example.applicationtest; Import Android.os.Bundle; Import android.app.Activity; Import android.content.Intent; public class Activity1 extends activity { @Override protected void OnCreate (Bundle savedinstancestate) { Super.oncreate (savedinstancestate); Setcontentview (r.layout.activity_activity1); Switch to Activity2 GotoActivity2 (); } private void GotoActivity2 () { Intent Intent = new Intent (activity1.this,activity2.class); Bundle Bundle = new Bundle (); Bundle.putlong ("user_id", 1); Bundle.putstring ("user_name", "Raysmond"); Intent.putextras (bundle); StartActivity (Intent); } } Activity2.java Package com.example.applicationtest; Import Android.os.Bundle; Import android.app.Activity; Import android.content.Intent; public class Activity2 extends activity { @Override protected void OnCreate (Bundle savedinstancestate) { Super.oncreate (savedinstancestate); Setcontentview (R.layout.activity_activity2); GetUserInfo (); } /** * Get the data passed from the last activity. */ private void GetUserInfo () { Intent Intent = This.getintent (); Bundle Bundle = Intent.getextras (); Long userId = Bundle.getlong ("user_id", -1l); String userName = bundle.getstring ("user_name"); } }

We can see that this is a cumbersome way to pass data, especially when there are many active and frequent shifts. The use of application objects is more concise and convenient when the entire application of public data (such as login information) is the same and needs to be used between different activity.