Binding auto-reporting on remote changes
The client will invoke BindService to bind and start, if necessary the service. IServiceConnection object will be created to manage the connection between the client and the service.
If the client successfully binds to the service, then Android will return an object via the IServiceConnection that can be used to invoke methods on the service. The client then interacts with the service using this object. To review, here are the steps to bind to a service:. The need to cross process boundaries does introduce extra complexity: Recall that when a service is running the same process as the client, Android provides an IBinder object which may allow for two-way communication.
This is not the case with service running in its own process. A client communicates with a remote service with the the help of the Android. When a client requests to bind with the remote service, Android will invoke the Service. OnBind lifecycle method, which will return the internal IBinder object that is encapsulated by the Messenger.
The Messenger takes care of the communication between the two different processes. The developer is unconcerned with the details of serializing a message, marshalling the message across the process boundary, and then deserializing it on the client. This work is handled by the Messenger object. This diagram shows the client-side Android components that are involved when a client initiates binding to an out-of-process service:. The Service class in the remote process will go through the same lifecycle callbacks that a bound service in a local process will go through, and many of the APIs involved are the same.
OnCreate is used to initialize a Handler and inject that into Messenger object. Likewise, OnBind is overridden, but instead of returning an IBinder object, the service will return the Messenger. This diagram illustrates what happens in the service when a client is binding to it:.
When a Message is received by a service, it is processed by in instance of Android. The service will implement its own Handler subclass that must override the HandleMessage method. This method is invoked by the Messenger and receives the Message as a parameter. The Handler will inspect the Message meta-data and use that information to invoke methods on the service.
One-way communication occurs when a client creates a Message object and dispatches it to the service using the Messenger. Send will serialize the Message and hand that serialized data off to Android, which will route the message across the process boundary and to the service. The Messenger that is hosted by the service will create a Message object from the incoming data. This Message is placed into a queue, where messages are submitted one at a time to the Handler.
The Handler will inspect the meta-data contained in the Message and invoke the appropriate methods on the Service. The following diagram illustrates these various concepts in action:. This guide will discuss the details of implementing an out-of-process service. It will discuss how to implement a service that is meant to run in its own process and how a client may communicate with that service using the Messenger framework.
It will also briefly discuss two-way communication: Because services can be shared between different applications, this guide will also discuss one technique for limiting client access to the service by using Android permissions. Bugzilla - Services with isolated processes and custom Application class fail to resolve overloads properly reports that a Xamarin. Android service will not start up properly when the IsolatedProcess is set to true. This guide is provided for a reference.
Android application should still be able to communicate with an out-of-process service that is written in Java. Although it is possible to use implicit intents with apps that target older Android APIs, this guide will focus exclusively on the use of explicit intents. Apps targeting Android 5. As described above, the fact that a service is running in its own process means that some different APIs are involved.
As a quick overview, here are the steps to bind with and consume a remote service:. A service that is meant to run in its own process is, fundamentally, still a bound service. The service class will extend the base Service class and is decorated with the ServiceAttribute containing the meta-data that Android needs to bundle in the Android manifest. To begin with, the following properties of the ServiceAttribute that are important to an out-of-process service:. To run a service its own process, the Process property on the ServiceAttribute must be set to the name of the service.
To interact with outside applications, the Exported property should be set to true. If Exported is false , then only clients in the same APK i. What kind of process the service will run in depends on the value of the Process property.
Android identifies three different types of processes:. Private Process — A private process is one that is only available to the application that started it. To identify a process as private, its name must start with a: The service depicted in the previous code snippet and screenshot is a private process.
The following code snippet is an example of the ServiceAttribute:. Global Process — A service that is run in a global process is accessible to all applications running on the device. A global process must be a fully qualified class name that starts with a lower case character. Unless steps are taken to secure the service, other applications may bind and interact with it.
Securing the service against unauthorized use will be discussed later in this guide. Isolated Process — An isolated process is a process that runs in its own sandbox, isolated from the rest of the system and with no special permissions of its own. To run a service in an isolated process, the IsolatedProcess property of the ServiceAttribute is set to true as shown in this code snippet:.
See Bugzilla - Services with isolated processes and custom Application class fail to resolve overloads properly. An isolated service is a simple way to secure an application and the device against untrusted code. For example, an app may download and execute a script from a website.
In this case, performing this in an isolated process provides an additional layer of security against untrusted code compromising the Android device. Once a service has been exported, the name of the service should not change.
Changing the name of the service may break other applications that are using the service. To see the effect that the Process property has, the following screenshot shows a service running in its own private process:. Once the ServiceAttribute has been set, the service needs to implement a Handler. To process client requests, the service must implement a Handler and override the HandleMessage methodThis is the method takes a Message instance which which encapsulates the method call from the client and translates that call into some action or task that the service will perform.
The Message object exposes a property called What which is an integer value, the meaning of which is shared between the client and the service and relates to some task that the service is to perform for the client.
The following code snippet from the sample application shows one example of HandleMessage. In this example, there are two actions that a client can request of the service:.
By providing the Include clause, the data is retrieved using eager loading, which means all of the related data is retrieved through a single query of the database. In cases where most of the related data is not be used, eager loading can be less efficient because more data is retrieved. However, in this case, eager loading provides the best performance because the related data is displayed for each record.
By default, the data is sorted by the values of the property marked as the key. You can add an OrderBy clause to specify a different value for sorting. In this example, the default StudentID property is used for sorting. In the Sorting, Paging, and Filtering Data topic, you will enable the user to select a column for sorting. Run your web application, and navigate to the Students page. The Students page displays the following student information.
When working through this tutorial series, you can simply copy the code from the tutorial to your project. However, one disadvantage of this approach is that you may not become aware of the feature provided by Visual Studio to automatically generate code for model binding methods. When working on your own projects, automatic code generation can save you time and help you gain a sense of how to implement an operation.
This section describes the automatic code generation feature. This section is only informational and does not contain any code you need to implement in your project. Visual Studio not only creates a method in the code-behind with the proper signature, but also generates implementation code to assist you with performing the operation.
If you first set the ItemType property before using the automatic code generation feature, the generated code will use that type for the operations. For example, when setting the UpdateMethod property, the following code is automatically generated:. Again, the above code does not need to be added to your project.
In the next tutorial, you will implement methods for updating, deleting and adding new data. In this tutorial, you created data model classes and generated a database from those classes. You filled the database tables with test data. You used model binding to retrieve data from the database, and then displayed the data in a GridView.
In the next tutorial in this series, you will enable updating, deleting, and creating data. The feedback system for this content will be changing soon. Old comments will not be carried over. If content within a comment thread is important to you, please save a copy. For more information on the upcoming change, we invite you to read our blog post.
Software versions used in the tutorial Microsoft Visual Studio or Microsoft Visual Studio Express for Web This tutorial also works with Visual Studio but there will be some differences in the user interface and project template. What you'll build In this tutorial, you'll: Build data objects that reflect a university with students enrolled in courses Build database tables from the objects Populate the database with test data Display data in a web form Set up project In Visual Studio , create a new ASP.
Master as the master page for the new web form. Create the data models and database You will use Code First Migrations to create objects and the corresponding database tables. In the Models folder, add a new class named UniversityModels. You will use the tools for Code First Migrations to set up a database based on these classes.
SchoolContext If the command completes successfully you will receive a message stating migrations have been enabled, Notice that a new file named Configuration. To simplify the code for this demonstration project, only these properties were marked with data-validation attributes. In a real project, you would apply validation attributes to all properties that need validated data, such as properties in the Enrollment and Course classes. In Package Manager Console , run the command: If the command completes successfully you will receive a message stating migrations have been enabled,.
Notice that a new file named Configuration. In Visual Studio, this file is automatically opened after it is created. The Configuration class contains a Seed method which enables you to pre-populate the database tables with test data.
Add the following code to the Seed method. You'll need to add a using statement for the ContosoUniversityModelBinding. If you receive an exception when running this command, it is possible that the values for StudentID and CourseID have varied from the values in the Seed method. Add those values in the code for seeding the Enrollments table. The database file has been added, but it is currently hidden in the project.
Click Show All Files to display the file. The tables now exist and are populated with data. With data in the database, you are now ready to retrieve that data and display it in a web page. You will use a GridView control to display the data in columns and rows.
Within that placeholder, add a GridView control that includes the following code. There are a couple of important concepts in this markup code for you to notice. First, notice that a value is set for the SelectMethod property in the GridView element. This value specifies the name of the method that is used for retrieving data for the GridView. You will create this method in the next step. Second, notice that the ItemType property is set to the Student class that you created earlier. By setting this value, you can refer to properties of that class in the markup code.
For example, the Student class contains a collection named Enrollments. You can use Item. Enrollments to retrieve that collection and then use LINQ syntax to retrieve the sum of enrolled credits for each student.
In the code-behind file, you need to add the method that is specified for the SelectMethod value. Then, add the following method. Notice that the name of this method matches the name you provided for SelectMethod. The Include clause improves the performance of this query but is not essential for the query to work. Without the Include clause, the data would be retrieved using lazy loading, which involves sending a separate query to the database each time related data is retrieved.
By providing the Include clause, the data is retrieved using eager loading, which means all of the related data is retrieved through a single query of the database. In cases where most of the related data is not be used, eager loading can be less efficient because more data is retrieved. However, in this case, eager loading provides the best performance because the related data is displayed for each record. By default, the data is sorted by the values of the property marked as the key.