- Dependency Injection Xamarin Visual Studio For Mac
- Visual Studio For Mac Os
- Xamarin For Visual Studio Download
- Xamarin Forms Dependency Injection
As of May 10th, 2017, Visual Studio for Mac replaced Xamarin Studio (Xamarin Studio 6.3 being the final release) and offers all the features of Xamarin Studio, plus cloud and web development, and contains improvements for cross-platform mobile development. Including MVVM, dependency injection, commands, EventAggregator, and others. This is also known as dependency injection. You will often run into limitations with PCLs with UI-related needs which require specialized handling on each platform. In my example I will be using the Xamarin.Mac and.NET Framework 4.5 Frameworks. It eliminates errors and code smells, its IntelliSense is better than Visual Studio IntelliSense, used for code editing helpers, instant code reviewer, and more. MFractor (Mac Only) A must-have mobile-first productivity tool for Visual Studio Mac that uses XAML to C# code generation, code issue fixing and image importing wizard. Dependency injection is a specialized version of the Inversion of Control (IoC) pattern, where the concern being inverted is the process of obtaining the required dependency. With dependency injection, another class is responsible for injecting dependencies into an object at runtime.
-->In some cases, you may get errors while installing Android support libraries. This guide provides workarounds for some common errors.
Overview
Instructions on how to install Visual Studio for Mac and additional components required for cross-platform development.docs.microsoft.com Xamarin approach to mobile development When it comes to mobile development, we got used to thinking that the only choice to build an app is to use native languages, Objective C and Swift — for iOS, Java. Visual Studio for Mac.NET. Azure DevOps. Failure installing Xamarin. Cannot download Oracle dependency. Reported by Curtis Hendrix Mar 05 at 02:34 PM windows 10.0.10240 visual studio 2017 version 15.5 Setup. During the installation of Xamarin, there is an Oracle download that fails.
While building a Xamarin.Android app project, you may get build errorswhen Visual Studio or Visual Studio for Mac attempt to download and installdependency libraries. Many of these errors are caused by networkconnectivity issues, file corruption, or versioning problems. Thisguide describes the most common support library installation errors andprovides the steps to work around these issues and get your app projectbuilding again.
Errors While Downloading m2Repository
You may see m2repository errors when referencing a NuGet package ofthe Android Support Libraries or Google Play services. The error messageresembles the following:
This example is for android_m2repository_r16, but you may see thissame error message for a different version such asandroid_m2repository_r18 or android_m2repository_r25.
Automatic Recovery from m2repository Errors
Often, this issue can be remedied by deleting the problematic libraryand rebuilding according to these steps:
Navigate to the support library directory on your computer:
On Windows, support libraries are located atC:UsersusernameAppDataLocalXamarin.
On Mac OS X, support libraries are located at /Users/username/.local/share/Xamarin.
Locate the library and version folder corresponding to the errormessage. For example, the library and version folder for the aboveerror message is located at Android.Support.v422.2.1:
Delete the contents of the version folder. Be sure to remove the.zip file as well as the content and embeddedsubdirectories within this folder. For the example error messageshown above, the files and subdirectories shown in this screenshot(content, embedded, and android_m2repository_r16.zip)are to be deleted:
Note that it is important to delete the entire contents of thisfolder. Although this folder may initially contain the 'missing'android_m2repository_r16.zip file, this file may have beenpartially downloaded or corrupted.
Rebuild the project – doing so will cause the build process tore-download the missing library.
In most cases, these steps will resolve the build error and allow youto continue. If deleting this library does not resolve the build error,you must manually download and install the android_m2repository_r_nn_.zipfile as described in the next section.
Manually Downloading m2repository
If you have tried using the automatic recovery steps above and stillhave build errors, you can manually download theandroid_m2repository_r_nn_.zip file (using a web browser) andinstall it according to the following steps. This procedure is alsouseful if you do not have internet access on your development computerbut you are able to download the archive using a different computer.
Download the android_m2repository_r_nn_.zip file that corresponds tothe error message – links are provided in the following list (along withthe corresponding MD5 hash of each link's URL):
android_m2repository_r33.zip– 5FB756A25962361D17BBE99C3B3FCC44
android_m2repository_r32.zip– F16A3455987DBAE5783F058F19F7FCDF
android_m2repository_r31.zip– 99A8907CE2324316E754A95E4C2D786E
android_m2repository_r30.zip– 05AD180B8BDC7C21D6BCB94DDE7F2C8F
android_m2repository_r29.zip– 2A3A8A6D6826EF6CC653030E7D695C41
android_m2repository_r28.zip– 17BE247580748F1EDB72E9F374AA0223
android_m2repository_r27.zip– C9FD4FCD69D7D12B1D9DF076B7BE4E1C
android_m2repository_r26.zip– 8157FC1C311BB36420C1D8992AF54A4D
android_m2repository_r25.zip– 0B3F1796C97C707339FB13AE8507AF50
android_m2repository_r24.zip– 8E3C9EC713781EDFE1EFBC5974136BEA
android_m2repository_r23.zip– D5BB66B3640FD9B9C6362C9DB5AB0FE7
android_m2repository_r22.zip– 96659D653BDE0FAEDB818170891F2BB0
android_m2repository_r21.zip– CD3223F2EFE068A26682B9E9C4B6FBB5
android_m2repository_r20.zip– 650E58DF02DB1A832386FA4A2DE46B1A
android_m2repository_r19.zip– 263B062D6EFAA8AEE39E9460B8A5851A
android_m2repository_r18.zip– 25947AD38DCB4865ABEB61522FAFDA0E
android_m2repository_r17.zip– 49054774F44AE5F35A6BA9D3C117EFD8
android_m2repository_r16.zip– 0595E577D19D31708195A83087881EE6
If the m2repository archive is not shown in this table, you can createthe download URL by prepending https://dl-ssl.google.com/android/repository/ tothe name of the m2repository to download. For example,use https://dl-ssl.google.com/android/repository/android_m2repository_r10.zto download android_m2repository_r10.zip.
Rename the file to the corresponding MD5 hash of the download URLas shown in the above table. For example, if you downloadedandroid_m2repository_r25.zip, rename it to0B3F1796C97C707339FB13AE8507AF50.zip. If the MD5 hash for thedownload URL of the downloaded file is not shown in the table, youcan use an online MD5 generator toconvert the URL to an MD5 hash string.
Copy the file to the Xamarin zips folder:
On Windows, this folder is located atC:UsersusernameAppDataLocalXamarinzips.
On Mac OS X, this folder is located at /Users/username/.local/share/Xamarin/zips.
For example, the following screenshot illustrates the result whenandroid_m2repository_r16.zip is downloaded and renamed to the MD5 hashof its download URL on Windows:
If this procedure does not resolve the build error, you mustmanually download the android_m2repository_r_nn_.zip file,unzip it, and install its contents as described in the next section.
Manually Downloading and Installing m2repository Files
The fully manual process for recovering from m2repository errors entailsdownloading the android_m2repository_r_nn_.zip file (using a web browser),unzipping it, and copying its contents to the support librarydirectory on your computer. In the following example, we'll recoverfrom this error message:
Use the following steps to download m2repository and installits contents:
Delete the contents of the library folder corresponding to theerror message. For example, in the above error message you woulddelete the contents ofC:UsersusernameAppDataLocalXamarinAndroid.Support.v423.1.1.0.As described earlier, you must delete the entire contents of thisdirectory:
Download the android_m2repository_r_nn_.zip file from Google thatcorresponds to the error message (see the table in the previous sectionfor links).
Extract this .zip archive to any location (such as theDesktop). This should create a directory that corresponds to thename of the .zip archive. Within this directory, you shouldfind a subdirectory called m2repository:
In the versioned library directory that you purged in step 1,re-create the content and embedded subdirectories. Forexample, the following screenshot illustrates content andembedded subdirectories being created in the 23.1.1.0 folderfor android_m2repository_r25.zip:
Copy m2repository from the extracted .zip into the content directorythat you created in the previous step:
In the extracted .zip directory, browse tom2repositorycomandroidsupportsupport-v4 and open the folder correspondingthe version number created above (in this example, 23.1.1):
Copy all of the files in this folder to the embedded directory created instep 4:
Verify that all files are copied over. The embedded directoryshould now contain files such as .jar, .aar, and .pom.
Unzip the contents of any extracted .aar files to the embeddeddirectory. On Windows, append a .zip extension to the .aarfile, open it, and copy the contents to the embedded directory.On macOS, unzip the .aar file by using the unzip command inthe Terminal (for example, unzip file.aar).
At this point, you have manually installed the missing componentsand your project should build without errors. If not, verify thatyou have downloaded the m2repository.zip archive version thatcorresponds exactly to the version in the error message, and verifythat you have installed its contents in the correct locations asdescribed in the above steps.
Dependency Injection Xamarin Visual Studio For Mac
Summary
This article explained how to recover from common errors that can takeplace during the automatic download and installation of dependencylibraries. It described how to delete the problematic library andrebuild the project as a way to re-download and re-install the library.It described how to download the library and install it in the zipsfolder. It also described a more involved procedure for manuallydownloading and installing the necessary files as a way to work aroundissues that cannot be resolved via automatic means.
This post was authored by guest blogger André Obelink, a Visual Basic MVP, and published by the VBTeam on his behalf.
In this first blog post of a series of two, I explain what dependency injection (DI) is and why you might want to use this design principle in your software. The target audience of this post is the junior / medium experienced software developer, with no knowledge of dependency injection or related techniques. In the second post, I’ll describe the use of Inversion of Control Containers (IoC containers), to use dependency injection in a much more flexible way.
Visual Studio For Mac Os
What is dependency injection?
Dependency injection isn’t new. It’s been around since the early 90s. Because it’s a design principle, it isn’t directly related to a specific programming language. For example, you can use this principle in Java, C#, or Visual Basic .NET. It’s one of the principles of SOLID. SOLID is a mnemonic acronym for the five basic principles of object-oriented programming and design. In my daily life as a software developer, I try to commit myself to apply the principles of SOLID. They were, years ago, defined by Robert C. Martin (also known as ‘Uncle Bob’). He’s the author of many books, including ‘Clean Code’. A highly recommended book!
Let’s start from the beginning by defining the term ‘dependency injection’. However, this is easier said than done. Wikipedia says: “In software engineering, dependency injection is a technique whereby one object supplies the dependencies of another object. A dependency is an object that can be used (a service). An injection is the passing of a dependency to a dependent object (a client) that would use it. The service is made part of the client’s state. Passing the service to the client, rather than allowing a client to build or find the service, is the fundamental requirement of the pattern.”
If you’re new to this subject, you may read this definition more than once and still have no clue what exactly is meant. I think an example from real life might help.
When you were a child, and you asked your mother to give you something to drink, you were happy when she handed you a cup of milk, a glass of orange juice, or a bottle of apple juice, for example. Your mother was in charge. You asked for a drink, but you didn’t know what you’d eventually get. The fact that you knew that you’d get some drink, without knowing exactly which drink it would be, describes more-or-less the core concept of dependency injection. You don’t know the exact type you’ll get, but you know about, for example, the methods on the interface.
Let’s look at another example from daily life, more related to computer software. Perhaps you’re familiar with Adobe Photoshop and their mechanism of plug-ins. You want to apply a filter to a photo. You can install a filter or plug-in, published by a third-party vendor. Adobe Photoshop doesn’t know anything about that filter. However, when this plug-in is installed, it can execute the filter logic, and apply that specific implementation of the filter to the active photo. Again, there’s a concept of not knowing about the filter that is installed, and the ability to apply that ‘unknown’ filter.
In my daily life as a developer, I use dependency injection a lot. Imagine, for example, the logging components we’re using in our software, like Log4net. Based on configuration, it logs to different – or a combination of – output destinations. In our code, we call something general like _logger.Log(“Hello!”). But when writing that code, we don’t know where this text will end up. Is it in a text file or is logged to the Windows Event log? Or both? Or will an email be sent containing the message?
Four roles
It’s important to understand that dependency injection involves four roles:
- The serviceobjects to be used.
- The clientobject that is depending on the services it uses.
- The interfaces that define how the client may use the services.
- The injector, which is responsible for constructing the services and injecting them into the client.
Xamarin For Visual Studio Download
The serviceobjects are the actual implementations of the logic you want to execute. In the example of the child asking for a drink, there are three ‘DrinkServices’: the MilkDrinkService, the OrangeJuiceDrinkService, and the AppleJuiceDrinkService.
The Child is the client object. It calls the Drink() method in one of the services. You can ask yourself the question: “How does the Child know that it can call something like a Drink() method?” As you perhaps know, the Child is not aware – and not allowed to be aware – of the MilkDrinkService or one of the other services.
The Child knows about the Drink() method, because it calls a method on an interface, in our example the IDrinkService. An interface defines the public members, but doesn’t implement them. See it as a contract or a description of the signature of the class. A service object, which implements an interface, contains the actual logic.
You can compare the mother of the child with the injector. She’s responsible for what kind of drink her child gets. The injector injects the actual logic.
Do some coding
I think that some code will clarify this abstract theory much better. It’s a best practice to start with defining the interface. In this case, the IDrinkService.
As you can see, it only defines which public methods are available. Because it always defines the public members, you must omit the keyword Public. And as I said earlier, it doesn’t contain any implementation.
The service objects implement the logic of the interface. The MilkDrinkService() implements IDrinkService. In practice, this means that we will write the specific implementation of the Drink() method in this class.
After you type ‘Implements IDrinkService’ and hits Enter, Visual Studio helps you by creating the method for you. Replace the ‘Throw New NotImplementedException()’ with the specific logic you want to execute in that service object. We have now implemented one of the service objects. The other two are quite similar. They differ only in the specific logic. Let’s add the second service object.
And the last service object isn’t hard to guess:
We now have coded all service objects. The next step is to define the client object. As you can remember, we must inject the service object into the consuming client object. There are a couple of ways to inject dependencies, but I’m choosing to use ‘constructor injection’. Other techniques are, for example, ‘setter injection’ or ‘interface injection’. The first example is self-explanatory: the client object exposes a setter method that the injector uses to inject the dependency. The second example is harder to understand. Interface injection concludes that the dependency provides an injector method that will inject the dependency into any client passed to it. Clients must implement an interface that exposes a setter method that accepts the dependency. For now, forget these other two injection techniques and let’s focus on constructor injection. In most cases, I use this type of injection because it always brings my client object in a valid state. To understand what I mean with this last statement, we should take a close look at the code.
Xamarin Forms Dependency Injection
As you can notice, I added a constructor that forces to apply an argument of the type IDrinkService. This means that we can only create an instance of this object, when we provide an object that implements this interface. So, an instance of my client object has always the mandatory _drinkService set. When other developers use one of my DrinkServices, they’re ‘unable’ to instantiate them in a wrong manner because Visual Studio is already telling them at design time that some mandatory information is missing (In comparison with setter injection, where this missing piece of code is only noticed when you’re already running the code).
Note that the client object has no references to – or knowledge of – our service objects. It’s only aware of the methods of the interfaces that it implements.
The fourth step is creating the injector. The injector is responsible for defining and injecting the dependency, in our example on of our DrinkServices.
You can imagine that the Mother class returns, based on some business logic or external configuration, one of the other services. The last part of our code example is using our classes.
When executing this code, this results in the following output:
You can play with this example by changing the implementation of the Mother.GetDrinkService() method. Our client object isn’t aware of the actual services. And if you decide tomorrow to create a BeerDrinkService() method that implements the IDrinkService interface, all depending code will still run fine.
Why using dependency injection?
The concept of dependency injection introduces some abstraction to your business logic. Some developers experience this as adding extra complexity to the code base. Other developers, including myself, think that it just removes complexity. For me, the main reason to apply these design principles is that it makes my code more loosely coupled. Loosely coupling helps you make your code better maintainable, extensible, and testable. It helps your applications to get more configurable: you can even change logic without recompiling.
By applying dependency injection, you will find that your classes contain in most cases only one responsibility and that’s a good thing. Single responsibility is one of the other five principles of SOLID. Indeed, you need dependency injection for a couple of other techniques defined by SOLID. I’m convinced that applying these techniques helps you write better software.
When writing unit tests, you will love these techniques even more! Imagine you have business logic that calculates the total amount of an order. The order, including the order lines, is retrieved from the database by an OrderRepository that implements the IOrderRepository.GetOrderByNumber() method. When you want to write a unit test that calculates the total order amount, this code relies on data in the database. But this is not what you want, because when data in your database is changed, your unit test will fail. Also, when running this unit test as part of the automated build in, for example, the cloud service VSTS, it can’t even connect with your database on premise.
So, to overcome this issue, when you want to unit test this piece code, the solution is to inject another service object that implements IOrderRepository too. For example, FakeOrderRepository. This fake or mock implementation will create an order and related lines in code. This code won’t normally change and can be executed independent from a database. Your unit tests will be much more predictable.
In this post, I have explained the concept of Dependency Injection. By introducing interfaces and implement them with a concrete and specific logic, your code will be more flexible, easier to understand, to extend and to maintain.
In the next post, I’ll show you the use of IoC containers, a technique that will help to assemble your application and other components by using dependency injection to a cohesive program.
Happy coding!
André Obelink
Twitter: @obelink
Blog: www.obelink.com
Links: