Quickstart: Azure Blob Storage client library v12 with Xamarin

Get started with the Azure Blob Storage client library v12 with Xamarin. Azure Blob Storage is Microsoft's object storage solution for the cloud. Follow steps to install the package and try out example code for basic tasks. Blob storage is optimized for storing massive amounts of unstructured data.

Use the Azure Blob Storage client library v12 with Xamarin to:

• Create a container
• Upload a blob to Azure Storage
• List all of the blobs in a container
• Download the blob to your device
• Delete a container

Reference links:

• API reference documentation
• Library source code
• Package (NuGet)
• Sample

Prerequisites

• Azure subscription - create one for trial
• Azure storage account - create a storage account
• Visual Studio with Mobile Development for .NET workload installed or Visual Studio for Mac

Setting up

This section walks you through preparing a project to work with the Azure Blob Storage client library v12 with Xamarin.

Create the project

1. Open Visual Studio and create a Blank Forms App.
2. Name it: BlobQuickstartV12

Install the package

1. Right-click your solution in the Solution Explorer pane and select Manage NuGet Packages for Solution.
2. Search for Azure.Storage.Blobs and install the latest stable version into all projects in your solution.

Set up the app framework

From the BlobQuickstartV12 directory:

1. Open up the MainPage.xaml file in your editor
2. Remove everything between the <ContentPage></ContentPage> elements and replace with the below:

<StackLayout HorizontalOptions="Center" VerticalOptions="Center">

    <Button x:Name="uploadButton" Text="Upload Blob" Clicked="Upload_Clicked"  IsEnabled="False"/>
    <Button x:Name="listButton" Text="List Blobs" Clicked="List_Clicked"  IsEnabled="False" />
    <Button x:Name="downloadButton" Text="Download Blob" Clicked="Download_Clicked"  IsEnabled="False" />
    <Button x:Name="deleteButton" Text="Delete Container" Clicked="Delete_Clicked" IsEnabled="False" />

    <Label Text="" x:Name="resultsLabel" HorizontalTextAlignment="Center" Margin="0,20,0,0" TextColor="Red" />

</StackLayout>

Copy your credentials from the Azure portal

When the sample application makes a request to Azure Storage, it must be authorized. To authorize a request, add your storage account credentials to the application as a connection string. View your storage account credentials by following these steps:

1. Sign in to the Azure portal.

2. Locate your storage account.

3. In the Settings section of the storage account overview, select Access keys. Here, you can view your account access keys and the complete connection string for each key.

4. Find the Connection string value under key1, and select the Copy button to copy the connection string. You will add the connection string value to an environment variable in the next step.

   

Configure your storage connection string

After you have copied your connection string, set it to a class level variable in your MainPage.xaml.cs file. Open up MainPaage.xaml.cs and find the storageConnectionString variable. Replace <yourconnectionstring> with your actual connection string.

Here's the code:

string storageConnectionString = "<yourconnectionstring>";

Object model

Azure Blob Storage is optimized for storing massive amounts of unstructured data. Unstructured data is data that does not adhere to a particular data model or definition, such as text or binary data. Blob storage offers three types of resources:

• The storage account
• A container in the storage account
• A blob in the container

The following diagram shows the relationship between these resources.

Use the following .NET classes to interact with these resources:

• BlobServiceClient: The BlobServiceClient class allows you to manipulate Azure Storage resources and blob containers.
• BlobContainerClient: The BlobContainerClient class allows you to manipulate Azure Storage containers and their blobs.
• BlobClient: The BlobClient class allows you to manipulate Azure Storage blobs.
• BlobDownloadInfo: The BlobDownloadInfo class represents the properties and content returned from downloading a blob.

Code examples

These example code snippets show you how to perform the following tasks with the Azure Blob Storage client library for .NET in a Xamarin.Forms app:

• Create class level variables
• Create a container
• Upload blobs to a container
• List the blobs in a container
• Download blobs
• Delete a container

Create class level variables

The code below declares several class level variables. They needed to communicate to Azure Blob Storage throughout the rest of this sample.

These are in addition to the connection string for the storage account set in the Configure your storage connection string section.

Add this code as class level variables inside the MainPage.xaml.cs file:

string storageConnectionString = "{set in the Configure your storage connection string section}";
string fileName = $"{Guid.NewGuid()}-temp.txt";

BlobServiceClient client;
BlobContainerClient containerClient;
BlobClient blobClient;

Create a container

Decide on a name for the new container. The code below appends a GUID value to the container name to ensure that it is unique.

Create an instance of the BlobServiceClient class. Then, call the CreateBlobContainerAsync method to create the container in your storage account.

Add this code to MainPage.xaml.cs file:

protected async override void OnAppearing()
{            
    string containerName = $"quickstartblobs{Guid.NewGuid()}";

    client = new BlobServiceClient(storageConnectionString);
    containerClient = await client.CreateBlobContainerAsync(containerName);

    resultsLabel.Text = "Container Created\n";

    blobClient = containerClient.GetBlobClient(fileName);

    uploadButton.IsEnabled = true;
}

Upload blobs to a container

The following code snippet:

1. Creates a MemoryStream of text.
2. Uploads the text to a Blob by calling the UploadAsync function of the BlobContainerClient class, passing it in both the filename and the MemoryStream of text. This method creates the blob if it doesn't already exist, and overwrites it if it does.

Add this code to the MainPage.xaml.cs file:

async void Upload_Clicked(object sender, EventArgs e)
{                                    
    using MemoryStream memoryStream = new MemoryStream(Encoding.UTF8.GetBytes("Hello World!"));

    await containerClient.UploadBlobAsync(fileName, memoryStream);

    resultsLabel.Text += "Blob Uploaded\n";

    uploadButton.IsEnabled = false;
    listButton.IsEnabled = true;
}

List the blobs in a container

List the blobs in the container by calling the GetBlobsAsync method. In this case, only one blob has been added to the container, so the listing operation returns just that one blob.

Add this code to the MainPage.xaml.cs file:

async void List_Clicked(object sender, EventArgs e)
{            
    await foreach (BlobItem blobItem in containerClient.GetBlobsAsync())
    {
        resultsLabel.Text += blobItem.Name + "\n";                
    }

    listButton.IsEnabled = false;
    downloadButton.IsEnabled = true;
}

Download blobs

Download the previously created blob by calling the ​Download​ToAsync method. The example code copies the Stream representation of the blob first into a MemoryStream and then into a StreamReader so the text can be displayed.

Add this code to the MainPage.xaml.cs file:

async void Download_Clicked(object sender, EventArgs e)
{
    BlobDownloadInfo downloadInfo = await blobClient.DownloadAsync();

    using MemoryStream memoryStream = new MemoryStream();

    await downloadInfo.Content.CopyToAsync(memoryStream);
    memoryStream.Position = 0;

    using StreamReader streamReader = new StreamReader(memoryStream);

    resultsLabel.Text += "Blob Contents: \n";
    resultsLabel.Text += await streamReader.ReadToEndAsync();
    resultsLabel.Text += "\n";

    downloadButton.IsEnabled = false;
    deleteButton.IsEnabled = true;
}

Delete a container

The following code cleans up the resources the app created by deleting the entire container by using ​DeleteAsync.

The app first prompts to confirm before it deletes the blob and container. This is a good chance to verify that the resources were created correctly, before they are deleted.

Add this code to the MainPage.xaml.cs file:

async void Delete_Clicked(object sender, EventArgs e)
{            
    var deleteContainer = await Application.Current.MainPage.DisplayAlert("Delete Container",
        "You are about to delete the container proceeed?", "OK", "Cancel");

    if (deleteContainer == false)
        return;

    await containerClient.DeleteAsync();

    resultsLabel.Text += "Container Deleted";

    deleteButton.IsEnabled = false;
}

Run the code

When the app starts, it will first create the container as it appears. Then you will need to click the buttons in order to upload, list, download the blobs, and delete the container.

To run the app on Windows press F5. To run the app on Mac press Cmd+Enter.

The app writes to the screen after every operation. The output of the app is similar to the example below:

Container Created
Blob Uploaded
98d9a472-8e98-4978-ba4f-081d69d2e6f8-temp.txt
Blob Contents:
Hello World!
Container Deleted

Before you begin the clean-up process, verify the output of the blob's contents on screen match the value that was uploaded.

After you've verified the values, confirm the prompt to delete the container and finish the demo.

Next steps

In this quickstart, you learned how to upload, download, and list blobs using Azure Blob Storage client library v12 with Xamarin.

To see Blob storage sample apps, continue to:

• To learn more about Xamarin, see Getting started with Xamarin.