Develop Android App On Mac

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  1. Develop Android App With Python
  2. Building Android App With Machine Learning
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In this two-part guide, you will build your first Xamarin.Android application with Visual Studio and develop an understanding of the fundamentals of Android application development with Xamarin.

You will create an application that translates analphanumeric phone number (entered by the user) into a numeric phonenumber and display the numeric phone number to the user. The final application looks likethis:

Windows requirements

To follow along with this walkthrough, you will need the following:

  • Windows 10.

  • Visual Studio 2019 or Visual Studio 2017 (version 15.8 or later): Community, Professional, or Enterprise.

macOS requirements

To follow along with this walkthrough, you will need the following:

  • The latest version of Visual Studio for Mac.

  • A Mac running macOS High Sierra (10.13) or later.

This walkthrough assumes that the latest version of Xamarin.Android isinstalled and running on your platform of choice. For a guide toinstalling Xamarin.Android, refer to theXamarin.Android Installation guides.

Configuring emulators

If you are using the Android emulator, we recommend that you configurethe emulator to use hardware acceleration. Instructions for configuringhardware acceleration are available inHardware Acceleration for Emulator Performance.

Create the project

Start Visual Studio. Click File > New > Project to create a new project.

In the New Project dialog, click the Android App template.Name the new project Phoneword and click OK:

In the New Android App dialog, click Blank App and click OKto create the new project:

Create a layout

Tip

Newer releases of Visual Studio support opening .xml files inside the Android Designer.

Both .axml and .xml files are supported in the Android Designer.

After the new project is created, expand the Resourcesfolder and then the layout folder in the Solution Explorer.Double-click activity_main.axml to open it in the Android Designer. Thisis the layout file for the app's screen:

Tip

Newer releases of Visual Studio contain a slightly different app template.

  1. Instead of activity_main.axml, the layout is in content_main.axml.
  2. The default layout will be a RelativeLayout. For the rest of the steps on this page to workyou should change the <RelativeLayout> tag to <LinearLayout> and add another attributeandroid:orientation='vertical' to the LinearLayout opening tag.

From the Toolbox (the area on the left), enter text into the searchfield and drag a Text (Large) widget onto the design surface(the area in the center):

With the Text (Large) control selected on the design surface,use the Properties pane to change the Text property ofthe Text (Large) widget to Enter a Phoneword::

Drag a Plain Text widget from the Toolbox to the design surfaceand place it underneath the Text (Large) widget. Placement of thewidget will not occur until you move the mouse pointer to a place inthe layout that can accept the widget. In the screenshots below, thewidget cannot be placed (as seen on the left) until the mouse pointeris moved just below the previous TextView (as shown on the right):

Develop Android App On Mac

When the Plain Text (an EditText widget) is placed correctly, itwill appear as illustrated in the following screenshot:

With the Plain Text widget selected on the design surface,use the Properties pane to change the Id property of thePlain Text widget to @+id/PhoneNumberText and change theText property to 1-855-XAMARIN:

Drag a Button from the Toolbox to the designsurface and place it underneath the Plain Text widget:

With the Button selected on the design surface, use theProperties pane to change its Text property to Translate andits Id property to @+id/TranslateButton:

Drag a TextView from the Toolbox to the design surface andplace it under the Button widget. Change the Text property of theTextView to an empty string and set its Id property to@+id/TranslatedPhoneword:

Save your work by pressing CTRL+S.

Write some code

The next step is to add some code to translate phone numbers fromalphanumeric to numeric. Add a new file to the project byright-clicking the Phoneword project in the SolutionExplorer pane and choosing Add > New Item... as shown below:

In the Add New Item dialog, select Visual C# > Code > Code Fileand name the new code file PhoneTranslator.cs:

This creates a new empty C# class. Insert the following code into this file:

Save the changes to the PhoneTranslator.cs file by clickingFile > Save (or by pressing CTRL+S), then close the file.

Wire up the user interface

The next step is to add code to wire up the user interface by insertingbacking code into the MainActivity class. Begin by wiring up theTranslate button. In the MainActivity class, find the OnCreatemethod. The next step is to add the button code inside OnCreate,below the base.OnCreate(savedInstanceState) andSetContentView(Resource.Layout.activity_main) calls. First, modify thetemplate code so that the OnCreate method resembles the following:

Get a reference to the controls that were created in the layoutfile via the Android Designer. Add the following code inside theOnCreate method, after the call to SetContentView:

Add code that responds to user presses of the Translate button.Add the following code to the OnCreate method (after the linesadded in the previous step):

Save your work by selecting File > Save All (or bypressing CTRL-SHIFT-S) and build the application by selectingBuild > Rebuild Solution (or by pressing CTRL-SHIFT-B).

If there are errors, go through the previous steps and correct anymistakes until the application builds successfully. If you get abuild error such as, Resource does not exist in the currentcontext, verify that the namespace name in MainActivity.csmatches the project name (Phoneword) and then completely rebuildthe solution. If you still get build errors, verify that you haveinstalled the latest Visual Studio updates.

Set the app name

You should now have a working application – it's time to set thename of the app. Expand the values folder (inside the Resourcesfolder) and open the file strings.xml. Change the app name stringto Phone Word as shown here:

Run the app

Test the application by running it on an Android device or emulator.Tap the TRANSLATE button to translate 1-855-XAMARIN into aphone number:

To run the app on an Android device, see how to set up your device for development.

Launch Visual Studio for Mac from the Applications folder or fromSpotlight.

Click New Project... to create a new project.

In the Choose a template for your new project dialog, clickAndroid > App and select the Android App template. ClickNext.

In the Configure your Android app dialog, name the new app Phoneword and click Next.

In the Configure your new Android App dialog, leave the Solutionand Project names set to Phoneword and click Create to createthe project.

Create a layout

Tip

Newer releases of Visual Studio support opening .xml files inside the Android Designer.

Both .axml and .xml files are supported in the Android Designer.

After the new project is created, expand the Resources folderand then the layout folder in the Solution pad.Double-click Main.axml to open it in the Android Designer. Thisis the layout file for the screen when it is viewed in the Android Designer:

Select the Hello World, Click Me!Button on the designsurface and press the Delete key to remove it.

From the Toolbox (the area on the right), enter text into the search field and drag a Text (Large) widget onto the design surface (the area in the center):

With the Text (Large) widget selected on the design surface, youcan use the Properties pad to change the Text property of theText (Large) widget to Enter a Phoneword: as shown below:

Next, drag a Plain Text widget from the Toolbox tothe design surface and place it underneath the Text (Large)widget. Notice that you can use the search field to help locatewidgets by name:

With the Plain Text widget selected on the design surface, youcan use the Properties pad to change the Id property of thePlain Text widget to @+id/PhoneNumberText and change theText property to 1-855-XAMARIN:

Drag a Button from the Toolbox to the design surfaceand place it underneath the Plain Text widget:

With the Button selected on the design surface, you can use theProperties pad to change the Id property of the Button to@+id/TranslateButton and change the Text property to Translate:

Drag a TextView from the Toolbox to the design surface and place it under the Button widget. With the TextView selected, set the id property of the TextView to @+id/TranslatedPhoneWord and change the text to an empty string:

Save your work by pressing ⌘ + S.

Write some code

Mac

Now, add some code to translate phone numbers fromalphanumeric to numeric. Add a new file to the project byclicking the gear icon next to the Phoneword project in theSolution pad and choosing Add > New File...:

In the New File dialog, select General > Empty Class, name the new file PhoneTranslator, and click New. This creates a new empty C# class for us.

Remove all of the template code in the new class and replace it with the following code:

Save the changes to the PhoneTranslator.cs file bychoosing File > Save (or by pressing ⌘ + S), thenclose the file. Ensure that there are no compile-time errors byrebuilding the solution.

Wire up the user interface

The next step is to add code to wire up the user interface byadding the backing code into the MainActivity class.Double-click MainActivity.cs in the Solution Pad to open it.

Develop Android App With Python

Begin by adding an event handler to the Translate button. In theMainActivity class, find the OnCreate method. Add the button codeinside OnCreate, below the base.OnCreate(bundle) andSetContentView (Resource.Layout.Main) calls. Remove any existingbutton handling code (i.e., code that references Resource.Id.myButtonand creates a click handler for it) so that the OnCreate methodresembles the following:

Next, a reference is needed to the controls that were created inthe layout file with the Android Designer. Add the followingcode inside the OnCreate method (after the call toSetContentView):

Add code that responds to user presses of the Translate buttonby adding the following code to the OnCreate method (after thelines added in the last step):

Save your work and build the application by selecting Build > Build All(or by pressing ⌘ + B). If the applicationcompiles, you will get a success message at the top of Visual Studio for Mac:

If there are errors, go through the previous steps andcorrect any mistakes until the application builds successfully. Ifyou get a build error such as, Resource does not exist in thecurrent context, verify that the namespace name inMainActivity.cs matches the project name (Phoneword) and thencompletely rebuild the solution. If you still get build errors,verify that you have installed the latest Xamarin.Android andVisual Studio for Mac updates.

Set the label and app icon

Now that you have a working application, it's time to add thefinishing touches! Start by editing the Label for MainActivity.The Label is what Android displays at the top of the screen tolet users know where they are in the application. At the top of theMainActivity class, change the Label to Phone Word as shownhere:

Now it's time to set the application icon. By default, Visual Studio for Mac will provide a default icon for the project. Delete these files from the solution, and replace them with a different icon. Expand the Resources folder in the Solution Pad. Notice that there are five folders that are prefixed with mipmap-, and that each of these folders contains a single Icon.png file:

It is necessary to delete each of these icon files from the project. Right click on each of Icon.png files, and select Remove from the context menu:

Click on the Delete button in the dialog.

Next, download and unzip Xamarin App Icons set. This zip file holds the icons for the application. Each icon is visually identical but at different resolutions it renders correctly on different devices with different screen densities. The set of files must be copied into the Xamarin.Android project. In Visual Studio for Mac, in the Solution Pad, right-click the mipmap-hdpi folder and select Add > Add Files:

From the selection dialog, navigate to the unzipped Xamarin AdApp Icons directory and open the mipmap-hdpi folder. Select Icon.png and click Open.

In the Add File to Folder dialog box, select Copy the file into the directory and click OK:

Repeat these steps for each of the mipmap- folders until the contents of the mipmap- Xamarin App Icons folders are copied to their counterpart mipmap- folders in the Phoneword project.

After all the icons are copied to the Xamarin.Android project, open the Project Options dialog by right clicking on the project in the Solution Pad. Select Build > Android Application and select @mipmap/icon from the Application icon combo box:

Run the app

Finally, test the application by running it on an Android device or emulator and translating a Phoneword:

To run the app on an Android device, see how to set up your device for development.

Building Android App With Machine Learning

Congratulations on completing your first Xamarin.Android application!Now it's time to dissect the tools and skills you have just learned. Next up is theHello, Android Deep Dive.

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