C#
PROJECT 1.2.3
Change colors
Mobile App (Android)
Part 1
For our projects we will use Microsoft Visual Studio 2019. It allows to create projects in different programming languages and on different platforms.
At the time of creating our resource, the functionality of Mobile app development tools in Visual Studio 2022 has not been fully developed by the Microsoft team, so we will use Visual Studio 2019.
Open Visual Studio 2019. Click Create a new project
From The first Lists choose C#. From the second Android, from the third Mobile . Click Android App (Xamarin)
Give the name of the Project MyFirstAndroidApp. Specify the destination folder address and click Create .
Select the Simple View App and click OK
Our Android App was created. Now we must move to the design view to create an app interface. In the Solution Explorer panel expand the folder list: Resources. After expand folder Layout, right-click on the file Activity_main.xml, and in the context menu click on View Designer.
The design view will open with our Android app interface.
Initially we have to create web app interface and add programming code to it.
Click the Tab MainActivity.cs to move to C# Code. Let's change our app label text to "My First Android app". this text will be on the head of our app when we run it.
In the case of mobile app development Visual Studio does not offer us as simple drag-and-drop functionality as in the case of desktop apps. First, we must think about Layouts. In the Toolbox panel click on the LinearLayout (Vertical) and dag-and-drope on the form.
Select LinearLayout and move the blue line up as in the next image. This will decrease the layout's vertical size (if you do not understand something from the text please watch the video).
Dag-and-drope 3 Buttons and one Plain Text from the Toolbox panel.
Now select button1 and from the Properties window change the property Text to 'RED", and change the text color: in the Properties window: expand Style, find Text Color, and click No brush. Select the red color from the palette.
Do the same for other buttons as well.
Now the interface is ready. Let's start coding.
Click the Tab MainActivity.cs to move to C# Code. copy and paste the next code See the next image.
C# Code
FindViewById<Button>(Resource.Id.button1).Click += (o, e) =>
{
FindViewById<LinearLayout>(Resource.Id.linearLayout1).SetBackgroundColor(Android.Graphics.Color.Red);
};
FindViewById<Button>(Resource.Id.button2).Click += (o, e) =>
{
FindViewById<LinearLayout>(Resource.Id.linearLayout1).SetBackgroundColor(Android.Graphics.Color.Blue);
};
FindViewById<Button>(Resource.Id.button3).Click += (o, e) =>
{
FindViewById<LinearLayout>(Resource.Id.linearLayout1).SetBackgroundColor(Android.Graphics.Color.Black);
};
Now we have to deploy the App to the Android mobile phone. Please connect your PC to the phone using the USB cable. To be able deploy the app to the Android phone first we have to enable developer options. Here is the link that will help you>>>
After the developer option is allowed you will see your phone name in the Visual Studio menu panel (after the green triangle button).
Click the green triangle button on the menu panel to deploy the App to the phone. After it is done the App will run on the phone.
Click the buttons "Red", "Blue" or "Black", and WOW! Your first Android application performs the tasks!
Part 2
Now let's make our app more diinamic. We want to change the screen color based on the text we will write in the textbox. If we write "Red" the Color must change to red, If the "Blue" color must be blue and if "black" the screen must become black.
For this we will use the if operator we learned in previous lessons.
if opeartor
Here is the C# syntax for the if operator:
--------------------------
if ( condition) {
operation(s)
}
--------------------------
Example:
if (FindViewById<EditText>(Resource.Id.editText1).Text == "red")
{
FindViewById<LinearLayout>(Resource.Id.linearLayout1).SetBackgroundColor(Android.Graphics.Color.Red);
}
Please use the Simulator to continue the tutorial...
Conclusion:
We have created our first Android application in the Visual Studio environment using the Android App (Xamarin). Initially, we created the interface (visual side), then we wrote the programming code in C#.
We deployed our app to the phone. For this we changed some phone parameters and connected the phone to the PC.