Tag Archives: selection

Adding radio buttons to an Android app with Xamarin

This tutorial explains how to add radio buttons to an Android app and make decisions based on which option the user selects. Radio buttons allow the user to select one item from a list of items. This is what an app screen with radio buttons looks like:

image10

Step 1

To get started, create a new Android app solution in Xamarin and then open the Main.axml file (in the Resources > layout folder). Drag a Text (Medium) element and three RadioButton elements from the Toolbox on to the app screen. Change the Text values on each element from the Properties panel and make sure each radio button has a name (eg. radioButton1, radioButton2, radioButton3) after @+id/ in the Id field on the Properties panel.

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Step 2

Add a Space element and another Text (Medium) element to your screen. Resize the Space element to make some space between the radio buttons and the Text (Medium) element. Give the Text (Medium) element a name eg @+id/resultTextView.

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Step 3

Open the MainActivity.cs file and define the three radio buttons and the text view. Then add them to the OnCreate method, so they can be accessed by the code.

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Step 4 

Now add a click event for each radio button so that the app displays a message saying which option was selected.

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Save your code and test the app. The example shown below is what you should see. However, the problem is that once you select an option it can’t be de-selected. Also, when using radio buttons you should only be able to select one option at a time but at the moment you can have more than one option selected at a time. We will fix this in the next section.

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Step 5

Go back to the screen design and delete all three radio buttons. Replace these radio buttons with a RadioGroup from the toolbox. This RadioGroup element has the name @+id/radioGroup1 . You will notice that the RadioGroup provides you already with three radio buttons grouped together. A RadioGroup can have any amount of radio buttons in it, but only one can be selected at a time.

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If you go to the Source view you can see that you can add more RadioButton elements to belong to the RadioGroup as long as you add them inside the RadioGroup tags.

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Change the Text value on each RadioButton so they are different.

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Step 6

Save the Main.axml file and go back to the MainActivity.cs file. The code needs to be changed so now it can access the RadioGroup element. A CheckChanged event is also added to detect when an option has been checked by the user. When this event fires, the option they selected is store in the option variable and the result is displayed to the user.

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Now if you test your app, it should look like what you see below. You could now add if statements to check which radio button was selected and have another event occur.

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Else and else if statements in PHP

In the previous tutorial we looked at if statements in PHP. In this tutorial we will look at how to specify more conditions by using the else and else if statements. If you are testing multiple conditions you can use an if statement along with else if and else statements. You can also place an if statement inside another if statement – this is known as a nested if statement.

The basic structure of if, else if and else statements looks like this:

if(condition){
  // do something
}
else if(another condition){
  // do something else
}
else{
  // do something completely different if the
  // other two conditions are not met
}

The basic structure of a nested if statement looks like this:

if(condition){
  if(another condition){
     //do something
  }
}

Make sure you use the correct brackets for conditions and statements inside if statements, and also make sure that you have matching closing brackets.

Watch the video below to see how to use if, else if, and else statements in PHP and then scroll down to see the sample code.

Sample PHP code:

<?php
 
 $age = 20;
 
 if($age >= 18){
 echo "You are old enough to vote";
 }
 
 else if($age == 17){
 echo "You can vote on your next birthday";
 }
 
 else{
 echo "You are not old enough to vote";
 }
 
?>

PHP Manual references:

Switch Statements in JavaScript

Switch statements are similar to ‘If’ statements but they are neater when working with many conditions. This video tutorial explains how to use switch statements. View it below or click here to view it on YouTube.

A switch statement is like an IF statement but is neater when working with many conditions.

Make sure you use the break statement at the end of each case so that the code runs efficiently. If you don’t use the break statement, the program will keep checking through all conditions even if a match has already been found. If none of the conditions are met, then the default case will run.

Take a look at the source code below and try using it in your own program.

<!DOCTYPE html>
<html lang="en">
<head>
 <meta charset="utf-8"/>
 <title>JavaScript - Switch Statements</title>
 <script type="text/javascript">
 
 // A switch statement is like an IF statement but is neater when working with many conditions.
 // Use the break statement at the end of each case so that the code runs efficiently.
 // If you don't use break, the program which keep checking through all conditions even if a match has
 // already been found. If none of the conditions are met, then the 'default' case will run.
 
 var city="Sydney";
 
 switch(city){
 case "Melbourne":
 document.write("You are from Melbourne");
 break;
 case "Sydney":
 document.write("You are from Sydney");
 break;
 case "Perth":
 document.write("You are from Perth");
 break;
 case "Brisbane":
 document.write("You are from Brisbane");
 break;
 default:
 document.write("You don't live in a city I recognise.");
 }
 
 
 </script>
 
</head>
<body>
 
</body>
</html>

Next tutorial: While loops

How to make a transparent background for an image in Photoshop CC

This video tutorial explains how to make a transparent background in Adobe Photoshop CC. You might have a shape or text in an image with a white background that you want to make transparent, or you might have an image that you want to make certain parts of transparent. This video explains how! You can watch it below or click here to view it on YouTube.