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Mar 21 2018

Android Calculator Tutorial: Creating an Calculator App

#android #app #development #language


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Android Calculator Tutorial: Creating an Calculator App

Introduction

While creating the tutorial I assumed that the viewer already has a good understand of the Java language. This tutorial is a great way to see how a simple application can be so useful.

Here’s the code for the xmls and java files:

Stays the same just be wary of package names here as this one may differ to yours now if you used the previous code.

Note. My calc.xml is named activity_main.xml in this new example but I’ll point that out to you later, it doesn’t make much difference once you are aware of it.

Basically here we create a new row of buttons, backspace (bsp), dot (.) and 2 blank un-functioning buttons as seen from the highlighted code above and the graphic below.

Graphic Layout looks like this once all code is added:

Figure 1. Calculator design

Listing 4. Strings.xml

From the above code we can see the additions of backspace, dot, blank and blank2.

Okay, from the code above we have modified it so we can add extra functionality. See the highlighted text for reference and feel free to copy and paste it into your project. Not all changes are highlighted as they repeat themselves for different functionality in the code. We have declared a dot and backspace button, added their onclick listeners and added their functionality also.

With respect to the backspace button we used this code:

It basically gets the edit texts characters, if it’s greater than 0 we create a new string called newText consisting of String textInBox’s characters minus 1 character and assigns it to the display.

Adding the dot is like adding the numbers to the display, it’s the same principle. It’s functionality though requires the working out of decimals in our calculations.

So now we also have to accommodate for decimal numbers as integers will not suffice here. We did this by declaring op3 and op4, both doubles and modifying the code accordingly when carrying out the operations.

You can see where I blanked out the old code and put in the new above.

Just note my package name may differ from yours, so you will more than likely need to change it where necessary.

Listing 6. AndroidManifest.xml

Conclusion

You should now have the extra functionality of a decimal point button and a backspace button with the relevant fixes. It will now divide, multiply, subtract and add decimal values and also output a decimal answer for you. I hope this updated code is useful to you and I hope you enjoyed this answer. Happy coding 🙂


Steven Cronin

Has designed and developed several android applications from scratch which are available on Google Play.

What did you think of this post?

norman
Well done, everything is nice, but when I press one number and equal my program crashing.Could you help me with that? And one more thing, I press many numbers and the cursor goes first and when i press backspace the cursor stay first and the last number deletrs. But I want the cursor to appear last char. I appreciate your work.
[+1 year ago] Answer it

Brown Dw
This tutorial was very helpful to build my basics. I was able to build my own app for Play store. Thank you Sir. App Link. https://goo.gl/oMlqmn
[+1 year ago] Answer it

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