Very Simple Android App - MathSucks

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Just want to make a note for this very simple android app, which does percentages.

Even though this is super simple, I still had a problem when I run it😅. The problem I had is every TextView, Button, EditText aligned to top left side of the screen. I checked the property of them, all center, it is supposed to work.

Then, I realized the default layout is ConstraintLayout, and I tried to change it to RelativeLayout, every widget on the design screen went back to top left side. I dragged them back to the center, aligned them vertically, tried to run it. It worked~~~.

Code edited in MainActivity.java

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public class MainActivity extends AppCompatActivity {

    TextView totalTextView;
    EditText percentageTxt;
    EditText numberTxt;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        totalTextView = (TextView) findViewById(R.id.totalTextView);
        percentageTxt = (EditText) findViewById(R.id.percentageTxt);
        numberTxt = (EditText) findViewById(R.id.numberTxt);

        Button calcBtn = (Button) findViewById(R.id.calcBtn);
        calcBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick (View view) {
                float percentage = Float.parseFloat(percentageTxt.getText().toString());
                float dec = percentage / 100;
                float total = dec * Float.parseFloat(numberTxt.getText().toString());
                totalTextView.setText (Float.toString(total));
            }

        });
    }

Demo Screens
mathsucks
mathsucks1

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