当用户单击加号按钮时，我如何每次加+30？

Question

For the first item the total is 49, but I want to add 30 every time the user clicks on the button.

1st item: 49
2nd item: 79
3rd item: 109

and so on.

I have tried this but it's not working:

for (int i =49;i<9;i=i+30) 
{
    price.setText("$" + Integer.toString(i));
}

Answer 1

if you want to do you work in loop then do it like this.

 int firstval = 49;
 for (int i = 0; i < 9; i++) {
      System.out.println(Integer.toString(firstval += 30));
 }

ans will be like this

I/System.out: 79
I/System.out: 109
I/System.out: 139
I/System.out: 169
I/System.out: 199
I/System.out: 229
I/System.out: 259
I/System.out: 289
I/System.out: 319

or if you want to do with button click then

int firstval = 49;
button.setOnClickListener(v -> incValue());
private void incValue() {
    System.out.println(Integer.toString(firstval += 30));
}

Answer 2

If you want to add 30 on clicking plus button, first you need to add an OnClickListner on Button , the implementation will depend on which language you are using and then the actual code can be highlighted.

You can get the actual value in the listener callback function and then just add your defined value and set it, why you need to use the loop

public static final Integer INC_FACTOR = 30; // Increment factor

public onClickListner(Button ref) { // some dummy onClickListner
    ref.setLabel(String.valueOf(Integer.parseInt(ref.getLabel())+ INC_FACTOR));
}

Answer 3

Something like this ?

public class counter {
    total = 0;

    userClicked() {
        total += 30;
    }
}