如何从Android中的TextView中删除最后一个字符？

我正在为一个班级创建一个计算器应用程序，并且除“ BackSpace”按钮外，其他所有功能都可以正常工作。关于操作TextView的唯一信息是使用SetText方法将TextView重置为null或仅是一个空字符串。我需要做的是删除输入到计算器中的最后一个数字，例如：如果输入数字12并按退格键，它将删除数字2，但保留数字1。我决定只包括“ onClick”方法作为与此问题相关的唯一方法，所有计算都以另一种方法完成。谢谢！

 public void onClick(View v) {

        // display is assumed to be the TextView used for the Calculator display
        String currDisplayValue = display.getText().toString();

        Button b = (Button)v;  // We assume only buttons have onClickListeners for this App
        String label = b.getText().toString();  // read the label on the button clicked

        switch (v.getId())
        {
            case R.id.clear:
                calc.clear();
               display.setText("");
                //v.clear();
                break;
            case R.id.plus:
            case R.id.minus:
            case R.id.mult:
            case R.id.div:
                String operator = label;
                display.setText("");
                calc.update(operator, currDisplayValue);

                break;
            case R.id.equals:
              display.setText(calc.equalsCalculation(currDisplayValue));
                break;

            case R.id.backSpace:
                // Do whatever you need to do when the back space button is pressed
                //Removes the right most character ex: if you had the number 12 and pressed this button
                //it would remove the 2. Must take the existing string, remove the last character and
                //pass the new string into the display.

                display.setText(currDisplayValue);
                break;
            default:
                // If the button isn't one of the above, it must be a digit
                String digit = label;// This is the digit pressed
                display.append(digit);
                break;
        }
    }