如果给定参数失败，我敢打赌它是一个.请尝试格式化您的代码，如下所示:

I bet it''s one if the given arguments that fail. Please try to format your code like this:

double dUnitSize = Double.parseDouble(unitSize.getText().toString());
double dValue = calculate(
      firstUnit.getSelectedItem().toString(),
      secondUnit.getSelectedItem().toString(),
      dUnitSize
);
answer.setText(dValue);

您很快就会发现问题所在.

you''ll soon find out which line the problem is.