android - datePicker.getMonth() +1 没有给出预期的结果

Question

             Toast.makeText(getBaseContext(),
            "Date selected:" + datePicker.getMonth()+1+
            "/"+ datePicker.getDayOfMonth() +
            "/"+ datePicker.getYear() +"\n" +
            "Time Slected:" + timePicker.getCurrentHour() + 
            ":"+ timePicker.getCurrentMinute(),
            Toast.LENGTH_SHORT).show();

通过将 1 加到 datePicker.getMonth()，我得到月份数

            output like->
            jan-01,feb-11,mar-21

但是当我删除“1”时，我得到的月份数字输出如下

            jan-0,feb-01,mar-02

Answer 1

你需要括号。

(datePicker.getMonth()+1)

否则你就是在进行字符串连接。

例如

如果 getMonth() 返回 0(一月)，则

"Date selected: " + datePicker.getMonth()+1

是

("Date selected: " + 0) + 1
= "Date selected: 0" + 1
= "Date selected: 01"

但是有 parent

"Date selected: " + (datePicker.getMonth()+1)
= "Date selected: " + (0+1)
= "Date selected: " + 1
= "Date selected: 1"