As @ScottWe提到：你试图在HTML / javascript中应用PLSQL逻辑。 'When - Condition'在运行时被评估，因此你不能在那里使用PLSQL。
日期算术在JavaScript中有点恼人，所以如果你不熟悉，这里是一种方式可以执行你的支票（即是明天的输入日期）。

从我的线索：

Javascript中的日期差异（忽略一天中的时间）

JavaScript如何以dd-mm-yy格式获取明天日期

将这个函数添加到页面的JavaScript部分，以获取全局变量和函数：

  function isTomorrow（pDateItem）{
 function getTomorrow（）{
 var tomorrow = new Date（）; 
 tomorrow.setDate（tomorrow.getDate（）+ 1）; 
明天回来
}; 

函数cutTime（pDate）{
返回新日期（pDate.getFullYear（），pDate.getMonth（），pDate.getDate（））; 
}; 

 //检查pDateItem是否导致选择
 //检查是否是datepicker 
 //检查是否已选择日期
 if（$（ pDateItem）.length 
&&$（pDateItem）.data（datepicker）
&& $（pDateItem）.datepicker（getDate）！== null 
 ）
 {
 var tomorrow = getTomorrow（）; 
 var check = $（pDateItem）.datepicker（getDate）; 
 var one = cutTime（check）; 
 var two = cutTime（tomorrow）; 

 return one.getDate（）=== two.getDate（）; 
}; 
返回false; 
} 
 

然后在动态动作When条件下，使用一个javascript表达式代码：

  isTomorrow（this.triggeringElement）
 

然后，当日期设置为明天时，相应的True Actions才会触发。

I have a date picker where the user simply chooses a date then a Dynamic Action is suppose to send an alert if the user clicks tomorrow(sysdate+1).

The Datepicker term is the simple layout.

The Dynamic Action-->

Name: Valid Date

Event: Change

Selection type: Item(s)

Item(s): datepicker_name

Condition: equal to

Value: sysdate+1

When I run the program and click any day on the calendar, no alert comes up. I thought the problem was the format. The Dynamic Action sees the date as "DD/MM/YYYY" while the Datepickers output is "DD-Mon-YY" so it could not compare them. Apples and Oranges. But I played around with the format to make it all the same but still no progress.

Thanks again for your time and help!

As @ScottWe mentions: you're trying to apply PLSQL logic in HTML/javascript. The 'When - Condition' is evaluated at runtime and thus you can't use PLSQL there. The date arithmetic is a bit annoying in javascript though, so if you're a unfamiliar with it, here is a way you can perform your check (which is, is the entered date tomorrow or not).

Taking my clues from these:
Date difference in Javascript (ignoring time of day)
JavaScript how to get tomorrows date in format dd-mm-yy

Add this function to the page's javascript section for global variables and functions:

function isTomorrow(pDateItem){  
  function getTomorrow(){ 
    var tomorrow = new Date();
    tomorrow.setDate(tomorrow.getDate() + 1);
    return tomorrow;
  };

  function cutTime(pDate){
    return new Date(pDate.getFullYear(), pDate.getMonth(), pDate.getDate());
  };

  // check if pDateItem leads to a selection
  // check if it is a datepicker
  // check if a date has been selected
  if ( $(pDateItem).length 
       && $(pDateItem).data("datepicker")
       && $(pDateItem).datepicker("getDate") !== null 
     ) 
  {        
    var tomorrow = getTomorrow();
    var check = $(pDateItem).datepicker("getDate");
    var one = cutTime(check);
    var two = cutTime(tomorrow);

    return one.getDate() === two.getDate();
  };
  return false;
}

Then in your Dynamic action 'When' condition, use a javascript expression with this code:

isTomorrow(this.triggeringElement)

Then the corresponding True Actions will only fire when the date is set to tomorrow.