如何获得的DropDownList的previous项目之前OnSelectedIndexChanged触发事件 [英] How to get the previous item on DropDownList before OnSelectedIndexChanged fires the event

问题描述

我将如何前 OnSelectedIndexChanged 获得的DropDownList 的previous项目引发事件？

How would I get the previous item on DropDownList before OnSelectedIndexChanged fires the event?

例子：我有一个的DropDownList 有名称作为其项目（约翰福音，马）。默认情况下，的SelectedIndex 是约翰。一旦改变其索引，然后选择标记事件 OnSelectedIndexChanged 将被触发。当我使用 ddlName.SelectedIndex 将用于马克，我希望得到的是约翰的索引只返回指数。

Example: I had a DropDownList that has names as its items ("John", "Mark"). By default the SelectedIndex is "John". Upon changing its index and selecting "Mark" the event OnSelectedIndexChanged will be triggered. When I use ddlName.SelectedIndex it will return only the index for "Mark" which I want to get is the index of "John".

推荐答案

您不能捕获事件之前的变化，但是你可以很容易地存储在一个变量previous值。每一次的SelectedIndexChanged被激发，使用previous值，然后将其设置为新指数（下一次的事件触发的）。为了处理这种情况时，它是一个新的选择（从默认的），你可以设置变量在页面加载时，或者允许它为空，并有提醒用户注意的事实，这是一个新的选择（然后你​​就可以处理但是你喜欢）。

You can't capture an event prior to the change, but you could easily store the previous value in a variable. Each time SelectedIndexChanged is fired, use the previous value and then set it to the new index (for the next time the event fires). To handle the case when it's a new selection (from the default), you can either set the variable when the page loads, or allow it to be null and have that alert you to the fact it's a new selection (which you can then handle however you like).

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