.net Windows 窗体的 CheckBox CheckedChanged 与 CheckStateChanged

Windows Forms' CheckBox CheckedChanged vs. CheckStateChanged

提问by BojanG

Windows Forms' CheckBoxcontrol implements both CheckedChangedand CheckStateChangedevents. As far as I can tell, both fire when the checked status of the checkbox is changed.

Windows 窗体的CheckBox控件同时实现CheckedChanged和CheckStateChanged事件。据我所知，当复选框的选中状态发生变化时，两者都会触发。

CheckedChangedprecedes CheckStateChanged, but other than that I see no difference. Am I missing something? Should one be preferred over another?

CheckedChanged先于CheckStateChanged，但除此之外，我看不出有什么区别。我错过了什么吗？一个应该优先于另一个吗？

采纳答案by Jacob G

My guess would be that it has to do with tri-state checkboxes. This is the guts of the CheckState setter:

我的猜测是它与三态复选框有关。这是 CheckState setter 的核心：

 if (this.checkState != value)
 {
   bool flag = this.Checked;
   this.checkState = value;
   if (base.IsHandleCreated)
   {
     base.SendMessage(0xf1, (int) this.checkState, 0);
   }
   if (flag != this.Checked)
   {
     this.OnCheckedChanged(EventArgs.Empty);
   }
   this.OnCheckStateChanged(EventArgs.Empty);
 }

回答by stuartd

CheckState (and thus CheckStateChanged) allow for using a checkbox that can have three values: it can be checked, unchecked or 'indeterminate' - i.e. it has ThreeStateset to true.

CheckState（以及 CheckStateChanged）允许使用具有三个值的复选框：它可以被选中、未选中或“不确定”——即它的ThreeState设置为 true。

If you're not using ThreeState, then CheckedChanged is all you need.

如果您不使用 ThreeState，那么 CheckedChanged 就是您所需要的。

回答by Dave Cousineau

The two events are effectively the same unless you set the ThreeStateproperty to true. Without having set ThreeState, both will fire when the check box is checked or unchecked and both will fire afterthe value has changed.

除非您将ThreeState属性设置为 ，否则这两个事件实际上是相同的true。如果没有设置ThreeState，则在选中或取消选中复选框时两者都会触发，并且在值更改后两者都会触发。

The main difference is when you do set ThreeStateto true, which adds the IndeterminateCheckState:

主要区别在于当您设置ThreeState为 true 时，它​​会添加IndeterminateCheckState：

• The control considers Indeterminateto be "checked". (Checked == true).
• Transitioning between Checkedand Uncheckedis the same as before.
• Transitioning between Checkedand Indeterminatedoes notfire the CheckedChangedevent, because Checkedstays true.
• Transitioning between Uncheckedand Indeterminatedoesfire the CheckedChangedevent, because Checkedchanges from falseto trueor vice-versa.
• Clicking on a three state checkbox, the states transition from Uncheckedto Checkedto Indeterminateand back to Unchecked. You can still transition from Uncheckedto Indeterminateprogrammatically.

• 控件认为Indeterminate已“检查”。( Checked == true).
• 在Checked和之间的转换与Unchecked以前相同。
• 之间的转换Checked，并Indeterminate没有不火的CheckedChanged事件，因为Checked住宿true。
• 在Unchecked和之间转换Indeterminate确实会触发CheckedChanged事件，因为Checked从false到true或反之亦然。
• 点击一个三个态复选框，从美国过渡Unchecked到Checked以Indeterminate再换Unchecked。您仍然可以Unchecked以Indeterminate编程方式从 过渡到。

(Note the difference between the Checkedproperty, which is a two state boolean property, and the Checkedstate, which is one of the three possible values of the CheckStateproperty.)

（注意Checked属性是两个状态的布尔属性，Checked状态是CheckState属性的三个可能值之一。）

TL;DR: The main practical difference is that the CheckedChangedevent doesn't fire on a three state checkbox when transitioning from CheckState.Checkedto CheckState.Indeterminateor vice-versa, because both states are considered to be checked (Checked == true).

TL;DR：主要的实际区别是，在CheckedChanged从CheckState.Checkedto转换CheckState.Indeterminate或反之亦然转换时，事件不会在三态复选框上触发，因为这两种状态都被视为已选中 ( Checked == true)。

回答by John Line

As far as I can tell:

据我所知：

CheckChangedis fired BEFORE the checked value is changed, so .Checkedreturns what the value WAS,

CheckChanged在检查值更改之前被触发，因此.Checked返回值是什么，

CheckStateChangedis fired AFTER the checked value is changed, so .Checkedreturns what the value IS

CheckStateChanged在检查值更改后触发，因此.Checked返回值是什么

回答by TWood

CheckState fires before the new value is committed. CheckStateChanged fires after the new value is committed.

CheckState 在提交新值之前触发。CheckStateChanged 在提交新值后触发。

If your looking for dataset.haschanges to do an update after a checkbox value modification you need to use checkstatechanged event. Just make sure to disable threestate to keep from issues with NULL getting in there.

如果您正在寻找 dataset.haschanges 在复选框值修改后进行更新，您需要使用 checkstatechanged 事件。只需确保禁用三态以防止出现 NULL 问题。