vb.net 将 SelectedIndex 或 SelectedItem 用于 ComboBox 更好吗？
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Better to use SelectedIndex or SelectedItem for ComboBox?
提问by Stas Bukhtiyarov
Lets say I have a ComboBoxwith the values "One, Two, Three"
假设我有一个ComboBox值“一，二，三”
As a general rule, when testing for conditional events based on the ComboBoxselection, would it be better to reference the ComboBox.SelectedItem or ComboBox.SelectedIndex?
作为一般规则，在测试基于ComboBox选择的条件事件时，引用 ComboBox.SelectedItem 或 ComboBox.SelectedIndex 会更好吗？
If (ComboBox.SelectedItem = "One")
or
或者
If (ComboBox.SelectedIndex = 0)
Or does neither have an advantage over the other?
或者两者都没有比另一个优势？
回答by Steve
I find SelectedIndexeasier to use because you can work on a number and when there is no selection you don't have to handle the null. SelectedItem could be null and you should remember this when trying to access that property.
我发现SelectedIndex更容易使用，因为您可以处理一个数字，并且当没有选择时，您不必处理空值。SelectedItem 可能为 null，您应该在尝试访问该属性时记住这一点。
Usually SelectedItem and SelectedIndex are used inside a SelectedIndexChanged event and it easy to forget the Nothing possibility
通常 SelectedItem 和 SelectedIndex 在 SelectedIndexChanged 事件中使用，很容易忘记 Nothing 可能性
Dim curValue = Combo.SelectedItem.ToString() ' <- Possible NullReferenceException'
.....
However, if we are just talking about comparison then there is a very small advantage for SelectedIndex because there is no loading and testing of a string.
然而，如果我们只是在谈论比较，那么 SelectedIndex 有一个非常小的优势，因为没有加载和测试字符串。
ComboBox b = new ComboBox();
if(b.SelectedItem == "One")
Console.WriteLine("OK");
if(b.SelectedIndex == 0)
Console.WriteLine("OK");
IL Code
代码
IL_0000: newobj System.Windows.Forms.ComboBox..ctor
IL_0005: stloc.0 // b
IL_0006: ldloc.0 // b
IL_0007: callvirt System.Windows.Forms.ComboBox.get_SelectedItem
IL_000C: ldstr "One"
IL_0011: bne.un.s IL_001D
IL_0013: ldstr "OK"
IL_0018: call System.Console.WriteLine
IL_001D: ldloc.0 // b
IL_001E: callvirt System.Windows.Forms.ListControl.get_SelectedIndex
IL_0023: brtrue.s IL_002F
IL_0025: ldstr "OK"
IL_002A: call System.Console.WriteLine
But we are in the realm of micro-optimizations and, as said in a comment, use what is more readable for you.
但是我们处于微优化领域，正如评论中所说，使用对您来说更具可读性的内容。
回答by mfeingold
SelectedIndex is guaranteed to be unique, SelectedItem is not
SelectedIndex 保证是唯一的，SelectedItem 不是
