c# - enable a button when user starts typing wpf

Question

I have 3 text boxes and a search button.

<TextBox Grid.Row="1" Grid.ColumnSpan="2" VerticalAlignment="Center" HorizontalAlignment="Stretch" Text="{Binding Id, Mode=TwoWay}"/>
<TextBox Grid.Row="3" Grid.ColumnSpan="2" VerticalAlignment="Center" HorizontalAlignment="Stretch" Text="{Binding Name, Mode=TwoWay}"/>
<TextBox Grid.Row="5" Grid.ColumnSpan="2" VerticalAlignment="Center" HorizontalAlignment="Stretch" Text="{Binding Phone, Mode=TwoWay}"/>
<Button Grid.Row="8" Grid.ColumnSpan="2" Content="Search" Command="{Binding SearchPerson}" />

I have implemented logic where the user types something in any of the textboxes, then leaves the text box, at which point the search button gets enabled.

But, I want the search button to be enabled when a user "starts typing" (the string should not be null or whitespace) in any of the text boxes.

How do i implement this??

Many thanks in advance...

Answer 1

如果您希望在键入时更新源，则需要将绑定上的UpdateSourceTrigger属性设置为。PropertyChanged

因此，将您的绑定更改为：

Text="{Binding Id, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
Text="{Binding Name, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
Text="{Binding Phone, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"

Answer 2

好的，只需将我的评论转换为答案。

如MSDN Docs中所述

TextBox.Text 属性的默认 UpdateSourceTrigger 值为 LostFocus。

因此，要使其“尽快”，您只需要显式打开UpdateSourceTrigger=PropertyChanged绑定TextBox.Text即可。

像（在每个TextBox）：

Text="{Binding Id, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"

Answer 3

为什么不使用简单的 TextBox->OnTextChange 事件：

button1.IsEnabled = !string.IsNullOrWhiteSpace((sender as TextBox).Text);