TOC

This article is currently in the process of being translated into Czech (~25% done).

Základní ovládací prvky ("Controls"):

The CheckBox control

Komponenta CheckBox dovoluje konečnému uživateli přepnout volbu na zapnuto/vypnuto, obvykle odrážející Boolean hodnotu v Code-Behind (.cs - pozn. překladatele). Pojďme rovnou na příklad, pokud si nejste jistí, jak CheckBox vypadá:

<Window x:Class="WpfTutorialSamples.Basic_controls.CheckBoxSample"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="CheckBoxSample" Height="140" Width="250">
    <StackPanel Margin="10">
		<Label FontWeight="Bold">Application Options</Label>
		<CheckBox>Enable feature ABC</CheckBox>
		<CheckBox IsChecked="True">Enable feature XYZ</CheckBox>
		<CheckBox>Enable feature WWW</CheckBox>
	</StackPanel>
</Window>

Jak můžete vidět, CheckBox je velice stadné používat. V druhém CheckBoxu jsem použil vlastnost IsChecked abych měl defaultně zaškrtlý CheckBox, ale kromě toho nejsou potřeba žádné jiné vlastnosti k užívání. Pokud chcete kontrolovat zda je CheckBox zaškrtnutý či ne, můžete použít vlastnost IsChacked také z Code-behind.

Custom content

The CheckBox control inherits from the ContentControl class, which means that it can take custom content and display next to it. If you just specify a piece of text, like I did in the example above, WPF will put it inside a TextBlock control and display it, but this is just a shortcut to make things easier for you. You can use any type of control inside of it, as we'll see in the next example:

<Window x:Class="WpfTutorialSamples.Basic_controls.CheckBoxSample"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="CheckBoxSample" Height="140" Width="250">
    <StackPanel Margin="10">
		<Label FontWeight="Bold">Application Options</Label>
		<CheckBox>
			<TextBlock>
				Enable feature <Run Foreground="Green" FontWeight="Bold">ABC</Run>
			</TextBlock>
		</CheckBox>
		<CheckBox IsChecked="True">
			<WrapPanel>
				<TextBlock>
					Enable feature <Run FontWeight="Bold">XYZ</Run>
				</TextBlock>
				<Image Source="/WpfTutorialSamples;component/Images/question.png" Width="16" Height="16" Margin="5,0" />
			</WrapPanel>
		</CheckBox>
		<CheckBox>
			<TextBlock>
				Enable feature <Run Foreground="Blue" TextDecorations="Underline" FontWeight="Bold">WWW</Run>
			</TextBlock>
		</CheckBox>
	</StackPanel>
</Window>

As you can see from the sample markup, you can do pretty much whatever you want with the content. On all three check boxes, I do something differently with the text, and on the middle one I even throw in an Image control. By specifying a control as the content, instead of just text, we get much more control of the appearance, and the cool thing is that no matter which part of the content you click on, it will activate the CheckBox and toggle it on or off.

The IsThreeState property

Jak bylo zmíněno, CheckBox zpravidla odpovídá hodnotě boolean, která znamená, že má jen dva stavy: true nebo false (pravda, nepravda / zapnuto, vypnuto). Nicméně od té doby, co datový typ boolean může být "nulovatelný", je fakticky přidaná třetí možtnost (true, false nebo null), CheckBox také podporuje tuto možnost. Pomocí nastavení vlastnosti IsThreeState na "true" bude CheckBox mít třetí stav zvaný "neurčitý stav".

A common usage for this is to have a "Enable all" CheckBox, which can control a set of child checkboxes, as well as show their collective state. Our example shows how you may create a list of features that can be toggled on and off, with a common "Enable all" CheckBox in the top:

<Window x:Class="WpfTutorialSamples.Basic_controls.CheckBoxThreeStateSample"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="CheckBoxThreeStateSample" Height="170" Width="300">
	<StackPanel Margin="10">
		<Label FontWeight="Bold">Application Options</Label>
		<StackPanel Margin="10,5">
			<CheckBox IsThreeState="True" Name="cbAllFeatures" Checked="cbAllFeatures_CheckedChanged" Unchecked="cbAllFeatures_CheckedChanged">Enable all</CheckBox>
			<StackPanel Margin="20,5">
				<CheckBox Name="cbFeatureAbc" Checked="cbFeature_CheckedChanged" Unchecked="cbFeature_CheckedChanged">Enable feature ABC</CheckBox>
				<CheckBox Name="cbFeatureXyz" IsChecked="True" Checked="cbFeature_CheckedChanged" Unchecked="cbFeature_CheckedChanged">Enable feature XYZ</CheckBox>
				<CheckBox Name="cbFeatureWww" Checked="cbFeature_CheckedChanged" Unchecked="cbFeature_CheckedChanged">Enable feature WWW</CheckBox>
			</StackPanel>
		</StackPanel>
	</StackPanel>
</Window>
using System;
using System.Windows;

namespace WpfTutorialSamples.Basic_controls
{
	public partial class CheckBoxThreeStateSample : Window
	{
		public CheckBoxThreeStateSample()
		{
			InitializeComponent();
		}


		private void cbAllFeatures_CheckedChanged(object sender, RoutedEventArgs e)
		{
			bool newVal = (cbAllFeatures.IsChecked == true);
			cbFeatureAbc.IsChecked = newVal;
			cbFeatureXyz.IsChecked = newVal;
			cbFeatureWww.IsChecked = newVal;
		}

		private void cbFeature_CheckedChanged(object sender, RoutedEventArgs e)
		{
			cbAllFeatures.IsChecked = null;
			if((cbFeatureAbc.IsChecked == true) && (cbFeatureXyz.IsChecked == true) && (cbFeatureWww.IsChecked == true))
				cbAllFeatures.IsChecked = true;
			if((cbFeatureAbc.IsChecked == false) && (cbFeatureXyz.IsChecked == false) && (cbFeatureWww.IsChecked == false))
				cbAllFeatures.IsChecked = false;
		}

	}
}

This example works from two different angles: If you check or uncheck the "Enable all" CheckBox, then all of the child check boxes, each representing an application feature in our example, is either checked or unchecked. It also works the other way around though, where checking or unchecking a child CheckBox affects the "Enable all" CheckBox state: If they are all checked or unchecked, then the "Enable all" CheckBox gets the same state - otherwise the value will be left with a null, which forces the CheckBox into the indeterminate state.

All of this behavior can be seen on the screenshots above, and is achieved by subscribing to the Checked and Unchecked events of the CheckBox controls. In a real world example, you would likely bind the values instead, but this example shows the basics of using the IsThreeState property to create a "Toggle all" effect.

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