WPF 实现按钮的长按，短按功能

实现了一个支持长短按得按钮组件，单击可以触发Click事件，长按可以触发LongPressed事件，长按松开时触发LongClick事件。源码请自取：Github

长按阈值属性的建立

为了方便在xaml中使用，我们先配置一个DependencyProperty叫做LongPressTime来作为界定长按的阈值

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public class LongPressButtonEx : Button
{
        public static readonly DependencyProperty LongPressTimeProperty
            = DependencyProperty.Register("LongPressTime", typeof(int),
                typeof(LongPressButtonEx), new PropertyMetadata(500));

        public int LongPressTime
        {
            set => SetValue(LongPressTimeProperty, value);
            get => (int)GetValue(LongPressTimeProperty);
        }
}

定义完成后可以在Xaml设计器中使用LongPressTime这个拓展属性

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<Window x:Class="LongPressButton.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:LongPressButton"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <Grid>
        <local:LongPressButtonEx Width="96" Height="48" LongPressTime="200">
            Button
        </local:LongPressButtonEx>
    </Grid>
</Window>

长按的定时器判定方法

C#中的4种定时器，在WPF中需要使用Dispater Timer

定义一个DispatcherTimer来监控是否按下达到了长按

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private DispatcherTimer _pressDispatcherTimer;

private void OnDispatcherTimeOut(object sender, EventArgs e)
{
    _pressDispatcherTimer?.Stop();
    Debug.WriteLine($"Timeout {LongPressTime}");
}

protected override void OnMouseLeftButtonDown(MouseButtonEventArgs e)
{
    base.OnMouseLeftButtonDown(e);
    Debug.WriteLine("Button: Mouse down.");
    if (_pressDispatcherTimer == null)
    {
        _pressDispatcherTimer = new DispatcherTimer();
        _pressDispatcherTimer.Tick += OnDispatcherTimeOut;
        _pressDispatcherTimer.Interval = new TimeSpan(0, 0, 0, 0, LongPressTime);
        _pressDispatcherTimer.Start();
        Debug.WriteLine("Button: Timer started");
    }
}

protected override void OnMouseLeftButtonUp(MouseButtonEventArgs e)
{
    base.OnMouseLeftButtonUp(e);
    Debug.WriteLine("Button: Mouse up.");
    _pressDispatcherTimer?.Stop();
    _pressDispatcherTimer = null;
}

现在分别点击和长按按钮可以看到调试输出

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...
# 点击
Button: Mouse down.
Button: Timer started
Button: Mouse up.
# 长按
Button: Mouse down.
Button: Timer started
Timeout 200
Button: Mouse up.

实现长按事件的定义

现在作为一个自定义控件，我们需要在长按后发出一个RoutedEvent，并修改部分之前的代码抛出事件

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/// <summary>
/// LongPress Routed Event
/// </summary>
public static readonly RoutedEvent LongPressEvent
    = EventManager.RegisterRoutedEvent("LongPress",
        RoutingStrategy.Bubble,
        typeof(RoutedEventHandler),
        typeof(LongPressButtonEx));

public event RoutedEventHandler LongPress
{
    add => AddHandler(LongPressEvent, value);
    remove => RemoveHandler(LongPressEvent, value);
}

private void OnDispatcherTimeOut(object sender, EventArgs e)
{
    _pressDispatcherTimer?.Stop();
    Debug.WriteLine($"Timeout {LongPressTime}");
    RaiseEvent(new RoutedEventArgs(LongPressEvent));    // raise the long press event
}

回到窗体的代码中，添加事件的响应

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<local:LongPressButtonEx Height="48" Width="256" LongPressTime="200"
        LongPress="LongPressButtonEx_LongPress"
        Click="LongPressButtonEx_Click">
    Click or Long Press Me!
</local:LongPressButtonEx>

C#代码如下，长按按钮会显示Long Pressed，单击会是Click

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private void LongPressButtonEx_LongPress(object sender, RoutedEventArgs e)
{
    if (sender is LongPressButtonEx btn)
    {
        btn.Content = "Long Pressed";
    }
}

private void LongPressButtonEx_Click(object sender, RoutedEventArgs e)
{
    if (sender is LongPressButtonEx btn)
    {
        btn.Content = "Clicked";
    }
}

发现Click和LongPress都可以响应，但是当松开按钮时又变成了Click，原因是鼠标松开时响应了默认的Click事件

现在对按钮控件默认的OnClick函数稍作修改，可以让Click也不出问题

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/// <summary>
/// DependencyProperty for IsLongPress 
/// </summary>
public static readonly DependencyProperty IsLongPressProperty
    = DependencyProperty.Register("IsLongPress", typeof(bool),
        typeof(LongPressButtonEx), new PropertyMetadata(false));

public bool IsLongPress
{
    set => SetValue(IsLongPressProperty, value);
    get => (bool)GetValue(IsLongPressProperty);
}

private void OnDispatcherTimeOut(object sender, EventArgs e)
{
    IsLongPress = true;
    _pressDispatcherTimer?.Stop();
    Debug.WriteLine($"Timeout {LongPressTime}");
    RaiseEvent(new RoutedEventArgs(LongPressEvent));    // raise the long press event
}

protected override void OnClick()
{
    if (!IsLongPress)
    {
        base.OnClick();
    }
    else
    {
        RaiseEvent(new RoutedEventArgs(LongPressReleaseEvent));    // raise the long press event
        IsLongPress = false;
    }
}