The solution
would be to build your own control and use Touch.FrameReported to
“drive” it. In this sample I will build a multi-touch button. I will call it
ButtonEx (some of you remember OpenNETCF J
?) and I will just add three events to it: TouchDown, TouchUpInside, TouchUpOutSide (iOs
MonoTouch event names). With this three events I should have better control
(Click in reality is a TouchUpInside event) .
So I've created a
new Windows Phone Class Library called ControlsEx and I added the control
ButtonEx derived from ContentControl. I copied the standard style of the Button
control (you can easily generate it from a standard button using Blend and Edit
Copy command on the Button Template). I've then added the style to the /Themes/generic.xaml
file inside our project. When I create
the control I will subscribe Loaded and Unloaded events as I want to start
receiving Touch events when the control loads and unsubscribe the Touch events
when the control gets unloaded.
public ButtonEx()
{
DefaultStyleKey = typeof(ButtonEx);
this.Loaded += ButtonEx_Loaded;
this.Unloaded += ButtonEx_Unloaded;
IsEnabledChanged += ButtonEx_IsEnabledChanged;
IsPressed = false;
}
void ButtonEx_Loaded(object sender, RoutedEventArgs e)
{
Touch.FrameReported += Touch_FrameReported;
}
void ButtonEx_Unloaded(object sender, RoutedEventArgs e)
{
Touch.FrameReported -= Touch_FrameReported;
}
Now everything we need “happens” inside the Touch_FrameReported method. For my button I am interested to trace only one finger(using its id) from TouchAction.Down until TouchAction.Up. Once the first finger is down on the surface of my control I memorize the id and track it’s actions till it leaves the screen. Depending of the control that you are building you might have to take in consideration multiple fingers. One thing that is pretty important when starting to track a finger is to see if your control is in front or not (imagine an MessageBox over your controls and when you press the Ok button you will also press the button which is in the back). To resolve this issue I’ve used TouchDevice.DirectlyOver property of the TouchPoint and the VisualTreeHelper to see if the UIElement returned by DirectlyOver is a member of my control or not.
bool IsControlChild(DependencyObject element)
{
DependencyObject parent = element;
while ((parent != this) && (parent != null))
parent=VisualTreeHelper.GetParent(parent);
if (parent == this)
return true;
else
return false;
}
void Touch_FrameReported(object sender, TouchFrameEventArgs e)
{
if (Visibility == Visibility.Collapsed)
return;
TouchPointCollection pointCollection = e.GetTouchPoints(this);
for (int i = 0; i < pointCollection.Count; i++)
{
if (idPointer == -1)
{
if (IsEnabled&&(Visibility==Visibility.Visible) && (pointCollection[i].Action == TouchAction.Down) && IsControlChild(pointCollection[i].TouchDevice.DirectlyOver))
{
//start tracing this finger
idPointer = pointCollection[i].TouchDevice.Id;
IsPressed = true;
VisualStateManager.GoToState(this,"Pressed", true);
if (TouchDown != null)
TouchDown(this, pointCollection[i].Position);
}
}
else if ((pointCollection[i].TouchDevice.Id == idPointer) && (pointCollection[i].Action == TouchAction.Up))
{
idPointer =-1;
IsPressed = false;
UpdateIsEnabledVisualState();
if ((pointCollection[i].Position.X > 0 && pointCollection[i].Position.X < ActualWidth) && (pointCollection[i].Position.Y > 0 && pointCollection[i].Position.Y < ActualHeight))
{
if (TouchUpInside != null)
TouchUpInside(this, pointCollection[i].Position);
}
else
{
if (TouchUpOutside != null)
TouchUpOutside(this, pointCollection[i].Position);
}
}
}
}
I’ve
also used this approach to develop an multi-touch XAML game for flying an Bluetooth
BeeWi helicopter. I will also have a session on the 27th February at
Community Days here in Italy where I will present a session on developing a
game for Windows Phone and I will use this game as a starting point. This application has multi-touch buttons, slider and joystick control.
Also
have to thank the TTT (Train The Trainer) program which awarded me a beautiful
Sphero for my multi-touch controls.
As
always don’t hesitate to contact me if you have further questions.
NAMASTE
