代码滑动panorama-即程序中设置SelectedIndex

我们都知道panorama的SelectedIndex属性是只读的,所以通过修改它,在程序滑动panorama似乎不可能。那么是不是就没有办法了呢?
其实我们可以通过设置SelectedItemProperty这个依赖属性来改变SelectedItem的值。
设置方法如下:

pan.SetValue(Panorama.SelectedItemProperty, pan.Items[newIndex]);

虽然可以通过程序改变SelectedItem,但是panorama不会立即更新,我们只需要加一个小技巧,代码如下:

(pan.Items[curIndex] as PanoramaItem).Visibility = Visibility.Collapsed;
pan.SetValue(Panorama.SelectedItemProperty, pan.Items[(curIndex + 1) % pan.Items.Count]);
pan.Measure(new Size(double.PositiveInfinity, double.PositiveInfinity));
(pan.Items[curIndex] as PanoramaItem).Visibility = Visibility.Visible; 这样虽然实现了Item切换,却缺少动画效果,那么我们就需要找到相应的item控件,为其添加RenderTransform动画,即动画的target是RenderTransform。
具体实现如下:
private void slidePanorama(Panorama pan)
{
FrameworkElement panWrapper = VisualTreeHelper.GetChild(pan, 0) as FrameworkElement;
FrameworkElement panTitle = VisualTreeHelper.GetChild(panWrapper, 1) as FrameworkElement;
//Get the panorama layer to calculate all panorama items size
FrameworkElement panLayer = VisualTreeHelper.GetChild(panWrapper, 2) as FrameworkElement;
//Get the title presenter to calculate the title size
FrameworkElement panTitlePresenter = VisualTreeHelper.GetChild(VisualTreeHelper.GetChild(panTitle, 0) as FrameworkElement, 1) as FrameworkElement; //Current panorama item index
int curIndex = pan.SelectedIndex; //Get the next of next panorama item
FrameworkElement third = VisualTreeHelper.GetChild(pan.Items[(curIndex + 2) % pan.Items.Count] as PanoramaItem, 0) as FrameworkElement; //Be sure the RenderTransform is TranslateTransform
if (!(pan.RenderTransform is TranslateTransform)
|| !(panTitle.RenderTransform is TranslateTransform))
{
pan.RenderTransform = new TranslateTransform();
panTitle.RenderTransform = new TranslateTransform();
} //Increase width of panorama to let it render the next slide (if not, default panorama is 480px and the null area appear if we transform it)
pan.Width = 960; //Animate panorama control to the right
Storyboard sb = new Storyboard();
DoubleAnimation a = new DoubleAnimation();
a.From = 0;
a.To = -(pan.Items[curIndex] as PanoramaItem).ActualWidth; //Animate the x transform to a width of one item
a.Duration = new Duration(TimeSpan.FromMilliseconds(700));
a.EasingFunction = new CircleEase(); //This is default panorama easing effect
sb.Children.Add(a);
Storyboard.SetTarget(a, pan.RenderTransform);
Storyboard.SetTargetProperty(a, new PropertyPath(TranslateTransform.XProperty)); //Animate panorama title separately
DoubleAnimation aTitle = new DoubleAnimation();
aTitle.From = 0;
aTitle.To = (panLayer.ActualWidth - panTitlePresenter.ActualWidth) / (pan.Items.Count - 1) * 1.5; //Calculate where should the title animate to
aTitle.Duration = a.Duration;
aTitle.EasingFunction = a.EasingFunction; //This is default panorama easing effect
sb.Children.Add(aTitle);
Storyboard.SetTarget(aTitle, panTitle.RenderTransform);
Storyboard.SetTargetProperty(aTitle, new PropertyPath(TranslateTransform.XProperty)); //Start the effect
sb.Begin(); //After effect completed, we change the selected item
a.Completed += (obj, args) =>
{
//Reset panorama width
pan.Width = 480;
//Change the selected item
(pan.Items[curIndex] as PanoramaItem).Visibility = Visibility.Collapsed;
pan.SetValue(Panorama.SelectedItemProperty, pan.Items[(curIndex + 1) % pan.Items.Count]);
pan.Measure(new Size(double.PositiveInfinity, double.PositiveInfinity));
(pan.Items[curIndex] as PanoramaItem).Visibility = Visibility.Visible;
//Reset panorama render transform
(pan.RenderTransform as TranslateTransform).X = 0;
//Reset title render transform
(panTitle.RenderTransform as TranslateTransform).X = 0; //Because of the next of next item will be load after we change the selected index to next item
//I do not want it appear immediately without any effect, so I create a custom effect for it
if (!(third.RenderTransform is TranslateTransform))
{
third.RenderTransform = new TranslateTransform();
}
Storyboard sb2 = new Storyboard();
DoubleAnimation aThird = new DoubleAnimation() { From = 100, To = 0, Duration = new Duration(TimeSpan.FromMilliseconds(300)) }; sb2.Children.Add(aThird);
Storyboard.SetTarget(aThird, third.RenderTransform);
Storyboard.SetTargetProperty(aThird, new PropertyPath(TranslateTransform.XProperty));
sb2.Begin();
};
}
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