如何改变图像源，而在xamarin.forms ListView中点击？

问题描述：

我有一个ListView中，我有一个图像和viewcell，什么我的要求是要改变所选行的图像内的文字，我用它acheived，

I have a ListView in which I have a image and a Text inside a viewcell, What My requirement is to change the image on selected row, I acheived it by,

var listView = new MyQuestionView(listData);

        listView.ItemSelected += (sender, e) => {
            listView.ItemsSource = null;

            //Update the IconSource here in listData
            var s = e.SelectedItem as MenuItem;
            s.IconSource = "foo.png";

            listView.ItemsSource = listData; //Updated List
        };

不过，屏幕闪烁的第二个，同时更新这个样子。是否有更新行的元素之有道。

But, The screen flickers for a second while updating like this. Is there a proper way for updating a row's element.

这是code为我的列表视图：

public class MyQuestionView : ListView
{
    public MyQuestionView (ObservableCollection<MySelectedQuestions> Qdata)
    {
        ObservableCollection<MySelectedQuestions> data = Qdata;

        ItemsSource = data;
        HasUnevenRows = true;
        VerticalOptions = LayoutOptions.FillAndExpand;
        BackgroundColor = Color.Transparent;
        SeparatorVisibility = SeparatorVisibility.Default;
        SeparatorColor = Color.FromHex("#4Dffffff");
        VerticalOptions = LayoutOptions.FillAndExpand;
        HorizontalOptions = LayoutOptions.FillAndExpand;

        ItemTemplate = new DataTemplate (() => {

            // Create views with bindings for displaying each property.
            Label titleLabel = new Label ();
            titleLabel.FontSize = Device.GetNamedSize(NamedSize.Medium,typeof(Label));
            titleLabel.SetBinding (Label.TextProperty, "Text");
            Image image = new Image ();
            image.SetBinding(Image.SourceProperty, "IconSource");

            return new ViewCell {
                View = new StackLayout {
                    Padding = new Thickness (5),
                    Orientation = StackOrientation.Horizontal,
                    Children = {
                        image,
                        new StackLayout {
                            VerticalOptions = LayoutOptions.Center,
                            Spacing = 0,
                            Children = {
                                titleLabel
                            }
                        }
                    }
                }
            };
        });

    }
}

先谢谢了。

答

你可以使用触发器以避免闪烁做一些动画：

You could make some animations using Triggers to avoid flicker:

Image image = new Image ();
image.Triggers.Add(new Trigger(typeof(Image)) {
    Property = Image.SourceProperty,
    EnterActions = {
        new FadeTriggerAction() {
            StartsFrom = 1
        }
    },
    ExitActions = {
        new FadeTriggerAction() {
            StartsFrom = 0
        }
    }
});

FadeTriggerAction.cs：

public class FadeTriggerAction : TriggerAction<VisualElement>
{
    public FadeTriggerAction() {}

    public int StartsFrom { set; get; }

    protected override void Invoke (VisualElement visual)
    {
        visual.Animate("", new Animation( (d)=>{
            var val = StartsFrom == 0 ? d : 1-d;
            visual.Opacity = val;

        }),
            length:1000, // milliseconds
            easing: Easing.Linear);
    }
}

如何改变图像源，而在xamarin.forms ListView中点击？

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