如何在xamarin表单中启用放大和缩小内容页面？

Question

如何在xamarin表单中启用内容页面缩放？是否可以在整个内容页面上启用它？或者只能放大图像？

Answer 1

关于Xamarin.Forms的最新功能是ContentPage中的捏手势，这是官方页面：

https://developer.xamarin.com/guides/xamarin-forms/user-interface/gestures/pinch/

以及整个项目样本：

https://github.com/xamarin/xamarin-forms-samples/tree/master/WorkingWithGestures/PinchGesture

以下是您可以实现的目标示例：

Xamarin.Forms Pinch Example

Answer 2

尝试此类，此解决方案在缩放时不会滚动。 来源： Source Code

    public class PinchToZoomContainer : ContentView {
    double currentScale = 1;
    double startScale = 1;
    double xOffset = 0;
    double yOffset = 0;

    public PinchToZoomContainer ()
    {
        var pinchGesture = new PinchGestureRecognizer ();
        pinchGesture.PinchUpdated += OnPinchUpdated;
        GestureRecognizers.Add (pinchGesture);
    }

    void OnPinchUpdated (object sender, PinchGestureUpdatedEventArgs e)
    {
        if (e.Status == GestureStatus.Started) {
            // Store the current scale factor applied to the wrapped user interface element,
            // and zero the components for the center point of the translate transform.
            startScale = Content.Scale;
            Content.AnchorX = 0;
            Content.AnchorY = 0;
        }
        if (e.Status == GestureStatus.Running) {
            // Calculate the scale factor to be applied.
            currentScale += (e.Scale - 1) * startScale;
            currentScale = Math.Max (1, currentScale);

            // The ScaleOrigin is in relative coordinates to the wrapped user interface element,
            // so get the X pixel coordinate.
            double renderedX = Content.X + xOffset;
            double deltaX = renderedX / Width;
            double deltaWidth = Width / (Content.Width * startScale);
            double originX = (e.ScaleOrigin.X - deltaX) * deltaWidth;

            // The ScaleOrigin is in relative coordinates to the wrapped user interface element,
            // so get the Y pixel coordinate.
            double renderedY = Content.Y + yOffset;
            double deltaY = renderedY / Height;
            double deltaHeight = Height / (Content.Height * startScale);
            double originY = (e.ScaleOrigin.Y - deltaY) * deltaHeight;

            // Calculate the transformed element pixel coordinates.
            double targetX = xOffset - (originX * Content.Width) * (currentScale - startScale);
            double targetY = yOffset - (originY * Content.Height) * (currentScale - startScale);

            // Apply translation based on the change in origin.
            Content.TranslationX = targetX.Clamp (-Content.Width * (currentScale - 1), 0);
            Content.TranslationY = targetY.Clamp (-Content.Height * (currentScale - 1), 0);

            // Apply scale factor
            Content.Scale = currentScale;
        }
        if (e.Status == GestureStatus.Completed) {
            // Store the translation delta's of the wrapped user interface element.
            xOffset = Content.TranslationX;
            yOffset = Content.TranslationY;
        }
    }
}

Helper DoubleExtensions

    public static class DoubleExtensions
{
    public static double Clamp (this double self, double min, double max)
    {
        return Math.Min (max, Math.Max (self, min));
    }
}

Answer 3

您可以尝试在“内容”页面上使用“缩放Api”。这似乎对我的小测试应用程序有用。

public App ()
{
    // The root page of your application
    var scaleUp = new Button {
        Text = "Scale Up"
    };
    scaleUp.Clicked += (sender, e) => {
        this.MainPage.Scale += 1;
    };

    var scaleDown = new Button {
        Text = "Scale Down"
    };
    scaleDown.Clicked += (object sender, EventArgs e) => {
        this.MainPage.Scale -= 1;
    };

    MainPage = new ContentPage {
        Content = new StackLayout {
            VerticalOptions = LayoutOptions.Center,
            Children = {
                scaleUp,
                scaleDown

            }
        }
    };
}

Answer 4

您可以使用手势。 此处示例：http://arteksoftware.com/gesture-recognizers-with-xamarin-forms/