Get and Set a PointAnnotation Caption Position WPF

[AardvarkMan]

I'm creating a WPF application that displays a graph of data (several plots) and programmatically adds several annotations. The user is able to drag the annotation labels around (InteractionMode = AnnotationInteractionModes.DragLabel). I need to be able to save the new label position and load it back later.

I'm using the NationalInstruments.Controls.PointAnnotation object an a NationalInstruments.Controls.Graph.

I had thought it would be reflected in the LabelAlignment, but that doesn't appear to change from the value I set when I initially create the annotation.

Here is how I'm adding the annotations to the graph:

/// <summary>
        /// Add the annotations to the graph
        /// </summary>
        /// <param name="dataHandler"></param>
        /// <param name="StartDate"></param>
        /// <param name="EndDate"></param>
        private void DisplayAnnotations(DataHandler dataHandler, DateTime StartDate, DateTime EndDate)
        {
            PointAnnotation tmpAnnotation = new PointAnnotation();
            //Iterate through all the annotations in the source data set
            foreach (Post_Job_Charting.Annotation dataPointAnnotation in dataHandler.Annotations)
            {
                TimeSpan DateDiff = EndDate - StartDate;
                TimeSpan HalfWay = new TimeSpan(StartDate.AddSeconds(DateDiff.TotalSeconds / 2.0).Ticks);
 
                //Only add annotations that are in the visible data range
                if (dataPointAnnotation.Date >= StartDate && dataPointAnnotation.Date <= EndDate)
                {
                    tmpAnnotation = new PointAnnotation();
                    tmpAnnotation.HorizontalPosition = dataPointAnnotation.Date;
                    tmpAnnotation.VerticalPosition = dataPointAnnotation.Value;
                    tmpAnnotation.Label = dataPointAnnotation.Text;
 
                    if (dataPointAnnotation.Date.Ticks < HalfWay.Ticks) { tmpAnnotation.LabelAlignment = new AnnotationLabelAlignment(BoundsAlignment.None, 0, -25); }
                    else { tmpAnnotation.LabelAlignment = new AnnotationLabelAlignment(BoundsAlignment.None, -75, -25); }
                    tmpAnnotation.InteractionMode = AnnotationInteractionModes.DragLabel;
                    
                    //Show/Hide the annotation
                    if (dataPointAnnotation.Display) { tmpAnnotation.Visibility = System.Windows.Visibility.Visible; }
                    else { tmpAnnotation.Visibility = System.Windows.Visibility.Hidden; }
 
                    //Tag the annotation so I can find it later
                    tmpAnnotation.Tag = dataPointAnnotation.ID;
 
                    //Display annotation on the graph
                    niGraph.Children.Add(tmpAnnotation);
                }
            }
        }

Once I have the position of the label, I need to be able to reset the label to that position, but first things first, I need to get that position.

Any help you can offer would be greatly appreciated.

Best regards,

-Marcel

[phansen · Accepted solution]

There is no property on the point annotation that exposes the position of the label. I have created a task to look into adding this.

However, you can monitor the changes by using a custom BoundsAlignment implementation that records the new offset as it is updated:

    public sealed class RecordingBoundsAlignment : BoundsAlignment {
        public Vector LastOffset { get; private set; }

        public override Point AdjustPosition( AlignmentArgs args ) {
            LastOffset = new Vector( args.XOffset, args.YOffset );

            return None.AdjustPosition( args );
        }
    }

When you create the annotation, you would use an instance of the recording alignment, and when you wanted to save the position you would read the value from the recorder:

    tmpAnnotation.LabelAlignment = new AnnotationLabelAlignment(
        new RecordingBoundsAlignment( ),
        initialXOffset,
        initialYOffset );

    // ...

    var recorder = (RecordingBoundsAlignment)tmpAnnotation.LabelAlignment.Alignment;
    Save( recorder.LastOffset );

[AardvarkMan]

Fantastic solution! Thank you very much, I really appreciate your help.