Measuring text in WPF

问题:

Using WPF, what is the most efficient way to measure a large number of short strings? Specifically, I'd like to determine the display height of each string, given uniform formatting (same font, size, weight, etc.) and the maximum width the string may occupy?

回答1:

The most low-level technique (and therefore giving the most scope for creative optimisations) is to use GlyphRuns.

It's not very well documented but I wrote up a little example here:

http://smellegantcode.wordpress.com/2008/07/03/glyphrun-and-so-forth/

The example works out the length of the string as a necessary step before rendering it.

回答2:

It is very simple and done by FormattedText class! Try it.

回答3:

In WPF:

Remember to call Measure() on the TextBlock before reading the DesiredSize property.

If the TextBlock was created on-the-fly, and not yet shown, you have to call Measure() first, like so:

MyTextBlock.Measure(new Size(Double.PositiveInfinity, Double.PositiveInfinity));

return new Size(MyTextBlock.DesiredSize.Width, MyTextBlock.DesiredSize.Height);

In Silverlight:

No need to measure.

return new Size(TextBlock.ActualWidth, TextBlock.ActualHeight);

The complete code looks like this:

public Size MeasureString(string s) {

    if (string.IsNullOrEmpty(s)) {
        return new Size(0, 0);
    }

    var TextBlock = new TextBlock() {
        Text = s
    };

#if SILVERLIGHT
    return new Size(TextBlock.ActualWidth, TextBlock.ActualHeight);
#else
    TextBlock.Measure(new Size(Double.PositiveInfinity, Double.PositiveInfinity));

    return new Size(TextBlock.DesiredSize.Width, TextBlock.DesiredSize.Height);
#endif
}

回答4:

You can use the DesiredSize property on a rendered TextBox to get the height and width

using System.Windows.Threading;

...

Double TextWidth = 0;
Double TextHeight = 0;
...

MyTextBox.Text = "Words to measure size of";
this.Dispatcher.BeginInvoke(
    DispatcherPriority.Background,
    new DispatcherOperationCallback(delegate(Object state) {
        var size = MyTextBox.DesiredSize;
        this.TextWidth = size.Width;
        this.TextHeight = size.Height;
        return null; 
    }
) , null);

If you have a large number of strings it may be quicker to first pre-calualte the height and width of every indiviudal letter and symbol in a given font, and then do a calculation based on the string chars. This may not be 100% acurate due to kerning etc