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TextBlocks

Use the TextBlock class to display text.

Setting the TextBlock.text property is the only way to show a text string. Because TextBlock inherits from GraphObject, some GraphObject properties will affect text. But there are additional text-only options regarding how that text is formatted and drawn. You can also pass the text string as the first argument to the constructor.

In some of these simple examples, the code programmatically creates a Part and adds it to the Diagram. Once you learn about models and data binding you will generally not create parts (nodes or links) programmatically.

Font and colors

The size and stylistic appearance of the text is specified by the TextBlock.font. The value may be any CSS font specifier string.

The text is drawn using the TextBlock.stroke brush. The value may be any CSS color string or a Brush. By default the stroke is "black".

You can also specify the brush to use as the background: GraphObject.background. This defaults to no brush at all, which results in a transparent background. The background is always rectangular.

Natural sizing of TextBlocks varies by browser

Because different browsers measure canvas text differently, TextBlocks are the only objects in GoJS that may have inconsistent natural sizes between browsers or different devices. For this reason, if you need objects to measure precisely and consistently across all browsers (such as for testing), TextBlocks without an explicit size (GraphObject.desiredSize or GraphObject.width and GraphObject.height) should not be used to dictate the size of any objects. For example, if you have a TextBlock with natural size inside an Panel.Auto Panel, set the size on that Auto Panel to fix the size of the area occupied by both the panel and its text.

Sizing and clipping

The natural size of a TextBlock is just big enough to render the text string with the given font. However the actual size of the TextBlock can be larger or smaller in either dimension. Larger dimensions result in areas with no text; smaller dimensions result in clipping.

To demonstrate this, the examples below start with a naturally sized TextBlock, followed by ones with decreasing explicit sizes.

Max lines and overflow

You can constrain the TextBlock's available size using GraphObject.desiredSize (width and height), but you can also limit the vertical height with TextBlock.maxLines, which will limit the number allowed. When there isn't enough space to display all text, you can decide how to use the remaining space with different values for TextBlock.overflow. There are additional options in the wrapping section below.

The example below starts with a naturally sized TextBlock, followed by one with a max of 2 lines using the default TextBlock.overflow value of OverflowClip, followed by one using the TextBlock.overflow value of OverflowEllipsis.

Wrapping

Text can also be automatically wrapped onto additional lines. In order for wrapping to happen, the TextBlock.wrap property must not be None, and there must be some constraint on the width to be narrower than it would naturally be.

In the following example, the first TextBlock gets its natural size, the second is limited to 80 wide but is not allowed to wrap, and the other examples are limited to the same width but are allowed to wrap.

Text alignment

The TextBlock.textAlign property specifies where to draw the characters horizontally within the size of the TextBlock. The value must be a CSS string.

This is different than the GraphObject.alignment property, which controls where to place the object within the area allocated by the parent Panel.

The TextBlock.verticalAlignment property controls the vertical alignment of the glyphs within the TextBlock. Neither TextBlock.textAlign nor TextBlock.verticalAlignment affect the sizing of the TextBlock.

TextAlign and Multiline

The TextBlock.textAlign property is useful even when the TextBlock has its natural size. This occurs when the text occupies multiple lines, whether by embedded newlines causing line breaks or by wrapping. You can control whether text starting with the first newline character is ignored by setting the TextBlock.isMultiline. By default multiline is enabled.

Editing

GoJS also supports the in-place editing of text by the user. You just need to set the TextBlock.editable property to true.

If you want to provide text validation of the user's input, you can set the TextBlock.textValidation property to a function. You can also provide a more customized or sophisticated text editor by setting the TextBlock.textEditor property. There is an example of text validation on the validation learn page.

When TextBlock.editable is true, it is commonplace to add a TwoWay Binding on the TextBlock.text property, so that new values are automatically saved into the model.

Indenting

Each line of text is normally trimmed of leading and trailing spaces before rendering. If you wish to indent a line of text by preserving leading spaces, start the line with the zero-width space character: \u200B. Wikipedia: Zero-width space

You can also use a \u200B character if you want to preserve spaces at the end of a line.

Flipping

You can flip text horizontally and vertically with the TextBlock.flip property:

Spacing above and spacing below

When using monospace or custom fonts you can specify a TextBlock.spacingAbove or TextBlock.spacingBelow to customize line spacing.

In the example below, the first TextBlock uses the monospace font and default line spacing. The second TextBlock makes use of TextBlock.spacingAbove and TextBlock.spacingBelow to improve readability.

Icon fonts

In some cases, you can show an icon that is provided by a font, instead of using a Picture or a Shape. First, make sure the font is loaded in the page before creating the diagram. Then you can show a string containing the Unicode code point for the desired icon.

Em sizing

Because GoJS uses an in-memory HTML Canvas to measure text, font sizes with em, rem, or % may not render as the correct size. We recommend you translate these font strings yourself to a pixel size. Typically this means multiplying em or rem by 16, or whatever the base pixel size of your document may be.