android - Is it possible to display multi-color text with one call to Canvas.drawText()?

Question

I would like to use Canvas.drawText() to display multi-color text. More specifically, I want to highlight a substring of the text passed to the drawText() method.

The text is in the form of a SpannableString with 0 or more ForegroundColorSpan objects.

Looking at the Canvas code, it appears that a .toString() call on the passed CharSequence, means that this is not possible.

Is there an alternative way?

EDIT: The text may occasionally change (total changes, not incremental). Also, there are potentially multiple texts positioned in different unrelated locations in the custom view.

Answer 1

Yes it is possible by using one of the Layout classes. These are helper classes for drawing text to a canvas and they support Spannables. If your text doesn't change use a StaticLayout.

Example

Add this to your custom view class

private StaticLayout layout;

put this code into your onLayout or onSizeChanged

Spannable wordtoSpan = new SpannableString("I know just how to whisper, And I know just how to cry,I know just where to find the answers");  

wordtoSpan.setSpan(new ForegroundColorSpan(Color.BLUE), 15, 30, Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);

TextPaint paint = new TextPaint();
paint.setTextSize(20f);
paint.setColor(Color.RED);
layout = new StaticLayout(wordtoSpan, paint, getWidth(), Alignment.ALIGN_NORMAL, 1, 0, false);

Then in your drawing method simply call

layout.draw(canvas);

In case your text changes often you can use a DynamicLayout.

Editable.Factory fac = Editable.Factory.getInstance();
Editable edit = fac.newEditable(wordtoSpan);
DynamicLayout layout = new DynamicLayout(edit,paint,getWidth(),Alignment.ALIGN_CENTER,1,0,false);

change text by using the edit object

edit.append("hello");