Wrapping long text on an Android Canvas

I have a custom control that is doing a lot of 2D drawing straight to the canvas.

Some of this drawing is text, so I am using the Canvas.drawText() method.

I want to draw the text within some bounds - a top-left, certain maximum width, and a maximum number of lines. After drawing the text, I want to know how many lines it took.

Is there a built-in function to draw text within bounds doing the splitting sensibly?

If n开发者_StackOverflow中文版ot, is there a standard recipe for doing so?

You can use the android.text.StaticLayout class for this; simply create a StaticLayout for the desired text, alignment, width, etc. and call its draw(Canvas) method to draw to the canvas.

You can use Paint.getTextBounds() to measure the size of the entire string or Paint.getTextWidths() to get the width of each character. Then split the string appropriately before drawing it.

I had the same problem. One of my first solution is following.

/**
     * This function draws the text on the canvas based on the x-, y-position.
     * If it has to break it into lines it will do it based on the max width
     * provided.
     * 
     * @author Alessandro Giusa
     * @version 0.1, 14.08.2015
     * @param canvas
     *            canvas to draw on
     * @param paint
     *            paint object
     * @param x
     *            x position to draw on canvas
     * @param y
     *            start y-position to draw the text.
     * @param maxWidth
     *            maximal width for break line calculation
     * @param text
     *            text to draw
     */
public static void drawTextAndBreakLine(final Canvas canvas, final Paint paint,
        final float x, final float y, final float maxWidth, final String text) {
    String textToDisplay = text;
    String tempText = "";
    char[] chars;
    float textHeight = paint.descent() - paint.ascent();
    float lastY = y;
    int nextPos = 0;
    int lengthBeforeBreak = textToDisplay.length();
    do {
        lengthBeforeBreak = textToDisplay.length();
        chars = textToDisplay.toCharArray();
        nextPos = paint.breakText(chars, 0, chars.length, maxWidth, null);
        tempText = textToDisplay.substring(0, nextPos);
        textToDisplay = textToDisplay.substring(nextPos, textToDisplay.length());
        canvas.drawText(tempText, x, lastY, paint);
        lastY += textHeight;
    } while(nextPos < lengthBeforeBreak);
}

What is missing:

• No intelligent break-line mechanism, since it breaks based on the maxWidth

How to call?

    paint.setTextSize(40);
    paint.setColor(Color.WHITE);
    paint.setSubpixelText(true);
    float textHeight = paint.descent() - paint.ascent();
    CanvasUtils.drawTextAndBreakLine(canvas, paint, this.left,
            textHeight, this.displayWidth, this.text);

I have a static class called CanvasUtils where I encapsulate stuff like this. Basically I draw the text within a rectangle. This is the reason textHeight is the height of the text. But you can pass what you want to the function.

Good programming!