How to draw a stretched string with Canvas.drawText in Android

Question

I want to draw a SpannedStringbefore Canvas.

SpannableString spannableString = new SpannableString("Hello World!");
ForegroundColorSpan foregroundSpan = new ForegroundColorSpan(Color.RED);
BackgroundColorSpan backgroundSpan = new BackgroundColorSpan(Color.YELLOW);
spannableString.setSpan(foregroundSpan, 1, 8, Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
spannableString.setSpan(backgroundSpan, 3, spannableString.length() - 1, Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
textView.setText(spannableString);

The above example was compiled using TextView, which in turn uses Layoutto draw text with spaces. I know that using Layoutis the recommended way to draw text on canvas. However, I am making my own text layout from scratch, so I need to implement this myself.

Doing something like this does not work

canvas.drawText(spannableString, 0, spannableString.length(), 0, 0, mTextPaint);

because it drawTextreceives text only from spannableString, not from spans. Drawing colors are processed separately TextPaint.

canvas.drawText ( drawTextRun) ( , )?

• SpannedString SpannableString Android.
• Canvas.drawText()?

, , . , , . ( , , , .)

, :

• drawTextRun, (examples) ( : API 23)
• getRunAdvance, , ( : , API 23, measureText)
• , , ( drawRect , , drawPath? . , .)
• TextView, StaticLayout TextLine

Answer 1

, , , , StaticLayout . . .

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BackgroundColorSpan ForegroundColorSpan.

// set up the spanned string
SpannableString spannableString = new SpannableString("Hello World!");
ForegroundColorSpan foregroundSpan = new ForegroundColorSpan(Color.RED);
BackgroundColorSpan backgroundSpan = new BackgroundColorSpan(Color.YELLOW);
spannableString.setSpan(foregroundSpan, 1, 8, Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
spannableString.setSpan(backgroundSpan, 3, spannableString.length() - 1, Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);

// draw each span one at a time
int next;
float xStart = 0;
float xEnd;
for (int i = 0; i < spannableString.length(); i = next) {

    // find the next span transition
    next = spannableString.nextSpanTransition(i, spannableString.length(), CharacterStyle.class);

    // measure the length of the span
    xEnd = xStart + mTextPaint.measureText(spannableString, i, next);

    // draw the highlight (background color) first
    BackgroundColorSpan[] bgSpans = spannableString.getSpans(i, next, BackgroundColorSpan.class);
    if (bgSpans.length > 0) {
        mHighlightPaint.setColor(bgSpans[0].getBackgroundColor());
        canvas.drawRect(xStart, mTextPaint.getFontMetrics().top, xEnd, mTextPaint.getFontMetrics().bottom, mHighlightPaint);
    }

    // draw the text with an optional foreground color
    ForegroundColorSpan[] fgSpans = spannableString.getSpans(i, next, ForegroundColorSpan.class);
    if (fgSpans.length > 0) {
        int saveColor = mTextPaint.getColor();
        mTextPaint.setColor(fgSpans[0].getForegroundColor());
        canvas.drawText(spannableString, i, next, xStart, 0, mTextPaint);
        mTextPaint.setColor(saveColor);
    } else {
        canvas.drawText(spannableString, i, next, xStart, 0, mTextPaint);
    }

    xStart = xEnd;
}

. TextView ( StaticLayout).