Rickard Lindroth Rickard Lindroth - 5 months ago 23
Android Question

How to write centered multi-colored text to a canvas?

I am writing to a canvas from a thread.

public void draw(Canvas canvas) {
Paint p = new Paint();
p.setAntiAlias(true);
p.setTextSize(30);
p.setColor(Color.WHITE);
p.setTextAlign(Paint.Align.CENTER);

canvas.drawText("Centered", xCentre, yCentre, p);
}


My problem start when I have a multi colored
SpannableStringBuilder
which I want to write to the canvas, and I have no idea how to do this.
SpannableStringBuilder
has a
drawText()
method which I have been unable to use. Or is there some other method to write a string to a canvas where some of the letters have a different color?

Answer

I found the solution to this myself.

You can calculate the width that the string will have after being drawn on the canvas. Then you know where too continue to paint text to the canvas after having changed color.

package com.example;

import android.app.Activity;
import android.content.Context;
import android.graphics.*;
import android.os.Bundle;
import android.view.View;

public class MyActivity extends Activity {

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(new SampleView(this));
  }

  private static class SampleView extends View {
    public SampleView(Context context) {
      super(context);
    }

    @Override
    protected void onDraw(Canvas canvas) {
      canvas.drawColor(Color.WHITE);

      String blackText = "black";
      String redText = " red";

      Paint mPaint = new Paint();
      mPaint.setAntiAlias(true);
      mPaint.setTextSize(30);
      mPaint.setTypeface(Typeface.create(Typeface.SERIF,
          Typeface.ITALIC));

      float canvasWidth = canvas.getWidth();
      float blackTextWidth = mPaint.measureText(blackText);
      float sentenceWidth = mPaint.measureText(blackText + redText);
      float startPositionX = (canvasWidth - sentenceWidth) / 2;

      mPaint.setTextAlign(Paint.Align.LEFT);
      canvas.translate(0, 80);

      mPaint.setColor(Color.BLACK);
      canvas.drawText(blackText, startPositionX, 0, mPaint);
      mPaint.setColor(Color.RED);
      canvas.drawText(redText, startPositionX + blackTextWidth, 0,mPaint);

    }
  }
}