MonospaceSpan detects the widest char of given text and draws others with the same width

MonospaceSpan.java

import android.graphics.Canvas;
import android.graphics.Paint;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.text.style.ReplacementSpan;

public class MonospaceSpan extends ReplacementSpan {
    private boolean ignoreFullText;

    public void setIgnoreFullText(boolean ignoreFullText) {
        this.ignoreFullText = ignoreFullText;
    }

    private int getMaxCharWidth(@NonNull Paint paint, @NonNull CharSequence text, int start, int end, float[] widths) {
        if (widths == null) {
            widths = new float[end - start];
        }

        paint.getTextWidths(text, start, end, widths);

        float max = 0;

        for (float w : widths) {
            if (max < w) {
                max = w;
            }
        }

        return Math.round(max);
    }

    @Override
    public int getSize(@NonNull Paint paint, @NonNull CharSequence text, int start, int end, @Nullable Paint.FontMetricsInt fm) {
        if (fm != null) {
            paint.getFontMetricsInt(fm);
        }

        int count = end - start;

        if (text.charAt(start) == '\n') {
            count -= 1;
        }

        if (text.charAt(end - 1) == '\n') {
            count -= 1;
        }

        if (count < 0) {
            count = 0;
        }

        if (ignoreFullText) {
            return getMaxCharWidth(paint, text, start, end, null) * count;
        } else {
            return getMaxCharWidth(paint, text, 0, text.length(), null) * count;
        }
    }

    @Override
    public void draw(@NonNull Canvas canvas, @NonNull CharSequence text, int start, int end, float x, int top, int y, int bottom, @NonNull Paint paint) {
        float[] widths = new float[end - start];
        int max = getMaxCharWidth(paint, text, start, end, widths);

        if (!ignoreFullText) {
            max = getMaxCharWidth(paint, text, 0, text.length(), null);
        }

        for (int i = 0, n = end - start; i < n; ++i) {
            float p = (max - widths[i]) / 2;
            canvas.drawText(text, start + i, start + i + 1, x + max * i + p, y, paint);
        }
    }
}

Example

MainActivity.java

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.text.SpannableString;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        String text = "Lorem ipsum\ndolor sit amet\n0123456789";
        SpannableString textMono = new SpannableString(text);
        textMono.setSpan(new MonospaceSpan(), 0, textMono.length(), 0);

        TextView textView1 = findViewById(android.R.id.text1);
        TextView textView2 = findViewById(android.R.id.text2);

        textView1.setText(text);
        textView2.setText(textMono);
    }
}

res/layout/activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="center_horizontal"
    android:orientation="vertical"
    android:padding="16dp">

    <TextView
        android:id="@android:id/text1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="4dp"
        android:background="#fa0"
        android:fontFamily="@font/fredoka_one" />

    <TextView
        android:id="@android:id/text2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="4dp"
        android:background="#0af"
        android:fontFamily="@font/fredoka_one" />
</LinearLayout>

WARNING: This class breaks when handling CharSequences which include unicode Emojis, because those are represented using TWO CharSequence elements together. Displaying them one by one breaks the display (so instead of the emoji, you'll get two question marks).

To display the emoji correctly, line 70 needs to be "canvas.drawText(text, start + i, start + i + 2, x + max * i + p, y, paint);", but, only where it's needed. I don't have the solution, but I wanted to report this bug :')