A custom Android View to capture a user's signature

SignatureView.java

/**
 * Copyright (C) 2016 by Vencil(vencsvencil@gmail.com)
 * Base canvas action is written by Matthew Silber (https://github.com/mattsilber/sigcap), Apache 2.0 licensed.
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.graphics.Path;
import android.util.AttributeSet;
import android.util.Base64;
import android.view.MotionEvent;
import android.view.View;

import java.io.ByteArrayOutputStream;
import java.util.ArrayList;
import java.util.List;

public class SignatureView extends View implements View.OnTouchListener {

    private List<List<Path>> signaturePaths = new ArrayList<>();
    private List<Path> activeSignaturePaths;
    private Paint signaturePaint;
    private Paint baselinePaint;

    private int baselinePaddingHorizontal = 0;
    private int baselinePaddingBottom = 0;
    private int baselineXMark = 0;
    private int baselineXMarkOffsetVertical = 0;

    private int[] lastTouchEvent;

    public SignatureView(Context context) {
        super(context);

        initDefaultValues();
    }

    public SignatureView(Context context, AttributeSet attrs) {
        super(context, attrs);

        initDefaultValues();
    }

    public SignatureView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);

        initDefaultValues();
    }

    protected void initDefaultValues() {
        setOnTouchListener(this);

        signaturePaint = new Paint();
        signaturePaint.setAntiAlias(true);
        signaturePaint.setColor(Color.BLACK);
        signaturePaint.setStyle(Paint.Style.FILL_AND_STROKE);
        signaturePaint.setStrokeWidth(15f);
        signaturePaint.setStrokeCap(Paint.Cap.ROUND);

        baselinePaint = new Paint();
        baselinePaint.setAntiAlias(true);
        baselinePaint.setColor(Color.BLACK);
        baselinePaint.setStyle(Paint.Style.FILL_AND_STROKE);
        baselinePaint.setStrokeWidth(1f);
        baselinePaint.setStrokeCap(Paint.Cap.ROUND);
    }


    @Override
    public boolean onTouch(View view, MotionEvent e) {
        int[] event = new int[]{(int) e.getX(), (int) e.getY()};

        if (e.getAction() == MotionEvent.ACTION_UP) {
            lastTouchEvent = null;

            signaturePaths.add(activeSignaturePaths);
            activeSignaturePaths = new ArrayList<>();
        } else if (e.getAction() == MotionEvent.ACTION_DOWN) {
            if (!(activeSignaturePaths == null || activeSignaturePaths.size() < 1))
                signaturePaths.add(activeSignaturePaths);

            activeSignaturePaths = new ArrayList<>();
        } else {
            Path path = new Path();
            path.moveTo(lastTouchEvent[0], lastTouchEvent[1]);
            path.lineTo(event[0], event[1]);

            activeSignaturePaths.add(path);
        }

        lastTouchEvent = event;

        postInvalidate();

        return true;
    }

    public void undoLastSignaturePath() {
        if (0 < signaturePaths.size()) {
            signaturePaths.remove(signaturePaths.size() - 1);

            postInvalidate();
        }
    }

    @Override
    public void onDraw(Canvas canvas) {
        super.onDraw(canvas);

        drawIndicators(canvas);
        drawSignaturePaths(canvas);
    }

    protected void drawIndicators(Canvas canvas) {
        canvas.drawLine(baselinePaddingHorizontal,
                canvas.getHeight() - baselinePaddingBottom,
                canvas.getWidth() - baselinePaddingHorizontal,
                canvas.getHeight() - baselinePaddingBottom,
                baselinePaint);

        drawXMark(canvas);
    }

    protected void drawXMark(Canvas canvas) {
        int radius = baselineXMark / 2;
        int cX = baselinePaddingHorizontal + radius;
        int cY = canvas.getHeight() - baselinePaddingBottom - radius - baselineXMarkOffsetVertical;

        canvas.save();
        canvas.rotate(-45, cX, cY);
        canvas.drawLine(cX - radius, cY, cX + radius, cY, baselinePaint);
        canvas.restore();

        canvas.save();
        canvas.rotate(45, cX, cY);
        canvas.drawLine(cX - radius, cY, cX + radius, cY, baselinePaint);
        canvas.restore();
    }

    protected void drawSignaturePaths(Canvas canvas) {
        for (List<Path> l : signaturePaths) {
            for (Path p : l) {
                canvas.drawPath(p, signaturePaint);
            }
        }

        if (activeSignaturePaths != null) {
            for (Path p : activeSignaturePaths) {
                canvas.drawPath(p, signaturePaint);
            }
        }
    }

    public String getContentDataURI() {
        setDrawingCacheEnabled(true);

        Bitmap bitmap = getDrawingCache();
        Bitmap cropBitmap = Bitmap.createBitmap(bitmap, 0, 0, bitmap.getWidth(), bitmap.getHeight() - 1);
        bitmap.recycle();

        Bitmap resizedBitmap = Bitmap.createScaledBitmap(cropBitmap, 300, 80, false);
        cropBitmap.recycle();

        ByteArrayOutputStream stream = new ByteArrayOutputStream();
        resizedBitmap.compress(Bitmap.CompressFormat.PNG, 100, stream);

        setDrawingCacheEnabled(false);

        return "data:image/png;base64," + Base64.encodeToString(baos.toByteArray(), Base64.NO_WRAP);
    }
}

SignatureViewDemoDialog.java

import android.app.Dialog;
import android.app.DialogFragment;
import android.app.Fragment;
import android.content.Context;
import android.content.DialogInterface;
import android.os.Bundle;
import android.support.v7.app.AlertDialog;
import android.view.ViewGroup;

public class SignatureViewDemoDialog extends DialogFragment {

    public static SignatureViewDemoDialog newInstance(Fragment caller) {

        SignatureViewDemoDialog demoDialog = new SignatureViewDemoDialog();
        demoDialog.setTargetFragment(caller, 0);

        return demoDialog;
    }

    @Override
    public Dialog onCreateDialog(Bundle savedInstanceState) {

        Context context = getActivity();
        final SignatureView signatureView = new SignatureView(context, null);

        AlertDialog.Builder builder = new AlertDialog.Builder(getActivity(), R.style.MaterialDialog);
        builder.setTitle("Signature demo")
                .setView(signatureView)
                .setPositiveButton("OK", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        String imageDataURI = signatureView.getContentDataURI();
                        // TODO data storage here
                    }
                });

        return builder.create();
    }

    @Override
    public void onCreate(Bundle icicle) {
        setCancelable(true);
        setRetainInstance(true);
        super.onCreate(icicle);
    }

    @Override
    public void onResume() {
        ViewGroup.LayoutParams params = getDialog().getWindow().getAttributes();
        params.height = 1000;
        getDialog().getWindow().setAttributes((android.view.WindowManager.LayoutParams) params);

        super.onResume();
    }

    @Override
    public void onDestroyView() {
        if (getDialog() != null && getRetainInstance()) {
            getDialog().setDismissMessage(null);
        }
        super.onDestroyView();
    }
}