Main Actitivty

package pro.izcali.u4drawing;

import android.Manifest;
import android.content.pm.PackageManager;
import android.graphics.Bitmap;
import android.graphics.Color;
import android.os.Build;
import android.os.Bundle;
import android.os.Environment;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v4.app.ActivityCompat;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.util.Log;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.RelativeLayout;
import android.widget.Toast;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;

public class MainActivity extends AppCompatActivity {
    RelativeLayout parent;
    CanvasDrawing drawView;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        if (getPermissions()) {
            Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
            setSupportActionBar(toolbar);

            parent = (RelativeLayout) findViewById(R.id.canvasDrawing);
            drawView = new CanvasDrawing(this);

            parent.addView(drawView);


            FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
            fab.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View view) {
                    saveDraw();
                    Snackbar.make(view, "Guardado exitosamente", Snackbar.LENGTH_LONG)
                            .setAction("UNDO", null).show();
                }
            });

            FloatingActionButton fd = (FloatingActionButton) findViewById(R.id.fd);
            fd.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View view) {
                    drawView = new CanvasDrawing(view.getContext());

                    parent.addView(drawView);
                }
            });
        }else{
            finish();
        }
    }
    private boolean getPermissions() {
        Boolean granted = false;

        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
            if (checkSelfPermission(Manifest.permission.WRITE_EXTERNAL_STORAGE) == PackageManager.PERMISSION_GRANTED) {


                granted = true;
            }else{

                ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE}, 1);

                return false;
            }
        } else {
            granted = true;
        }

        return granted;
    }
    @Override
    public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
        if(grantResults[0]== PackageManager.PERMISSION_GRANTED){
          getPermissions();
        }
    }
    private void saveDraw() {
        parent.setDrawingCacheEnabled(true);
        Bitmap b = parent.getDrawingCache();

        FileOutputStream fos = null;
        try {
            fos = new FileOutputStream(getFileName());

        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }

        b.compress(Bitmap.CompressFormat.PNG, 95, fos);
    }
    public File getFileName() {

        return new File(Environment.getExternalStorageDirectory()+File.separator+"Download"+File.separator+"SignatureHDX.png");
    }
}