package test.de;

import android.app.Activity;
import android.graphics.Color;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;

public class Unterschrift extends Activity {
    
    private static final int MENU_CLEAR = Menu.FIRST;
    private static final int MENU_SAVE = Menu.FIRST+1;
    private static final int MENU_LOAD = Menu.FIRST+2;
    
    private DrawView drawView = null;
    
    
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        
        drawView = new DrawView(this);
        drawView.setBackgroundColor(Color.WHITE);
        setContentView(drawView);
        drawView.requestFocus();
    }
    
    @Override public boolean onCreateOptionsMenu(Menu menu) {
        menu.add(0, MENU_CLEAR, 0, "Clear");
        menu.add(0, MENU_SAVE, 0, "Save");
        menu.add(0, MENU_LOAD, 0, "Load");
        return super.onCreateOptionsMenu(menu);
    }
    
    @Override public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case MENU_CLEAR:
                drawView.clearBitmap();
                return true;
            case MENU_SAVE:
                drawView.saveBitmap();
                return true;
            case MENU_LOAD:
                drawView.loadBitmap();
                return true;                
            default:
                return super.onOptionsItemSelected(item);
        }
    }
}

package test.de;

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

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Bitmap.CompressFormat;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.os.Environment;
import android.view.MotionEvent;
import android.view.View;


public class DrawView extends View {

    private Paint paint = new Paint();
    private float lastX, lastY;
    private boolean drawing = false;
    
    private Bitmap bitmap;
    private Canvas canvas;

    
    public DrawView(Context context) {
        super(context);
        setFocusable(true);
        paint.setAntiAlias(true);
        paint.setARGB(255, 255, 255, 255);        
    }
    
    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        bitmap = Bitmap.createBitmap(w, h, Bitmap.Config.RGB_565);
        canvas = new Canvas(bitmap);
        if (bitmap != null) {
            canvas.drawBitmap(bitmap, 0, 0, null);
        }        
        invalidate();
    }
    
    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        
        if (bitmap != null) {
            canvas.drawBitmap(bitmap, 0, 0, null);
        }        
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        if (event.getAction() == MotionEvent.ACTION_DOWN) {
            drawPoint(event.getX(), event.getY(), event.getPressure());
            return true;
        }
        else if (event.getAction() == MotionEvent.ACTION_UP) {
            drawing = false;
            return true;
        }
        else if (event.getAction() == MotionEvent.ACTION_MOVE) {
            drawing = true;
            drawPoint(event.getX(), event.getY(), event.getPressure());
            return true;            
        }
        
        return false;
    }
    
    private void drawPoint(float x, float y, float pressure) {
        if (bitmap != null) {            
            //int pressureLevel = (int)(pressure * 255);
            //paint.setARGB(pressureLevel, 255, 255, 255);
            paint.setARGB(255, 255, 255, 255);
            if (drawing) {
                canvas.drawLine(lastX, lastY, x, y, paint);
            }
            else {
                canvas.drawPoint(x, y, paint);
            }

            lastX = x;
            lastY = y;

            invalidate();
        }        
    }
    
    public void clearBitmap() {
        if (canvas != null) {
            paint.setARGB(0xff, 0, 0, 0);
            canvas.drawPaint(paint);
            invalidate();
        }
    }
    
    public void saveBitmap() {
        if (bitmap != null) {
            try {
                String path = Environment.getExternalStorageDirectory() + "/unterschrift/signatures";
                File dir = new File(path);
                if (!dir.exists() || !dir.isDirectory()) {
                    dir.mkdirs();
                }
                File file = new File(dir.getAbsolutePath() + "/signature.png");
                FileOutputStream fos;
                fos = new FileOutputStream(file);
                bitmap.compress(CompressFormat.PNG, 100, fos);
                fos.close();                
            } 
            catch (FileNotFoundException e) {
                e.printStackTrace();
            }
            catch (IOException io) {
                io.printStackTrace();
            }            
        }
    }
    
    public void loadBitmap() {
        String path = Environment.getExternalStorageDirectory() + "/unterschrift/signatures/signature.png";
        Bitmap bmp = BitmapFactory.decodeFile(path);
        if (bmp != null) {
            if (canvas != null) {
                canvas.drawBitmap(bmp, 0, 0, null);
            }
            invalidate();
        }
    }
}

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>