how to save signature in android?

Hi I have created a panel and signature can be drawn on the panel.When I click on the save button the signature has to be saved in a file.I have tried with the following coding but could not save the file.I am getting exception in logcat.

public class Signatures_saveActivity extends Activity {

    LinearLayout mContent;
    signature mSignature;
    Button mClear, mGetSign;
    public static String tempDir;
    public int count = 1;
    public String current = null;
    private Bitmap mBitmap;
    View mView;
    String ss;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        tempDir = Environment.getExternalStorageDirectory() + "/"
                + getResources().getString(R.string.external_dir) + "/";
        prepareDirectory();
        current = count + ".png";

        mContent = (LinearLayout) findViewById(R.id.linearLayout);
        mSignature = new signature(this, null);
        mSignature.setBackgroundColor(Color.BLUE);
        mContent.addView(mSignature, LayoutParams.FILL_PARENT,
                LayoutParams.FILL_PARENT);
        mClear = (Button) findViewById(R.id.clear);
        mGetSign = (Button) findViewById(R.id.getsign);
        mView = mContent;

        mClear.setOnClickListener(new OnClickListener() {
            public void onClick(View v) {
                Log.v("log_tag", "Panel Cleared");
                mSignature.clear();
            }
        });

        mGetSign.setOnClickListener(new OnClickListener() {
            public void onClick(View v) {
                Log.v("log_tag", "Panel Saved");
                mView.setDrawingCacheEnabled(true);
                mSignature.save(mView);

            }
        });

    }

    private boolean prepareDirectory() {
        try {
            if (makedirs()) {
                return true;
            } else {
                return false;
            }
        } catch (Exception e) {
 开发者_开发技巧           e.printStackTrace();
            Toast.makeText(
                    this,
                    "Could not initiate File System.. Is Sdcard mounted properly?",
                    1000).show();
            return false;
        }
    }

    private boolean makedirs() {
        File tempdir = new File(tempDir);
        if (!tempdir.exists())
            tempdir.mkdirs();

        if (tempdir.isDirectory()) {
            File[] files = tempdir.listFiles();
            for (File file : files) {
                if (!file.delete()) {
                    System.out.println("Failed to delete " + file);
                }
            }
        }
        return (tempdir.isDirectory());
    }

    public class signature extends View {
        private static final float STROKE_WIDTH = 5f;
        private static final float HALF_STROKE_WIDTH = STROKE_WIDTH / 2;
        private Paint paint = new Paint();
        private Path path = new Path();

        private float lastTouchX;
        private float lastTouchY;
        private final RectF dirtyRect = new RectF();

        public signature(Context context, AttributeSet attrs) {
            super(context, attrs);
            paint.setAntiAlias(true);
            paint.setColor(Color.YELLOW);
            paint.setStyle(Paint.Style.STROKE);
            paint.setStrokeJoin(Paint.Join.ROUND);
            paint.setStrokeWidth(STROKE_WIDTH);
        }

        public void save(View v) {
            Log.v("log_tag", "Width: " + v.getWidth());
            Log.v("log_tag", "Height: " + v.getHeight());

            if (mBitmap == null) {
                mBitmap = Bitmap.createBitmap(320, 480, Bitmap.Config.RGB_565);
            }
            Canvas canvas = new Canvas(mBitmap);
            String FtoSave = tempDir + current;
            File file = new File(FtoSave);
            try {
                FileOutputStream mFileOutStream = new FileOutputStream(file);
                v.draw(canvas);
                mBitmap.compress(Bitmap.CompressFormat.PNG, 90, mFileOutStream);

                // Bitmap bmp = intent.getExtras().get("data");
//              ByteArrayOutputStream stream = new ByteArrayOutputStream();
//              mBitmap.compress(Bitmap.CompressFormat.PNG, 100, stream);
//              byte[] val = stream.toByteArray();
//                String s = new String(val.toString());
//              
//               ss = Base64.encodeToString(val, Base64.DEFAULT);
//               System.out.println("String image data" + ss);

                mFileOutStream.flush();
                mFileOutStream.close();
                String url = Images.Media.insertImage(getContentResolver(),
                        mBitmap, "title", null);
                Log.v("log_tag", "url" + url);

            } catch (Exception e) {
                Log.v("log_tag", e.toString());
            }
        }

        public void clear() {
            path.reset();
            invalidate();
        }

        @Override
        protected void onDraw(Canvas canvas) {
            canvas.drawPath(path, paint);
        }

        @Override
        public boolean onTouchEvent(MotionEvent event) {
            float eventX = event.getX();
            float eventY = event.getY();

            switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                path.moveTo(eventX, eventY);
                lastTouchX = eventX;
                lastTouchY = eventY;
                return true;

            case MotionEvent.ACTION_MOVE:

            case MotionEvent.ACTION_UP:
                resetDirtyRect(eventX, eventY);
                int historySize = event.getHistorySize();
                for (int i = 0; i < historySize; i++) {
                    float historicalX = event.getHistoricalX(i);
                    float historicalY = event.getHistoricalY(i);
                    expandDirtyRect(historicalX, historicalY);
                    path.lineTo(historicalX, historicalY);
                }
                path.lineTo(eventX, eventY);
                break;

            default:
                debug("Ignored touch event: " + event.toString());
                return false;
            }

            invalidate((int) (dirtyRect.left - HALF_STROKE_WIDTH),
                    (int) (dirtyRect.top - HALF_STROKE_WIDTH),
                    (int) (dirtyRect.right + HALF_STROKE_WIDTH),
                    (int) (dirtyRect.bottom + HALF_STROKE_WIDTH));

            lastTouchX = eventX;
            lastTouchY = eventY;

            return true;
        }

        private void debug(String string) {
        }

        private void expandDirtyRect(float historicalX, float historicalY) {
            if (historicalX < dirtyRect.left) {
                dirtyRect.left = historicalX;
            } else if (historicalX > dirtyRect.right) {
                dirtyRect.right = historicalX;
            }

            if (historicalY < dirtyRect.top) {
                dirtyRect.top = historicalY;
            } else if (historicalY > dirtyRect.bottom) {
                dirtyRect.bottom = historicalY;
            }
        }

        private void resetDirtyRect(float eventX, float eventY) {
            dirtyRect.left = Math.min(lastTouchX, eventX);
            dirtyRect.right = Math.max(lastTouchX, eventX);
            dirtyRect.top = Math.min(lastTouchY, eventY);
            dirtyRect.bottom = Math.max(lastTouchY, eventY);
        }
    }
}

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Make sure you have write permission to external storage set up in your manifest: http://developer.android.com/reference/android/Manifest.permission.html#WRITE_EXTERNAL_STORAGE