Adding an instance of my created class to xml file

i have a DrawingView class, that class creates an drawing view for. Code of that class you can see below. But the problem occurs when i want to create an instance of that class in xml file. What im doing wrong?

code of xml :

 <com.example.drawingapp.DrawingView
        android:id="@+id/drawing"
        android:layout_width="fill_parent"
        android:layout_height="0dp"
        android:layout_marginBottom="3dp"
        android:layout_marginLeft="5dp"
        android:layout_marginRight="5dp"
        android:layout_marginTop="3dp"
        android:layout_weight="1"
        android:background="#FFFFFFFF" />

Code of DrawingView class :

package com.example.drawingapp;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import android.widget.ImageButton;
import android.widget.LinearLayout;
import android.graphics.PorterDuff;
import android.graphics.PorterDuffXfermode;
import android.util.TypedValue;

public class DrawingView extends View {
    // drawing path
    private Path drawPath;
    // drawing and canvas paint
    private Paint drawPaint, canvasPaint;
    // initial color
    private int paintColor = 0xFF660000;
    // canvas
    private Canvas drawCanvas;
    // canvas bitmap
    private Bitmap canvasBitmap;
    private ImageButton currPaint;
    private DrawingView drawView;
    private boolean erase = false;

    private float brushSize, lastBrushSize;

    public DrawingView(Context context, AttributeSet attrs) {
        super(context, attrs);
        setupDrawing();
        drawView = (DrawingView) findViewById(R.id.drawing);
        LinearLayout paintLayout = (LinearLayout) findViewById(R.id.paint_colors);
        currPaint = (ImageButton) paintLayout.getChildAt(0);
        currPaint.setImageDrawable(getResources().getDrawable(
                R.drawable.paint_pressed));

    }

    private void setupDrawing() {
        // get drawing area setup for interacion
        drawPath = new Path();
        drawPaint = new Paint();

        drawPaint.setColor(paintColor);
        drawPaint.setAntiAlias(true);
        drawPaint.setStrokeWidth(20);
        drawPaint.setStyle(Paint.Style.STROKE);
        drawPaint.setStrokeJoin(Paint.Join.ROUND);
        drawPaint.setStrokeCap(Paint.Cap.ROUND);
        canvasPaint = new Paint(Paint.DITHER_FLAG);
        brushSize = getResources().getInteger(R.integer.medium_size);
        lastBrushSize = brushSize;
        drawPaint.setStrokeWidth(brushSize);
    }

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        // TODO Auto-generated method stub
        super.onSizeChanged(w, h, oldw, oldh);
        canvasBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
        drawCanvas = new Canvas(canvasBitmap);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        // TODO Auto-generated method stub
        canvas.drawBitmap(canvasBitmap, 0, 0, canvasPaint);
        canvas.drawPath(drawPath, drawPaint);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        // TODO Auto-generated method stub
        float touchX = event.getX();
        float touchY = event.getY();
        switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN:
            drawPath.moveTo(touchX, touchY);
            break;
        case MotionEvent.ACTION_MOVE:
            drawPath.lineTo(touchX, touchY);
            break;
        case MotionEvent.ACTION_UP:
            drawCanvas.drawPath(drawPath, drawPaint);
            drawPath.reset();
            break;
        default:
            return false;
        }
        invalidate();
        return true;
    }

    public void paintClicked(View view) {
        if (view != currPaint) {
            // update color
            drawView.setErase(false);
            drawView.setBrushSize(drawView.getLastBrushSize());
            ImageButton imgView = (ImageButton) view;
            String color = view.getTag().toString();
            drawView.setColor(color);
            imgView.setImageDrawable(getResources().getDrawable(
                    R.drawable.paint_pressed));
            currPaint.setImageDrawable(getResources().getDrawable(
                    R.drawable.paint));
            currPaint = (ImageButton) view;
        }
    }

    public void setColor(String newColor) {
        // set color
        invalidate();
        paintColor = Color.parseColor(newColor);
        drawPaint.setColor(paintColor);

    }

    public void setBrushSize(float newSize) {
        // update size
        float pixelAmount = TypedValue.applyDimension(
                TypedValue.COMPLEX_UNIT_DIP, newSize, getResources()
                        .getDisplayMetrics());
        brushSize = pixelAmount;
        drawPaint.setStrokeWidth(brushSize);
    }

    public void setLastBrushSize(float lastSize) {
        lastBrushSize = lastSize;
    }

    public float getLastBrushSize() {
        return lastBrushSize;
    }

    public void setErase(boolean isErase) {
        // set erase true or false
        erase = isErase;
        if (erase)
            drawPaint
                    .setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
        else
            drawPaint.setXfermode(null);
    }

    public void startNew() {
        drawCanvas.drawColor(0, PorterDuff.Mode.CLEAR);
        invalidate();
    }
}

Logcat shows me the error:

10-16 11:57:56.171: E/AndroidRuntime(17594): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.drawingapp/com.example.drawingapp.MainActivity}: android.view.InflateException: Binary XML file line #44: Error inflating class com.example.drawingapp.DrawingView