Linien dynamisch zur Laufzeit zeichnen

import android.app.Fragment;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;

/**
 * Created by phillipp on 03.01.2015.
 */
public class fragment1 extends Fragment{

    private int x ;
    private int y ;
    private Canvas mCanvas;
    Paint paint = new Paint();



    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);



    }

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

        View fraglayoutv = inflater.inflate(R.layout.frag1_layout, null);
        return fraglayoutv;
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
    }
    
    
    public void Eins(){

        mCanvas.drawLine(0,10,20,30,paint);
    }
    
    
    public void Zwei(){
        mCanvas.drawLine(5,15,30,80/2,paint);
    }
    
    

    public class  draw extends View {

        public draw(Context context) {
            super(context);
            context.getResources();
        }

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

            paint.setColor(Color.MAGENTA);
            x=getWidth()-1;
            y=getHeight()-1;
            mCanvas = canvas;
            Eins();
            Zwei();
        }
    }


}

public class MainActivity extends ActionBarActivity
        implements NavigationDrawerFragment.NavigationDrawerCallbacks {




    /**
     * Fragment managing the behaviors, interactions and presentation of the navigation drawer.
     */
    private NavigationDrawerFragment mNavigationDrawerFragment;
    public fragment1 frag1;
    public fragment2 frag2;
    public fragment3 frag3;
    public android.app.FragmentManager fragmanager ;
    public FragmentTransaction fragtrans;
    ImageView imV;



    /**
     * Used to store the last screen title. For use in {@link #restoreActionBar()}.
     */
    private CharSequence mTitle;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mNavigationDrawerFragment = (NavigationDrawerFragment)
                getSupportFragmentManager().findFragmentById(R.id.navigation_drawer);
        mTitle = getTitle();



        // Set up the drawer.
        mNavigationDrawerFragment.setUp(
                R.id.navigation_drawer,
                (DrawerLayout) findViewById(R.id.drawer_layout));

    }

    @Override
    public void onNavigationDrawerItemSelected(int position) {
        // update the main content by replacing fragments
        FragmentManager fragmentManager = getSupportFragmentManager();
        fragmentManager.beginTransaction()
                .replace(R.id.container, PlaceholderFragment.newInstance(position + 1))
                .commit();
        frag1 = (fragment1) android.app.Fragment.instantiate(this,fragment1.class.getName(),null );
        frag2 = (fragment2) android.app.Fragment.instantiate(this,fragment2.class.getName(),null );
        frag3 = (fragment3) android.app.Fragment.instantiate(this,fragment3.class.getName(),null );
        fragmanager = getFragmentManager();
        fragtrans = fragmanager.beginTransaction();
        fragtrans.add(R.id.container,frag1);
        fragtrans.commit();


    }

    public void onSectionAttached(int number) {
        switch (number) {
            case 1:

                mTitle = getString(R.string.title_section1);
                fragmanager = getFragmentManager();
                fragtrans = fragmanager.beginTransaction();
                fragtrans.replace(R.id.container, frag1);
                fragtrans.commit();
                
                
                // Hier müsste ja die draw klasse aufgerufen werden oder nicht ????? 



                break;
            case 2:
                mTitle = getString(R.string.title_section2);
                fragmanager = getFragmentManager();
                fragtrans = fragmanager.beginTransaction();
                fragtrans.replace(R.id.container, frag2);
                fragtrans.commit();

                break;
            case 3:
                mTitle = getString(R.string.title_section3);
                fragmanager = getFragmentManager();
                fragtrans = fragmanager.beginTransaction();
                fragtrans.replace(R.id.container, frag3);
                fragtrans.commit();
                break;
        }
    }

    public void restoreActionBar() {
        ActionBar actionBar = getSupportActionBar();
        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_STANDARD);
        actionBar.setDisplayShowTitleEnabled(true);
        actionBar.setTitle(mTitle);
    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        if (!mNavigationDrawerFragment.isDrawerOpen()) {
            // Only show items in the action bar relevant to this screen
            // if the drawer is not showing. Otherwise, let the drawer
            // decide what to show in the action bar.
            getMenuInflater().inflate(R.menu.main, menu);
            restoreActionBar();
            return true;
        }
        return super.onCreateOptionsMenu(menu);
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    /**
     * A placeholder fragment containing a simple view.
     */
    public static class PlaceholderFragment extends Fragment {
        /**
         * The fragment argument representing the section number for this
         * fragment.
         */
        private static final String ARG_SECTION_NUMBER = "section_number";

        /**
         * Returns a new instance of this fragment for the given section
         * number.
         */
        public static PlaceholderFragment newInstance(int sectionNumber) {
            PlaceholderFragment fragment = new PlaceholderFragment();
            Bundle args = new Bundle();
            args.putInt(ARG_SECTION_NUMBER, sectionNumber);
            fragment.setArguments(args);
            return fragment;
        }

        public PlaceholderFragment() {
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                                 Bundle savedInstanceState) {
            View rootView = inflater.inflate(R.layout.fragment_main, container, false);

            return rootView;
        }

        @Override
        public void onAttach(Activity activity) {
            super.onAttach(activity);
            ((MainActivity) activity).onSectionAttached(
                    getArguments().getInt(ARG_SECTION_NUMBER));
        }
    }

}