Do I need to use an invalidate call and if so where?

I have an activity which shows a view, within the view there is a canvas which is draw, then I have an ontouch function which should allow the canvas to be dragged/zoomed. However when debugging it appears to work properly except there is no movement of the canvas. I think that I need to call invalidate, is this right? if so where should I call it?

Thanks for any help you can give me.

The Touch.java

package org.example.touch;

import android.app.Activity;
import android.content.Context;
import android.graphics.Matrix;
import android.graphics.PointF;
import android.os.Bundle;
import android.util.FloatMath;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnTouchListener;
import android.widget.ImageView;

public class Touch extends Activity implements OnTouchListener {
   private static final String TAG = "Touch";
   // These matrices will be used to move and zoom image
   Matrix matrix = new Matrix();
   Matrix savedMatrix = new Matrix();

   // We can be in one of these 3 states
   static final int NONE = 0;
   static final int DRAG = 1;
   static final int ZOOM = 2;
   int mode = NONE;

   // Remember some things for zooming
   PointF start = new PointF();
   PointF mid = new PointF();
   float oldDist = 1f;

   @Override
   public void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.main);
      GridView view = new GridView(this);
      setContentView(view);
      // ImageView view = (ImageView) findViewById(R.id.imageView);
      view.setOnTouchListener(this);

      // ...
      // Work around a Cupcake bug
      matrix.setTranslate(1f, 1f);
      view.setImageMatrix(matrix);

   }

   @Override
   public boolean onTouch(View v, MotionEvent rawEvent) {
      WrapMotionEvent event = WrapMotionEvent.wrap(rawEvent);
      // ...
      GridView view = (GridView) v;

      // Dump touch event to log
      dumpEvent(event);

      // Handl开发者_运维百科e touch events here...
      switch (event.getAction() & MotionEvent.ACTION_MASK) {
      case MotionEvent.ACTION_DOWN:
         savedMatrix.set(matrix);
         start.set(event.getX(), event.getY());
         Log.d(TAG, "mode=DRAG");
         mode = DRAG;
         break;
      case MotionEvent.ACTION_POINTER_DOWN:
         oldDist = spacing(event);
         Log.d(TAG, "oldDist=" + oldDist);
         if (oldDist > 10f) {
            savedMatrix.set(matrix);
            midPoint(mid, event);
            mode = ZOOM;
            Log.d(TAG, "mode=ZOOM");
         }
         break;
      case MotionEvent.ACTION_UP:
      case MotionEvent.ACTION_POINTER_UP:
         mode = NONE;
         Log.d(TAG, "mode=NONE");
         break;
      case MotionEvent.ACTION_MOVE:
         if (mode == DRAG) {

            matrix.set(savedMatrix);
            matrix.postTranslate(event.getX() - start.x,
                  event.getY() - start.y);
         }
         else if (mode == ZOOM) {
            float newDist = spacing(event);
            Log.d(TAG, "newDist=" + newDist);
            if (newDist > 10f) {
               matrix.set(savedMatrix);
               float scale = newDist / oldDist;
               matrix.postScale(scale, scale, mid.x, mid.y);
            }
         }
         break;
      }

      view.setImageMatrix(matrix);
      return true; // indicate event was handled
   }

   /** Show an event in the LogCat view, for debugging */
   private void dumpEvent(WrapMotionEvent event) {
      // ...
      String names[] = { "DOWN", "UP", "MOVE", "CANCEL", "OUTSIDE",
            "POINTER_DOWN", "POINTER_UP", "7?", "8?", "9?" };
      StringBuilder sb = new StringBuilder();
      int action = event.getAction();
      int actionCode = action & MotionEvent.ACTION_MASK;
      sb.append("event ACTION_").append(names[actionCode]);
      if (actionCode == MotionEvent.ACTION_POINTER_DOWN
            || actionCode == MotionEvent.ACTION_POINTER_UP) {
         sb.append("(pid ").append(
               action >> MotionEvent.ACTION_POINTER_ID_SHIFT);
         sb.append(")");
      }
      sb.append("[");
      for (int i = 0; i < event.getPointerCount(); i++) {
         sb.append("#").append(i);
         sb.append("(pid ").append(event.getPointerId(i));
         sb.append(")=").append((int) event.getX(i));
         sb.append(",").append((int) event.getY(i));
         if (i + 1 < event.getPointerCount())
            sb.append(";");
      }
      sb.append("]");
      Log.d(TAG, sb.toString());
   }

   /** Determine the space between the first two fingers */
   private float spacing(WrapMotionEvent event) {
      // ...
      float x = event.getX(0) - event.getX(1);
      float y = event.getY(0) - event.getY(1);
      return FloatMath.sqrt(x * x + y * y);
   }

   /** Calculate the mid point of the first two fingers */
   private void midPoint(PointF point, WrapMotionEvent event) {
      // ...
      float x = event.getX(0) + event.getX(1);
      float y = event.getY(0) + event.getY(1);
      point.set(x / 2, y / 2);
   }
}

and the view, GridView.java

package org.example.touch;

import android.app.Activity;
import android.os.Bundle;

import android.view.View;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Paint.Style;
import android.view.Display;
import android.graphics.Path;
import android.graphics.Bitmap;
import android.graphics.Matrix;
import android.graphics.Bitmap.Config;
import android.widget.ImageView;


public class GridView extends ImageView {

    private int canvasWidth;
    private int canvasHeight;

    // private Config config;
    // private Bitmap bitmap;
    // private Canvas canvas;

    public GridView(Context context) {
        super(context);




    // config = Bitmap.Config.ARGB_8888;
    // bitmap = Bitmap.createBitmap(canvasWidth, canvasHeight, config);
    // canvas = new Canvas(bitmap);

    }


public void onDraw(Canvas canvas){
    super.onDraw(canvas);

    canvasWidth = canvas.getWidth();
    canvasHeight = canvas.getHeight();

    Paint paint = new Paint();
    paint.setStyle(Paint.Style.FILL);

    paint.setColor(Color.WHITE);
    canvas.drawPaint(paint);


    canvas.drawRect(0, 0, (float)canvasWidth, (float)canvasHeight, paint);

    int Grid_size = canvasWidth / 32;


    paint.setStyle(Style.STROKE);
        paint.setColor(Color.RED);
        for (int i = 1; i < 100; i++) {                  
                canvas.drawLine((Grid_size*i), 10, (Grid_size*i), 10+(Grid_size*10), paint);              
               }                  
        paint.setColor(Color.RED);
            for (int i = 1; i < 12; i++) {                                  
                    canvas.drawLine(10, (Grid_size*i), (Grid_size*99), (Grid_size*i), paint); 
            }
            final int FS= 500;                  //Sampling Frequency
            final int WIN=FS*20; 

            //create a test sine wave
            short[]wave = new short[WIN];
            int frequency = 1;
            int amplitude = 40;
            for (int n=0; n<WIN; n++)
                wave[n] = (short) (60.0+amplitude*Math.sin(6.282*frequency*n/FS));

            //To display the waveform

            Path path2 = new Path();
            path2.moveTo(10, 60);

            for (float x2=1; x2<WIN; x2++)
                path2.lineTo(10+(3*x2/50), wave[(int) x2]);
            Paint paint3 = new Paint();
            paint3.setColor(Color.BLACK);
            paint3.setStyle(Style.STROKE);
            canvas.drawPath(path2, paint3);
}


//public void invalidate ();

public void setImageMatrix(Matrix matrix) {
    super.setImageMatrix(matrix);

}}

call invalidate for when you want the screen to be redrawn. If you want it to constantly update you can call it at the end of the onDraw stage and it will just draw it over and over.

If you only need the screen to be redrawn after you have zoomed then do it after the zoom function is finished