android - 我是否需要使用无效调用，如果需要，在哪里？

Question

我有一个显示 View 的 Activity ，在 View 中有一个正在绘制的 Canvas ，然后我有一个允许拖动/缩放 Canvas 的 ontouch 函数。但是，在调试时它似乎可以正常工作，只是 Canvas 没有移动。我认为我需要调用 invalidate，对吗？如果是这样，我应该在哪里调用它？

感谢您能给我的任何帮助。

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);

      // Handle 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);
   }
}

和 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);

}}

Answer 1

当你想重绘屏幕时调用invalidate。如果你想让它不断更新，你可以在 onDraw 阶段结束时调用它，它会一遍又一遍地绘制它。

如果你只需要在缩放后重绘屏幕，那么在缩放功能完成后重绘