你如何檢測兩個手指繪製兩個獨立的圓？

Question

我試圖創建下面的代碼來檢測兩個手指，並讓它跟蹤不同彩色圓圈表示的運動。但是，我不確定如何有多個圓圈工作。

import android.content.Context; 
import android.graphics.Canvas; 
import android.graphics.Color; 
import android.graphics.Paint; 
import android.support.v4.view.MotionEventCompat; 
import android.util.AttributeSet; 
import android.view.MotionEvent; 
import android.view.View; 

public class MyExtendedView extends View { 

    static int touchDoneCounter = 2; 

    static String DEBUG_TAG = "CUSTOM_VIEW_INFO"; 

    float x=0, y=0; 

    // The constructor is called first 
    public MyExtendedView(Context ctx, AttributeSet attrs) { 

     super(ctx, attrs); 

     // Set the background color to black 
     this.setBackgroundColor(Color.BLACK); 
    } 

    // This method is called before the view is drawn first, on screen rotation and when forceredraw is called 
    protected void onDraw(Canvas canvas) { 

     super.onDraw(canvas); 

     Paint p = new Paint(); 
     p.setColor(Color.YELLOW); 

     Paint g = new Paint(); 
     g.setColor(Color.GREEN); 


     // draw the circle where the touch occurs. At start, x and y are zero so the circle is drawn on top right 
     canvas.drawCircle(x, y, 75f, p); 



    } 



    // This is called when a touch is registered 
    @Override 
    public boolean onTouchEvent(MotionEvent event) { 


     int action = MotionEventCompat.getActionMasked(event); 

     // logging the kind of event we got 
     switch (action) { 
      case MotionEvent.ACTION_DOWN: 
      case MotionEvent.ACTION_POINTER_DOWN: { 
       break; 
      } 

      case MotionEvent.ACTION_MOVE: { // a pointer was moved 
       break; 
      } 

      case MotionEvent.ACTION_UP: 
      case MotionEvent.ACTION_POINTER_UP: 
      case MotionEvent.ACTION_CANCEL: { 
       break; 
      } 
     } 
     //1.5 at this point we re-draw the circle where the touch occurred 
     redrawViewWithCircle(event); 

     return true; 
    } 


    public void redrawViewWithCircle(MotionEvent event) { 

     // Get index 
     int index = MotionEventCompat.getActionIndex(event); 

     // Get coordinates for circle center. Set the instance variables. 
     this.x = (int)MotionEventCompat.getX(event, index); 
     this.y = (int)MotionEventCompat.getY(event, index); 

     // Force the view to redraw. 
     this.postInvalidate(); 

    } 

} 

我想我需要有一個指數和ID，但我不能確定這裏應該放置的位置。我在正確的軌道上嗎？

Answer 1

你在正確的軌道上。觸摸的每個手指都會有一個單獨的ID和索引。索引爲0 ... n（其中n是現在向下的手指數），ID可以更高並且有間隙（如果手指擡起）。對於你的應用，通過event.getX（index）和event.getY（index）跟蹤所有的x和y位置並將它們添加到Points列表中。然後，當您繪製時，在列表中的每個點繪製一個圓圈。爲了簡單起見，您可以簡單地清除並重建每個觸摸的列表，因爲我不能100％確定最終會產生什麼效果。