implements detection of drag&drop replacements on MyCanvas

src/ui/view/MyCanvas.java

@@ -598,6 +598,47 @@ public class MyCanvas extends AbstractCanvas implements MouseListener,
 
 		if (dragged) {
 			try {
+				/** x of the dragged Object */
+				int x = tempCps.getPosition().x;
+				
+				/** y of the dragged Object */
+				int y = tempCps.getPosition().y;
+				
+				/** distance treshold for replacement */
+				int treshhold = controller.getScale()/4;
+				
+				//System.out.println("Dragged "+tempCps.toString()+" to x: "+tempCps.getPosition().x+" y: "+tempCps.getPosition().y);
+				
+				/** number of Objects that might be replaced (should be 1) */
+				int replaceCounter = 0;
+				
+				/** last object that could be replaced */
+				AbstractCpsObject toBeReplaced = null;
+				
+				/** for each cps on Canvas */
+				for (AbstractCpsObject cps : model.getObjectsOnCanvas()){
+					
+					/** same object -> ignore */
+					if(cps == tempCps)continue;
+					
+					/** x of object that might get replaced */
+					int c_x = cps.getPosition().x;
+					
+					/** y of object that might get replaced */
+					int c_y = cps.getPosition().y;
+					
+					/** if near enough */
+					if(Math.abs(x-c_x)<treshhold && Math.abs(y-c_y)<treshhold){
+						replaceCounter++;
+						toBeReplaced = cps;
+					}
+				}
+				/** if replacement of exactly one object possible */
+				if(replaceCounter == 1 && toBeReplaced != null){
+					System.out.println(toBeReplaced.getName() + " should be replaced by " + tempCps.getName());
+					//TODO: replace
+				}
+				
 				controller.autoSave();
 			} catch (IOException ex) {
 				System.err.println("AutoSave error by dragging");