Make the Pieces Snap into Place

app/src/main/java/dragosholban/com/androidpuzzlegame/MainActivity.java

@@ -15,7 +15,7 @@
 import static java.lang.Math.abs;
 
 public class MainActivity extends AppCompatActivity {
-    ArrayList<Bitmap> pieces;
+    ArrayList<PuzzlePiece> pieces;
 
     @Override
     protected void onCreate(Bundle savedInstanceState) {
@@ -32,23 +32,21 @@ protected void onCreate(Bundle savedInstanceState) {
             public void run() {
                 pieces = splitImage();
                 TouchListener touchListener = new TouchListener();
-                for(Bitmap piece : pieces) {
-                    ImageView iv = new ImageView(getApplicationContext());
-                    iv.setImageBitmap(piece);
-                    iv.setOnTouchListener(touchListener);
-                    layout.addView(iv);
+                for(PuzzlePiece piece : pieces) {
+                    piece.setOnTouchListener(touchListener);
+                    layout.addView(piece);
                 }
             }
         });
     }
 
-    private ArrayList<Bitmap> splitImage() {
+    private ArrayList<PuzzlePiece> splitImage() {
         int piecesNumber = 12;
         int rows = 4;
         int cols = 3;
 
         ImageView imageView = findViewById(R.id.imageView);
-        ArrayList<Bitmap> pieces = new ArrayList<>(piecesNumber);
+        ArrayList<PuzzlePiece> pieces = new ArrayList<>(piecesNumber);
 
         // Get the scaled bitmap of the source image
         BitmapDrawable drawable = (BitmapDrawable) imageView.getDrawable();
@@ -75,7 +73,14 @@ public void run() {
         for (int row = 0; row < rows; row++) {
             int xCoord = 0;
             for (int col = 0; col < cols; col++) {
-                pieces.add(Bitmap.createBitmap(croppedBitmap, xCoord, yCoord, pieceWidth, pieceHeight));
+                Bitmap pieceBitmap = Bitmap.createBitmap(croppedBitmap, xCoord, yCoord, pieceWidth, pieceHeight);
+                PuzzlePiece piece = new PuzzlePiece(getApplicationContext());
+                piece.setImageBitmap(pieceBitmap);
+                piece.xCoord = xCoord + imageView.getLeft();
+                piece.yCoord = yCoord + imageView.getTop();
+                piece.pieceWidth = pieceWidth;
+                piece.pieceHeight = pieceHeight;
+                pieces.add(piece);
                 xCoord += pieceWidth;
             }
             yCoord += pieceHeight;

app/src/main/java/dragosholban/com/androidpuzzlegame/PuzzlePiece.java

@@ -0,0 +1,15 @@
+package dragosholban.com.androidpuzzlegame;
+
+import android.content.Context;
+
+public class PuzzlePiece extends android.support.v7.widget.AppCompatImageView {
+    public int xCoord;
+    public int yCoord;
+    public int pieceWidth;
+    public int pieceHeight;
+    public boolean canMove = true;
+
+    public PuzzlePiece(Context context) {
+        super(context);
+    }
+}

app/src/main/java/dragosholban/com/androidpuzzlegame/TouchListener.java

@@ -2,8 +2,13 @@
 
 import android.view.MotionEvent;
 import android.view.View;
+import android.view.ViewGroup;
 import android.widget.RelativeLayout;
 
+import static java.lang.Math.pow;
+import static java.lang.Math.sqrt;
+import static java.lang.StrictMath.abs;
+
 public class TouchListener implements View.OnTouchListener {
     private float xDelta;
     private float yDelta;
@@ -12,19 +17,46 @@
     public boolean onTouch(View view, MotionEvent motionEvent) {
         float x = motionEvent.getRawX();
         float y = motionEvent.getRawY();
+        final double tolerance = sqrt(pow(view.getWidth(), 2) + pow(view.getHeight(), 2)) / 10;
+
+        PuzzlePiece piece = (PuzzlePiece) view;
+        if (!piece.canMove) {
+            return true;
+        }
+
         RelativeLayout.LayoutParams lParams = (RelativeLayout.LayoutParams) view.getLayoutParams();
         switch (motionEvent.getAction() & MotionEvent.ACTION_MASK) {
             case MotionEvent.ACTION_DOWN:
                 xDelta = x - lParams.leftMargin;
                 yDelta = y - lParams.topMargin;
+                piece.bringToFront();
                 break;
             case MotionEvent.ACTION_MOVE:
                 lParams.leftMargin = (int) (x - xDelta);
                 lParams.topMargin = (int) (y - yDelta);
                 view.setLayoutParams(lParams);
                 break;
+            case MotionEvent.ACTION_UP:
+                int xDiff = abs(piece.xCoord - lParams.leftMargin);
+                int yDiff = abs(piece.yCoord - lParams.topMargin);
+                if (xDiff <= tolerance && yDiff <= tolerance) {
+                    lParams.leftMargin = piece.xCoord;
+                    lParams.topMargin = piece.yCoord;
+                    piece.setLayoutParams(lParams);
+                    piece.canMove = false;
+                    sendViewToBack(piece);
+                }
+                break;
         }
 
         return true;
     }
+
+    public void sendViewToBack(final View child) {
+        final ViewGroup parent = (ViewGroup)child.getParent();
+        if (null != parent) {
+            parent.removeView(child);
+            parent.addView(child, 0);
+        }
+    }
 }

app/src/main/res/layout/activity_main.xml

@@ -21,7 +21,8 @@
         app:layout_constraintRight_toRightOf="parent"
         app:layout_constraintStart_toStartOf="parent"
         app:layout_constraintTop_toTopOf="parent"
-        app:srcCompat="@drawable/photo" />
+        app:srcCompat="@drawable/photo"
+        android:alpha="0.5" />
 
     <RelativeLayout
         android:id="@+id/layout"