Add TouchExpander

app/src/main/java/org/solovyev/android/calculator/view/TouchExpander.java

@@ -0,0 +1,85 @@
+package org.solovyev.android.calculator.view;
+
+import android.graphics.Rect;
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
+import android.support.annotation.Px;
+import android.support.v4.view.ViewCompat;
+import android.view.TouchDelegate;
+import android.view.View;
+import android.view.ViewTreeObserver;
+
+public class TouchExpander implements ViewTreeObserver.OnGlobalLayoutListener {
+
+    @NonNull
+    private final View mView;
+    @NonNull
+    private final Rect mExtra;
+    // non-null when a TouchDelegate has been set
+    @Nullable
+    private View mParent;
+
+    private TouchExpander(@NonNull View view, @Px int extra) {
+        this(view, new Rect(extra, extra, extra, extra));
+    }
+
+    private TouchExpander(@NonNull View view, @NonNull Rect extra) {
+        mView = view;
+        mExtra = extra;
+
+        attach();
+    }
+
+    private static void outset(@NonNull Rect rect, @NonNull Rect diff) {
+        rect.left -= diff.left;
+        rect.top -= diff.top;
+        rect.right += diff.right;
+        rect.bottom += diff.bottom;
+    }
+
+    @NonNull
+    public static TouchExpander attach(@NonNull View view, @Px int extra) {
+        return new TouchExpander(view, extra);
+    }
+
+    @NonNull
+    public static TouchExpander attach(@NonNull View view, @NonNull Rect extra) {
+        return new TouchExpander(view, extra);
+    }
+
+    private void attach() {
+        if (ViewCompat.isLaidOut(mView)) {
+            onLaidOut();
+            return;
+        }
+        mView.getViewTreeObserver().addOnGlobalLayoutListener(this);
+    }
+
+    @Override
+    public void onGlobalLayout() {
+        if (!ViewCompat.isLaidOut(mView)) return;
+        mView.getViewTreeObserver().removeOnGlobalLayoutListener(this);
+
+        onLaidOut();
+    }
+
+    private void onLaidOut() {
+        if (!ViewCompat.isLaidOut(mView)) {
+            throw new IllegalStateException("View is not laid out");
+        }
+        final Rect hitRect = new Rect();
+        mView.getHitRect(hitRect);
+        outset(hitRect, mExtra);
+
+        mParent = (View) mView.getParent();
+        mParent.setTouchDelegate(new TouchDelegate(hitRect, mView));
+    }
+
+    public void detach() {
+        mView.getViewTreeObserver().removeOnGlobalLayoutListener(this);
+        if (mParent != null) {
+            mParent.setTouchDelegate(null);
+            mParent = null;
+        }
+    }
+}