Added verification on show tooltip to prevent crash if root view is not showing. Fixes #9

Author: douglasjunior

library/src/main/java/io/github/douglasjunior/androidSimpleTooltip/SimpleTooltip.java

@@ -42,6 +42,7 @@
 import android.support.annotation.IdRes;
 import android.support.annotation.LayoutRes;
 import android.support.annotation.StringRes;
+import android.util.Log;
 import android.view.Gravity;
 import android.view.LayoutInflater;
 import android.view.MotionEvent;
@@ -65,6 +66,8 @@
 @SuppressWarnings("SameParameterValue")
 public class SimpleTooltip implements PopupWindow.OnDismissListener {
 
+    private static final String TAG = SimpleTooltip.class.getSimpleName();
+
     // Default Resources
     private static final int mDefaultPopupWindowStyleRes = android.R.attr.popupWindowStyle;
     private static final int mDefaultTextAppearanceRes = R.style.simpletooltip_default;
@@ -164,7 +167,10 @@ public void show() {
         mRootView.post(new Runnable() {
             @Override
             public void run() {
-                mPopupWindow.showAtLocation(mRootView, Gravity.NO_GRAVITY, mRootView.getWidth(), mRootView.getHeight());
+                if (mRootView.isShown())
+                    mPopupWindow.showAtLocation(mRootView, Gravity.NO_GRAVITY, mRootView.getWidth(), mRootView.getHeight());
+                else
+                    Log.e(TAG, "Tooltip cannot be shown, root view is invalid or has been closed.");
             }
         });
     }