rajumark · November 5, 2019 06:12 · Jan 14, 2016
diff --git a/SightFragment.java b/SightFragment.java
@@ -0,0 +1,90 @@
+package cc.cubone.turbo.core.app;
+
+import android.os.Bundle;
+import android.support.v4.app.Fragment;
+import android.view.View;
+
+/**
+ * Fragment for handling view after it has been created and visible to user for the first time.
+ *
+ * <p>Specially in {@link android.support.v4.view.ViewPager}, the page will be created beforehand
+ * but not be visible to user.
+ *
+ * <p>Call {@link android.support.v4.view.ViewPager#setOffscreenPageLimit(int)} to set the number of
+ * pages that should be retained.
+ *
+ * Reference:
+ * <ul>
+ * <li><a href="http://stackoverflow.com/questions/10024739/how-to-determine-when-fragment-becomes-visible-in-viewpager">
+ * How to determine when Fragment becomes visible in ViewPager</a>
+ * </ul>
+ */
+public class SightFragment extends Fragment {
+
+    private boolean mUserSeen = false;
+    private boolean mViewCreated = false;
+
+    public SightFragment() {
+    }
+
+    /*public boolean isUserSeen() {
+        return mUserSeen;
+    }
+
+    public boolean isViewCreated() {
+        return mViewCreated;
+    }*/
+
+    @Override
+    public void setUserVisibleHint(boolean isVisibleToUser) {
+        super.setUserVisibleHint(isVisibleToUser);
+        if (!mUserSeen && isVisibleToUser) {
+            mUserSeen = true;
+            onUserFirstSight();
+            tryViewCreatedFirstSight();
+        }
+        onUserVisibleChanged(isVisibleToUser);
+    }
+
+    @Override
+    public void onViewCreated(View view, Bundle savedInstanceState) {
+        // Override this if you want to get savedInstanceState.
+        mViewCreated = true;
+        tryViewCreatedFirstSight();
+    }
+
+    @Override
+    public void onDestroyView() {
+        super.onDestroyView();
+        mViewCreated = false;
+        mUserSeen = false;
+    }
+
+    private void tryViewCreatedFirstSight() {
+        if (mUserSeen && mViewCreated) {
+            onViewCreatedFirstSight(getView());
+        }
+    }
+
+    /**
+     * Called when the new created view is visible to user for the first time.
+     */
+    protected void onViewCreatedFirstSight(View view) {
+        // handling here
+    }
+
+    /**
+     * Called when the fragment's UI is visible to user for the first time.
+     *
+     * <p>However, the view may not be created currently if in {@link android.support.v4.view.ViewPager}.
+     */
+    protected void onUserFirstSight() {
+    }
+
+    /**
+     * Called when the visible state to user has been changed.
+     */
+    protected void onUserVisibleChanged(boolean visible) {
+    }
+
+}