No jump menu when cannot jump pages

app/src/main/java/com/hippo/ehviewer/ui/scene/GalleryPreviewsScene.java

@@ -45,6 +45,7 @@ import com.hippo.ehviewer.Settings;
 import com.hippo.ehviewer.client.EhClient;
 import com.hippo.ehviewer.client.EhRequest;
 import com.hippo.ehviewer.client.EhUrl;
+import com.hippo.ehviewer.client.data.GalleryDetail;
 import com.hippo.ehviewer.client.data.GalleryInfo;
 import com.hippo.ehviewer.client.data.GalleryPreview;
 import com.hippo.ehviewer.client.data.PreviewSet;
@@ -190,11 +191,8 @@ public class GalleryPreviewsScene extends ToolbarScene {
         super.onViewCreated(view, savedInstanceState);
         setTitle(R.string.gallery_previews);
         setNavigationIcon(R.drawable.v_arrow_left_dark_x24);
-    }
-
-    @Override
-    public int getMenuResId() {
-        return R.menu.scene_gallery_previews;
+        if (((GalleryDetail)mGalleryInfo).previewPages > 2)
+            showMenu(R.menu.scene_gallery_previews);
     }
 
     @Override

app/src/main/java/com/hippo/ehviewer/ui/scene/ToolbarScene.kt

@@ -23,6 +23,7 @@ import android.view.ViewGroup
 import androidx.annotation.DrawableRes
 import androidx.annotation.StringRes
 import androidx.appcompat.widget.Toolbar
+import androidx.core.view.size
 import com.google.android.material.appbar.AppBarLayout
 import com.hippo.ehviewer.R
 
@@ -65,6 +66,18 @@ abstract class ToolbarScene : BaseScene() {
         }
     }
 
+    fun hideMenu() {
+        mToolbar?.menu?.clear()
+    }
+
+    fun showMenu(menuResId: Int) {
+        if (mToolbar?.menu?.size != 0) return
+        mToolbar?.apply {
+            inflateMenu(menuResId)
+            setOnMenuItemClickListener { item: MenuItem -> onMenuItemClick(item) }
+        }
+    }
+
     open fun getMenuResId(): Int {
         return 0
     }