Posted by Takeshi Hagikura, Developer Programs Engineer
At Google I/O last year we announced
ConstraintLayout, which enables you to build complex layouts while maintaining a flat view hierarchy. It is also fully supported in Android Studio's
Visual Layout Editor.
At the same time, we open sourced
FlexboxLayout to bring the same functionalities of the
CSS Flexible Layout module to Android. Here are some cases where
FlexboxLayout is particularly effective.
FlexboxLayout can be interpreted as an advanced LinearLayout because both layouts align their child views sequentially. The significant difference between LinearLayout and
FlexboxLayout is that
FlexboxLayout has a feature for wrapping.
That means if you add the
flexWrap="wrap" attribute,
FlexboxLayout puts a view to a new line if there is not enough space left in the current line as shown in the picture below.
One layout for various screen sizes
With that characteristic in mind, let's take a case where you want to put views sequentially but have them move to new lines if the available space changes (due to a device factor, orientation changes or the window resizing in the multi-window mode).
Pixel C with multi window mode enabled, divider line on the left.
Pixel C with multi window mode enabled, divider line on the middle.
Pixel C with multi window mode enabled, divider line on the right.
You would need to define multiple DP-bucket layouts (such as layout-600dp, layout-720dp, layout-1020dp) to handle various screen sizes with traditional layouts such as
LinearLayout or
RelativeLayout. But the dialog above is built with a single
FlexboxLayout.
The technique used in the example is setting the
flexWrap="wrap" as explained above,
android:layout_width="match_parent"
android:layout_height="wrap_content"
app:flexwrap="wrap">
then you can get the following layout where child views are aligned to a new line instead of overflowing its parent.
Another technique I'd like to highlight is setting the
layout_flexGrow attribute to an individual child. This helps improve the look of the final layout when free space is left over. The
layout_flexGrow attribute works similar to the
layout_weight attribute in
LinearLayout. That means
FlexboxLayout will distribute the remaining space according to the
layout_flexGrow value set to each child in the same line.
In the example below, it assumes each child has the
layout_flexGrow attribute set to
1, so free space will be evenly distributed to each of them.
android:layout_width="100dp"
android:layout_height="wrap_content"
app:layout_flexgrow="1">
You can check out the complete
layout xml file in the GitHub repository.
RecyclerView integration
Another advantage of
FlexboxLayout is that it can be integrated with
RecyclerView. With the latest release of the
alpha version the new
FlexboxLayoutManager extends
RecyclerView.LayoutManager, now you can make use of the Flexbox functionalities in a scrollable container in much more memory-efficient way.
Note that you can still achieve a scrollable Flexbox container with
FlexboxLayout wrapped with
ScrollView. But, you will be likely to experience jankiness or even an OutOfMemoryError if the number of items contained in the layout is large, as
FlexboxLayout doesn't take view recycling into account for the views that go off the screen as the user scrolls.
(If you would like to learn more about the RecyclerView in details, you can check out the videos from the Android UI toolkit team such as
1,
2)
A real world example where the
RecyclerView integration is useful is for apps like the Google Photos app or News apps, both expect large number of items while needing to handle various width of items.
One example is found in the
demo application in the
FlexboxLayout repository. As you can see in the repository, each image shown in
RecyclerView has a different width. But by setting the flexWrap setting to wrap,
FlexboxLayoutManager layoutManager = new FlexboxLayoutManager();
layoutManager.setFlexWrap(FlexWrap.WRAP);
and setting the
flexGrow (as you can see, you can configure the attributes through
FlexboxLayoutManager and
FlexboxLayoutManager.LayoutParams for child attributes instead of configuring it from xml) attribute to a positive value for each child,
void bindTo(Drawable drawable) {
mImageView.setImageDrawable(drawable);
ViewGroup.LayoutParams lp = mImageView.getLayoutParams();
if (lp instanceof FlexboxLayoutManager.LayoutParams) {
FlexboxLayoutManager.LayoutParams flexboxLp =
(FlexboxLayoutManager.LayoutParams) mImageView.getLayoutParams();
flexboxLp.setFlexGrow(1.0f);
}
}
you can see every image fits within the layout nicely regardless of the screen orientation.
If you would like to see complete FlexboxLayout example, you can check:
What's next?
Check out the full
documentation for other attributes to build flexible layouts tailored for your needs. We're very open to hear your feedback, if you find any issues or feature requests, please file an
issue on the GitHub repository.
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