SpannedGridLayoutManager

SpannedGridLayouManager is a layout manager that will resize and reorder views based on a provided SpanSize.

IMPORTANT: as the goal of this LayoutManager is to fill all gaps if possible, views may be placed in an order which may not be related to their positions. That is, if View #9 can fill a gap before View #8, it will be placed in an previous position, ignoring the normal ordering.

Usage

Gradle dependency:

dependencies {
  compile 'com.arasthel:spannedgridlayoutmanager:2.0.1' 
}

When you create a new SpannedGridLayoutManager you must provide:

An Orientation: Orientation.VERTICAL or Orientation.HORIZONTAL.
The span count to divide the layout.

Kotlin Example:

val spannedGridLayoutManager = SpannedGridLayoutManager(

  orientation = SpannedGridLayoutManager.Orientation.VERTICAL,

spans = 4) recyclerview.layoutManager = spannedGridLayoutManager

Java Example:

SpannedGridLayoutManager spannedGridLayoutManager = new SpannedGridLayoutManager(
 SpannedGridLayoutManager.Orientation.VERTICAL, 4);
 recyclerview.setLayoutManager(spannedGridLayoutManager);

To set the SpanSize for each view, you would do it on the RecyclerView.Adapter. I would do it in onBindViewHolder method, since you have access to position and can use several sizes depending on the position or your model's data.

Kotlin:

override fun onBindViewHolder(holder: ViewHolder, position: Int) {

  val width = 1
  val height = 2

holder.itemView.layoutParams = SpanLayoutParams(SpanSize(width, height)) 
}

Java:

@Override public void onBindViewHolder(ViewHolder holder, int position) {

  int width = 1;
  int height = 2;

holder.itemView.setLayoutParams(new SpanLayoutParams(new SpanSize(width, height)));
 
}

About restoring scroll position:

As this LayoutManager may change the order in screen of its items, it has some issues with restoring scroll position when the sizes of the items change drastically. To work around this, restoring the scroll position when recreating this LayoutManager is disabled by default.

If you are sure that the position of the items won't change much, you can enable it again using:

spannedLayoutManager.itemOrderIsStable = true

Migrating from 1.X to 2.X

Due to critical layout issues, the API for using SpanSizes had to change. The only changes you should have to do in your code are:

 val width = 1
  val height = 2

// OLD
  // holder.itemView.layoutParams = RecyclerView.LayoutParams(width, height)

// NEW
  holder.itemView.layoutParams = SpanLayoutParams(SpanSize(width, height))

Just use the new SpanLayoutParams instead of generic RecyclerView.LayoutParams.

Animations

To have animations as shown in the sample, you must:

Use setHasStableIds(true) in your adapter.
Override getItemId method to return a stable id - that is, it won't change for the same position.
Use adapter.notifyDatasetChanged() to trigger the layout process.

Implementation details

This library uses Rects to find the empty gaps and choose where a view will be placed. The underlying algorithm is explained in this paper.

Initially, there will be 1 free-space Rect (0, 0, spanCount, Int.MAX_VALUE) for Orientation.VERTICAL or (0, 0, Int.MAX_VALUE, spanCount) for Orientation.HORIZONTAL.
When a view must added, it will search for the free rects that are adjacent to the view's Rect or that intersects it.
It will iterate over these rects looking for those that are adjacent to the view and don't contain it, which will be stored. If a rect doesn't match this criteria, it will be removed from the list of free rects and divided in 4 possible sub-rects - left, top, right, bottom - like this:

For each of that subrects, if none of the previously stored adjacent free rects and none of the rects in the list of free rects intersects with it, it will be added to this list as a valid free rect.

You can see this code in SpannedGridLayoutManager's subtract(Rect) method.

License - MIT

MIT License  Copyright © 2017 Jorge Martín Espinosa  Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:  The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

SpannedGridLayoutManager