RecyclerView GridLayoutManager: how to auto-detect

问题:

Using the new GridLayoutManager: https://developer.android.com/reference/android/support/v7/widget/GridLayoutManager.html

It takes an explicit span count, so the problem now becomes: how do you know how many "spans" fit per row? This is a grid, after all. There should be as many spans as the RecyclerView can fit, based on measured width.

Using the old GridView, you would just set the "columnWidth" property and it would automatically detect how many columns fit. This is basically what I want to replicate for the RecyclerView:

• add OnLayoutChangeListener on the RecyclerView
• in this callback, inflate a single 'grid item' and measure it
• spanCount = recyclerViewWidth / singleItemWidth;

This seems like pretty common behavior, so is there a simpler way that I'm not seeing?

回答1:

Personaly I don't like to subclass RecyclerView for this, because for me it seems that there is GridLayoutManager's responsibility to detect span count. So after some android source code digging for RecyclerView and GridLayoutManager I wrote my own class extended GridLayoutManager that do the job:

public class GridAutofitLayoutManager extends GridLayoutManager
{
    private int mColumnWidth;
    private boolean mColumnWidthChanged = true;

    public GridAutofitLayoutManager(Context context, int columnWidth)
    {
        /* Initially set spanCount to 1, will be changed automatically later. */
        super(context, 1);
        setColumnWidth(checkedColumnWidth(context, columnWidth));
    }

    public GridAutofitLayoutManager(Context context, int columnWidth, int orientation, boolean reverseLayout)
    {
        /* Initially set spanCount to 1, will be changed automatically later. */
        super(context, 1, orientation, reverseLayout);
        setColumnWidth(checkedColumnWidth(context, columnWidth));
    }

    private int checkedColumnWidth(Context context, int columnWidth)
    {
        if (columnWidth <= 0)
        {
            /* Set default columnWidth value (48dp here). It is better to move this constant
            to static constant on top, but we need context to convert it to dp, so can't really
            do so. */
            columnWidth = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 48,
                    context.getResources().getDisplayMetrics());
        }
        return columnWidth;
    }

    public void setColumnWidth(int newColumnWidth)
    {
        if (newColumnWidth > 0 && newColumnWidth != mColumnWidth)
        {
            mColumnWidth = newColumnWidth;
            mColumnWidthChanged = true;
        }
    }

    @Override
    public void onLayoutChildren(RecyclerView.Recycler recycler, RecyclerView.State state)
    {
        int width = getWidth();
        int height = getHeight();
        if (mColumnWidthChanged && mColumnWidth > 0 && width > 0 && height > 0)
        {
            int totalSpace;
            if (getOrientation() == VERTICAL)
            {
                totalSpace = width - getPaddingRight() - getPaddingLeft();
            }
            else
            {
                totalSpace = height - getPaddingTop() - getPaddingBottom();
            }
            int spanCount = Math.max(1, totalSpace / mColumnWidth);
            setSpanCount(spanCount);
            mColumnWidthChanged = false;
        }
        super.onLayoutChildren(recycler, state);
    }
}

I don't actually remember why I choosed to set span count in onLayoutChildren, I wrote this class some time ago. But the point is we need to do so after view get measured. so we can get it's height and width.

EDIT: Fix error in code caused to incorrectly setting span count. Thanks user @Elyees Abouda for reporting and suggesting solution.

回答2:

I accomplished this using a view tree observer to get the width of the recylcerview once rendered and then getting the fixed dimensions of my card view from resources and then setting the span count after doing my calculations. It is only really applicable if the items you are displaying are of a fixed width. This helped me automatically populate the grid regardless of screen size or orientation.

mRecyclerView.getViewTreeObserver().addOnGlobalLayoutListener(
            new ViewTreeObserver.OnGlobalLayoutListener() {
                @Override
                public void onGlobalLayout() {
                    mRecyclerView.getViewTreeObserver().removeOnGLobalLayoutListener(this);
                    int viewWidth = mRecyclerView.getMeasuredWidth();
                    float cardViewWidth = getActivity().getResources().getDimension(R.dimen.cardview_layout_width);
                    int newSpanCount = (int) Math.floor(viewWidth / cardViewWidth);
                    mLayoutManager.setSpanCount(newSpanCount);
                    mLayoutManager.requestLayout();
                }
            });

回答3:

I extended the RecyclerView and overrode the onMeasure method.

I set an item width(member variable) as early as I can,with a default of 1. This also updates on configuration changed. This will now have as many rows as can fit in portrait,landscape,phone/tablet etc.

@Override
protected void onMeasure(int widthSpec, int heightSpec) {
    super.onMeasure(widthSpec, heightSpec);
    int width = MeasureSpec.getSize(widthSpec);
    if(width != 0){
        int spans = width / mItemWidth;
        if(spans > 0){
            mLayoutManager.setSpanCount(spans);
        }
    }
}

回答4:

Well, this is what I used, fairly basic, but gets the job done for me. This code basically gets the screen width in dips and then divides by 300 (or whatever width you're using for your adapter's layout). So smaller phones with 300-500 dip width only display one column, tablets 2-3 columns etc. Simple, fuss free and without downside, as far as I can see.

Display display = getActivity().getWindowManager().getDefaultDisplay();
DisplayMetrics outMetrics = new DisplayMetrics();
display.getMetrics(outMetrics);

float density  = getResources().getDisplayMetrics().density;
float dpWidth  = outMetrics.widthPixels / density;
int columns = Math.round(dpWidth/300);
mLayoutManager = new GridLayoutManager(getActivity(),columns);
mRecyclerView.setLayoutManager(mLayoutManager);

回答5:

I'm posting this just in case someone gets weird column width as in my case.

I'm not able to comment on @s-marks's answer due to my low reputation. I applied his solution solution but I got some weird column width, so I modified checkedColumnWidth function as follows:

private int checkedColumnWidth(Context context, int columnWidth)
{
    if (columnWidth <= 0)
    {
        /* Set default columnWidth value (48dp here). It is better to move this constant
        to static constant on top, but we need context to convert it to dp, so can't really
        do so. */
        columnWidth = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 48,
                context.getResources().getDisplayMetrics());
    }

    else
    {
        columnWidth = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, columnWidth,
                context.getResources().getDisplayMetrics());
    }
    return columnWidth;
}

By converting the given column width into DP fixed the issue.

回答6:

The upvoted solution is fine, but handles the incoming values as pixels, which can trip you up if you're hardcoding values for testing and assuming dp. Easiest way is probably to put the column width in a dimension and read it when configuring the GridAutofitLayoutManager, which will automatically convert dp to correct pixel value:

new GridAutofitLayoutManager(getActivity(), (int)getActivity().getResources().getDimension(R.dimen.card_width))

回答7:

I conclusion above answers here

回答8:

To accommodate orientation change on s-marks's answer, I added a check on width change (width from getWidth(), not column width).

private boolean mWidthChanged = true;
private int mWidth;


@Override
public void onLayoutChildren(RecyclerView.Recycler recycler, RecyclerView.State state)
{
    int width = getWidth();
    int height = getHeight();

    if (width != mWidth) {
        mWidthChanged = true;
        mWidth = width;
    }

    if (mColumnWidthChanged && mColumnWidth > 0 && width > 0 && height > 0
            || mWidthChanged)
    {
        int totalSpace;
        if (getOrientation() == VERTICAL)
        {
            totalSpace = width - getPaddingRight() - getPaddingLeft();
        }
        else
        {
            totalSpace = height - getPaddingTop() - getPaddingBottom();
        }
        int spanCount = Math.max(1, totalSpace / mColumnWidth);
        setSpanCount(spanCount);
        mColumnWidthChanged = false;
        mWidthChanged = false;
    }
    super.onLayoutChildren(recycler, state);
}

回答9:

1. Set minimal fixed width of imageView (144dp x 144dp for example)

2. When you create GridLayoutManager, you need to know how much columns will be with minimal size of imageView:

   WindowManager wm = (WindowManager) this.getSystemService(Context.WINDOW_SERVICE); //Получаем размер экрана
   Display display = wm.getDefaultDisplay();
   
   Point point = new Point();
   display.getSize(point);
   int screenWidth = point.x; //Ширина экрана
   
   int photoWidth = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 144, this.getResources().getDisplayMetrics()); //Переводим в точки
   
   int columnsCount = screenWidth/photoWidth; //Число столбцов
   
   GridLayoutManager gridLayoutManager = new GridLayoutManager(this, columnsCount);
   recyclerView.setLayoutManager(gridLayoutManager);
   

3. After that you need to resize imageView in adapter if you have space in column. You may send newImageViewSize then inisilize adapter from activity there you calculate screen and column count:

   @Override //Заполнение нашей плитки
   public void onBindViewHolder(PhotoHolder holder, int position) {
      ...
      ViewGroup.LayoutParams photoParams = holder.photo.getLayoutParams(); //Параметры нашей фотографии
   
      int newImageViewSize = screenWidth/columnsCount; //Новый размер фотографии
   
      photoParams.width = newImageViewSize; //Установка нового размера
      photoParams.height = newImageViewSize;
      holder.photo.setLayoutParams(photoParams); //Установка параметров
      ...
   }
   

It works in both orientations. In vertical I have 2 columns and in horizontal - 4 columns. The result: https://i.stack.imgur.com/WHvyD.jpg

回答10:

This is s.maks' class with a minor fix for when the recyclerview itself changes size. Such as when you deal with the orientation changes yourself (in the manifest android:configChanges="orientation|screenSize|keyboardHidden"), or some other reason the recyclerview might change size without the mColumnWidth changing. I also changed the int value it takes to be the resource of the size and allowed a constructor of no resource then setColumnWidth to do that yourself.

public class GridAutofitLayoutManager extends GridLayoutManager {
    private Context context;
    private float mColumnWidth;

    private float currentColumnWidth = -1;
    private int currentWidth = -1;
    private int currentHeight = -1;


    public GridAutofitLayoutManager(Context context) {
        /* Initially set spanCount to 1, will be changed automatically later. */
        super(context, 1);
        this.context = context;
        setColumnWidthByResource(-1);
    }

    public GridAutofitLayoutManager(Context context, int resource) {
        this(context);
        this.context = context;
        setColumnWidthByResource(resource);
    }

    public GridAutofitLayoutManager(Context context, int resource, int orientation, boolean reverseLayout) {
        /* Initially set spanCount to 1, will be changed automatically later. */
        super(context, 1, orientation, reverseLayout);
        this.context = context;
        setColumnWidthByResource(resource);
    }

    public void setColumnWidthByResource(int resource) {
        if (resource >= 0) {
            mColumnWidth = context.getResources().getDimension(resource);
        } else {
            /* Set default columnWidth value (48dp here). It is better to move this constant
            to static constant on top, but we need context to convert it to dp, so can't really
            do so. */
            mColumnWidth = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 48,
                    context.getResources().getDisplayMetrics());
        }
    }

    public void setColumnWidth(float newColumnWidth) {
        mColumnWidth = newColumnWidth;
    }

    @Override
    public void onLayoutChildren(RecyclerView.Recycler recycler, RecyclerView.State state) {
        recalculateSpanCount();
        super.onLayoutChildren(recycler, state);
    }

    public void recalculateSpanCount() {
        int width = getWidth();
        if (width <= 0) return;
        int height = getHeight();
        if (height <= 0) return;
        if (mColumnWidth <= 0) return;
        if ((width != currentWidth) || (height != currentHeight) || (mColumnWidth != currentColumnWidth)) {
            int totalSpace;
            if (getOrientation() == VERTICAL) {
                totalSpace = width - getPaddingRight() - getPaddingLeft();
            } else {
                totalSpace = height - getPaddingTop() - getPaddingBottom();
            }
            int spanCount = (int) Math.max(1, Math.floor(totalSpace / mColumnWidth));
            setSpanCount(spanCount);
            currentColumnWidth = mColumnWidth;
            currentWidth = width;
            currentHeight = height;
        }
    }
}

回答11:

Set spanCount to a large number (which is the max number of column) and set a custom SpanSizeLookup to the GridLayoutManager.

mLayoutManager.setSpanSizeLookup(new GridLayoutManager.SpanSizeLookup() {
    @Override
    public int getSpanSize(int i) {
        return SPAN_COUNT / (int) (mRecyclerView.getMeasuredWidth()/ CELL_SIZE_IN_PX);
    }
});

It's a bit ugly, but it work.

I think a manager like AutoSpanGridLayoutManager would be the best solution, but i didn't find anything like that.

EDIT : There is a bug, on some device it add blank space to the right

回答12:

Here's the relevant parts of a wrapper I've been using to auto-detect the span count. You initialize it by calling setGridLayoutManager with a R.layout.my_grid_item reference, and it figures out how many of those can fit on each row.

public class AutoSpanRecyclerView extends RecyclerView {
    private int     m_gridMinSpans;
    private int     m_gridItemLayoutId;
    private LayoutRequester m_layoutRequester = new LayoutRequester();

    public void setGridLayoutManager( int orientation, int itemLayoutId, int minSpans ) {
        GridLayoutManager layoutManager = new GridLayoutManager( getContext(), 2, orientation, false );
        m_gridItemLayoutId = itemLayoutId;
        m_gridMinSpans = minSpans;

        setLayoutManager( layoutManager );
    }

    @Override
    protected void onLayout( boolean changed, int left, int top, int right, int bottom ) {
        super.onLayout( changed, left, top, right, bottom );

        if( changed ) {
            LayoutManager layoutManager = getLayoutManager();
            if( layoutManager instanceof GridLayoutManager ) {
                final GridLayoutManager gridLayoutManager = (GridLayoutManager) layoutManager;
                LayoutInflater inflater = LayoutInflater.from( getContext() );
                View item = inflater.inflate( m_gridItemLayoutId, this, false );
                int measureSpec = View.MeasureSpec.makeMeasureSpec( 0, View.MeasureSpec.UNSPECIFIED );
                item.measure( measureSpec, measureSpec );
                int itemWidth = item.getMeasuredWidth();
                int recyclerViewWidth = getMeasuredWidth();
                int spanCount = Math.max( m_gridMinSpans, recyclerViewWidth / itemWidth );

                gridLayoutManager.setSpanCount( spanCount );

                // if you call requestLayout() right here, you'll get ArrayIndexOutOfBoundsException when scrolling
                post( m_layoutRequester );
            }
        }
    }

    private class LayoutRequester implements Runnable {
        @Override
        public void run() {
            requestLayout();
        }
    }
}