AutoGridfitLayoutManager.java

package me.qixingchen.mdbilibili.widget;

import android.content.Context;
import android.support.v7.widget.GridLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.util.TypedValue;

/**
 * Created by qixingchen on 15/12/3.
 * 自动适配网格布局的非滑动方向上项目的数量
 */
public class AutoGridfitLayoutManager extends GridLayoutManager {
    private int mColumnWidth;
    private boolean mColumnWidthChanged = true;

    public AutoGridfitLayoutManager(Context context, int dpWidth) {
        /* Initially set spanCount to 1, will be changed automatically later. */
        super(context, 1);
        setColumnWidth(checkedColumnWidth(context, (int) (dpWidth * context.getApplicationContext().getResources().getDisplayMetrics().density)));
    }

    public AutoGridfitLayoutManager(Context context, int dpWidth, int orientation, boolean reverseLayout) {
        /* Initially set spanCount to 1, will be changed automatically later. */
        super(context, 1, orientation, reverseLayout);
        setColumnWidth(checkedColumnWidth(context, (int) (dpWidth * context.getApplicationContext().getResources().getDisplayMetrics().density)));
    }

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