SpaceItemDecoration.kt

import android.graphics.Rect
import android.support.annotation.DimenRes
import android.support.annotation.Dimension
import android.support.v7.widget.GridLayoutManager
import android.support.v7.widget.LinearLayoutManager
import android.support.v7.widget.RecyclerView
import android.view.View

/**
 * Use this class to easily add space between items in a RecyclerView. Just instantiate a new
 * instance of the Builder class and you'll be good to go.
 */
abstract class SpaceItemDecoration internal constructor(
        @Dimension protected val betweenSpacing: Int,
        @Dimension protected val endSpacing: Int,
        @Dimension protected val startSpacing: Int,
        protected val recyclerView: RecyclerView,
        protected val columns: Int
) : RecyclerView.ItemDecoration() {

    override fun getItemOffsets(outRect: Rect, view: View, parent: RecyclerView,
            state: RecyclerView.State?) {
        super.getItemOffsets(outRect, view, parent, state)

        val position = recyclerView.getChildAdapterPosition(view)

        if (position != RecyclerView.NO_POSITION) {
            val adapter = recyclerView.adapter
            getItemOffsets(outRect, position, adapter?.itemCount ?: 0)
        }
    }

    protected abstract fun getItemOffsets(outRect: Rect, position: Int, count: Int)


    private class HorizontalGridSpaceItemDecoration internal constructor(
            @Dimension betweenSpacing: Int,
            @Dimension endSpacing: Int,
            @Dimension startSpacing: Int,
            recyclerView: RecyclerView,
            columns: Int
    ) : SpaceItemDecoration(
            betweenSpacing,
            endSpacing,
            startSpacing,
            recyclerView,
            columns
    ) {

        override fun getItemOffsets(outRect: Rect, position: Int, count: Int) {
            val column = position % columns

            if (startSpacing > 0) {
                if (position < columns) {
                    outRect.left = startSpacing
                }

                if (position + 1 == count) {
                    outRect.top = startSpacing
                }

                if (column != 0) {
                    outRect.bottom = betweenSpacing / 2
                }

                if (column + 1 != columns) {
                    outRect.left = betweenSpacing / 2
                }
            } else {
                outRect.top = column * betweenSpacing / columns
                outRect.bottom = betweenSpacing - (column + 1) * betweenSpacing / columns

                if (position >= columns) {
                    outRect.left = betweenSpacing
                }
            }
        }

    }


    private class HorizontalLinearSpaceItemDecoration internal constructor(
            @Dimension betweenSpacing: Int,
            @Dimension endSpacing: Int,
            @Dimension startSpacing: Int,
            recyclerView: RecyclerView,
            columns: Int
    ) : SpaceItemDecoration(
            betweenSpacing,
            endSpacing,
            startSpacing,
            recyclerView,
            columns
    ) {

        override fun getItemOffsets(outRect: Rect, position: Int, count: Int) {
            if (startSpacing > 0 || endSpacing > 0) {
                if (position == 0) {
                    outRect.left = startSpacing
                }

                if (position + 1 == count) {
                    outRect.right = endSpacing
                } else {
                    outRect.right = betweenSpacing
                }
            } else if (position + 1 != count) {
                outRect.right = betweenSpacing
            }
        }

    }


    private class VerticalGridSpaceItemDecoration internal constructor(
            @Dimension betweenSpacing: Int,
            @Dimension endSpacing: Int,
            @Dimension startSpacing: Int,
            recyclerView: RecyclerView,
            columns: Int
    ) : SpaceItemDecoration(
            betweenSpacing,
            endSpacing,
            startSpacing,
            recyclerView,
            columns
    ) {

        override fun getItemOffsets(outRect: Rect, position: Int, count: Int) {
            val column = position % columns

            if (startSpacing > 0 || endSpacing > 0) {
                if (position < columns) {
                    outRect.top = startSpacing
                }

                if (position + 1 == count) {
                    outRect.bottom = endSpacing
                } else {
                    outRect.bottom = betweenSpacing
                }

                if (column != 0) {
                    outRect.left = betweenSpacing / 2
                }

                if (column + 1 != columns) {
                    outRect.right = betweenSpacing / 2
                }
            } else {
                outRect.left = column * betweenSpacing / columns
                outRect.right = betweenSpacing - (column + 1) * betweenSpacing / columns

                if (position >= columns) {
                    outRect.top = betweenSpacing
                }
            }
        }

    }


    private class VerticalLinearSpaceItemDecoration internal constructor(
            @Dimension betweenSpacing: Int,
            @Dimension endSpacing: Int,
            @Dimension startSpacing: Int,
            recyclerView: RecyclerView,
            columns: Int
    ) : SpaceItemDecoration(
            betweenSpacing,
            endSpacing,
            startSpacing,
            recyclerView,
            columns
    ) {

        override fun getItemOffsets(outRect: Rect, position: Int, count: Int) {
            if (startSpacing > 0 || endSpacing > 0) {
                if (position == 0) {
                    outRect.top = startSpacing
                }

                if (position + 1 == count) {
                    outRect.bottom = endSpacing
                } else {
                    outRect.bottom = betweenSpacing
                }
            } else if (position + 1 != count) {
                outRect.bottom = betweenSpacing
            }
        }

    }


    class Builder(private val recyclerView: RecyclerView) {
        @Dimension private var betweenSpacing: Int = 0
        @Dimension private var endSpacing: Int = 0
        @Dimension private var startSpacing: Int = 0

        fun build(): SpaceItemDecoration {
            val lm = recyclerView.layoutManager

            return if (lm == null) {
                throw NullPointerException("recyclerView must have a LayoutManager")
            } else if (lm is GridLayoutManager) {
                if (lm.orientation == GridLayoutManager.HORIZONTAL) {
                    HorizontalGridSpaceItemDecoration(betweenSpacing, endSpacing, startSpacing,
                            recyclerView, lm.spanCount)
                } else {
                    VerticalGridSpaceItemDecoration(betweenSpacing, endSpacing, startSpacing,
                            recyclerView, lm.spanCount)
                }
            } else if (lm is LinearLayoutManager) {
                if (lm.orientation == LinearLayoutManager.HORIZONTAL) {
                    HorizontalLinearSpaceItemDecoration(betweenSpacing, endSpacing, startSpacing,
                            recyclerView, 1)
                } else {
                    VerticalLinearSpaceItemDecoration(betweenSpacing, endSpacing, startSpacing,
                            recyclerView, 1)
                }
            } else {
                throw IllegalArgumentException("the given LayoutManager (" +
                        lm.javaClass.simpleName + ") isn't a supported type")
            }
        }

        fun setBetweenSpacing(@Dimension betweenSpacing: Int): Builder {
            this.betweenSpacing = betweenSpacing
            return this
        }

        fun setBetweenSpacingResId(@DimenRes betweenSpacingResId: Int): Builder {
            setBetweenSpacing(recyclerView.resources.getDimensionPixelSize(betweenSpacingResId))
            return this
        }

        fun setEndSpacing(@Dimension endSpacing: Int): Builder {
            this.endSpacing = endSpacing
            return this
        }

        fun setEndSpacingResId(@DimenRes endSpacingResId: Int): Builder {
            setEndSpacing(recyclerView.resources.getDimensionPixelSize(endSpacingResId))
            return this
        }

        fun setStartSpacing(@Dimension startSpacing: Int): Builder {
            this.startSpacing = startSpacing
            return this
        }

        fun setStartSpacingResId(@DimenRes startSpacingResId: Int): Builder {
            setStartSpacing(recyclerView.resources.getDimensionPixelSize(startSpacingResId))
            return this
        }
    }

}