RecyclerView通过使用GridLayoutManager来显示网格中的项目。
在GridView中，为了指定元素之间的间距，我会设置horizontalSpacing和verticalSpacing属性。RecyclerView上实现相同的效果？我还没有用GridLayout测试过，但对于LinearLayout，我只是为每个列表项的根布局设置了一个margin。如果你想要所有项之间有相同的空白（比如说8dp），你需要这样做：
这样每个项周围就会有一个恒定的8dp的空白。
下面的代码展示了一个横向的RecyclerView，它以8dp的正确间距显示图像：
<!-- fragment_layout.xml -->
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:padding="4dp">
<android.support.v7.widget.RecyclerView
android:id="@+id/recycler_view"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal"
app:layoutManager="android.support.v7.widget.LinearLayoutManager"
tools:listitem="@layout/list_item" />
</LinearLayout>
<!-- list_item.xml -->
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_margin="4dp">
<ImageView
android:layout_width="@dimen/thumbnail_size"
android:layout_height="@dimen/thumbnail_size"
android:contentDescription="@string/image_content_desc" />
</LinearLayout>
编辑：我意识到项目视图需要有一个父 ViewGroup，所以我更新了代码片段。
ItemDecorator来实现这个功能：public class EqualSpaceItemDecoration extends RecyclerView.ItemDecoration {
private final int mSpaceHeight;
public EqualSpaceItemDecoration(int mSpaceHeight) {
this.mSpaceHeight = mSpaceHeight;
}
@Override
public void getItemOffsets(Rect outRect, View view, RecyclerView parent,
RecyclerView.State state) {
outRect.bottom = mSpaceHeight;
outRect.top = mSpaceHeight;
outRect.left = mSpaceHeight;
outRect.right = mSpaceHeight;
}
}
RecyclerView中，可以使用ItemDecoration添加项目之间的间距。
在此之前，让我们进行一些数学计算，以找出列表项周围的边距。outRect中。如果您正确地进行了数学计算，为了保持等距和等大小，您会发现这些偏移值不是常数，它们根据列索引和行索引而改变。让我们推导出偏移值的方程式。
For 0 and 1,
d + w + a = d − a + w + c
c = 2a
For 0 and 2,
d + w + a = d − c + w + e
e = a + c
e = 3a
If you see the pattern here,
right = a, 2a, 3a, ... , (n + 1) × a
right = (nᵢ + 1) × a
na = d
a = d ÷ n
right = (nᵢ + 1) × d ÷ n
Pattern of left side,
left = d, d − a, d − 2a, d − 3a, ... , d − na
left = d − nᵢ × a
left = d − nᵢ × d ÷ n
nᵢ - Column index
在这里，我们进行数学计算时不考虑边缘。
For 0 and 1,
w + a = d − a + w + c
c = 2a − d
For 0 and 2,
w + a = d − c + w + e
e = 3a − 2d
The pattern here is,
right = a, 2a − d, 3a − 2d, ... , (n + 1) × a - nd
right = (nᵢ + 1) × a - nᵢd
(n + 1) × a − nd = 0
a = nd ÷ (n + 1)
∴ right = d − d × (nᵢ + 1) ÷ q
q = n + 1
q - Column count
nᵢ - Column index
left = 0, d − a, 2(d − a), ... , n(d − a)
left = nᵢ(d − a)
left = nᵢ × d ÷ q
class SpacingItemDecoration(
private val spacing: Int,
private val includeEdge: Boolean,
private val headerRowCount: Int = 0
) : RecyclerView.ItemDecoration() {
override fun getItemOffsets(
outRect: Rect,
view: View,
parent: RecyclerView,
state: RecyclerView.State
) {
val columnCount = getColumnCount(parent)
val position = parent.getChildAdapterPosition(view) - headerRowCount * columnCount
if (position >= 0) {
val rowCount = getRowCount(parent, columnCount)
val orientation = getOrientation(parent)
val columnIndex = position % columnCount
val rowIndex = position / columnCount
if (includeEdge) {
when (orientation) {
RecyclerView.VERTICAL -> {
outRect.left = getStartOffsetWithEdge(spacing, columnIndex, columnCount)
outRect.right = getEndOffsetWithEdge(spacing, columnIndex, columnCount)
outRect.top = getStartOffsetWithEdge(spacing, rowIndex, rowCount)
outRect.bottom = getEndOffsetWithEdge(spacing, rowIndex, rowCount)
}
RecyclerView.HORIZONTAL -> {
outRect.top = getStartOffsetWithEdge(spacing, columnIndex, columnCount)
outRect.bottom = getEndOffsetWithEdge(spacing, columnIndex, columnCount)
outRect.left = getStartOffsetWithEdge(spacing, rowIndex, rowCount)
outRect.right = getEndOffsetWithEdge(spacing, rowIndex, rowCount)
}
}
} else {
when (orientation) {
RecyclerView.VERTICAL -> {
outRect.left = getStartOffsetWithoutEdge(spacing, columnIndex, columnCount)
outRect.right = getEndOffsetWithoutEdge(spacing, columnIndex, columnCount)
outRect.top = getStartOffsetWithoutEdge(spacing, rowIndex, rowCount)
outRect.bottom = getEndOffsetWithoutEdge(spacing, rowIndex, rowCount)
}
RecyclerView.HORIZONTAL -> {
outRect.top = getStartOffsetWithoutEdge(spacing, columnIndex, columnCount)
outRect.bottom = getEndOffsetWithoutEdge(spacing, columnIndex, columnCount)
outRect.left = getStartOffsetWithoutEdge(spacing, rowIndex, rowCount)
outRect.right = getEndOffsetWithoutEdge(spacing, rowIndex, rowCount)
}
}
}
} else {
outRect.left = 0
outRect.right = 0
outRect.top = 0
outRect.bottom = 0
}
}
private fun getColumnCount(parent: RecyclerView) = when (val layoutManager = parent.layoutManager) {
is GridLayoutManager -> layoutManager.spanCount
is StaggeredGridLayoutManager -> layoutManager.spanCount
else -> 1
}
private fun getRowCount(parent: RecyclerView, columnCount: Int) =
parent.adapter?.itemCount?.div(columnCount)?.minus(headerRowCount)
private fun getOrientation(parent: RecyclerView) = when (val layoutManager = parent.layoutManager) {
is LinearLayoutManager -> layoutManager.orientation
is GridLayoutManager -> layoutManager.orientation
is StaggeredGridLayoutManager -> layoutManager.orientation
else -> RecyclerView.VERTICAL
}
private fun getStartOffsetWithEdge(spacing: Int, columnIndex: Int, columnCount: Int?): Int {
if (columnCount == null) return spacing
return spacing - spacing * columnIndex / columnCount
}
private fun getEndOffsetWithEdge(spacing: Int, columnIndex: Int, columnCount: Int?): Int {
if (columnCount == null) return 0
return spacing * (columnIndex + 1) / columnCount
}
private fun getStartOffsetWithoutEdge(spacing: Int, columnIndex: Int, columnCount: Int?): Int {
if (columnCount == null) return 0
return spacing * columnIndex / columnCount
}
private fun getEndOffsetWithoutEdge(spacing: Int, columnIndex: Int, columnCount: Int?): Int {
if (columnCount == null) return spacing
return spacing - spacing * (columnIndex + 1) / columnCount
}
}
public class EqualSpaceItemDecoration extends RecyclerView.ItemDecoration {
private final int mSpaceHeight;
public EqualSpaceItemDecoration(int mSpaceHeight) {
this.mSpaceHeight = mSpaceHeight;
}
@Override
public void getItemOffsets(Rect outRect, View view, RecyclerView parent,
RecyclerView.State state) {
outRect.bottom = mSpaceHeight;
outRect.top = mSpaceHeight;
outRect.left = mSpaceHeight;
outRect.right = mSpaceHeight;
}
public void getItemOffsets (Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
int position= parent.getChildAdapterPosition (view);
int column = position% numberOfColumns;
outRect.left= margin-column*spacingPx/numberOfColumns;
outRect.right= (column+1)* margin/numberOfColumns;
outRect.top= margin;
}
}
class ItemDecoration(space: Int) : RecyclerView.ItemDecoration() {
private val halfSpace: Int
override fun getItemOffsets(outRect: Rect,
view: View,
parent: RecyclerView,
state: RecyclerView.State) {
if (parent.paddingLeft != halfSpace) {
parent.setPadding(halfSpace, halfSpace, halfSpace, halfSpace)
parent.clipToPadding = false
}
outRect.top = halfSpace
outRect.bottom = halfSpace
outRect.left = halfSpace
outRect.right = halfSpace
}
init {
halfSpace = space / 2
}
}
在RecyclerView中的实现:
rvFeeds.apply {
layoutManager = mLM
adapter = mAdapter
itemAnimator = null
addItemDecoration(ItemDecoration(resources.getDimension(R.dimen.margin_very_small).toInt()))
}