概述:
當我們準備爲RecyclerView添加分割線時,你會發現RecyclerView並沒有支持divider這樣的屬性。想想辦法,你可以給Item的佈局去設置margin,當然了這種方式不夠優雅,我們可以自由的去定製它。
繪製橫向或縱向列表分割線:
RecyclerView.ItemDecoration是一個抽象類,就是用來裝飾RecyclerView的子item的,通過名字就可以知道,功能並不僅僅是添加間距繪製分割線,是用來裝飾item的。
這個類包含三個方法 :
1、getItemOffsets(Rect outRect, View view, RecyclerView parent, State state)//設置四邊邊距
2、onDraw(Canvas c, RecyclerView parent, State state)//繪製裝飾
3、onDrawOver(Canvas c, RecyclerView parent, State state)//繪製蒙層
1、getItemOffsets(Rect outRect, View view, RecyclerView parent, State state)方法:
該方法中有4個參數:
1、Rect outRect: outRect 設置的4個方向的值,將被計算進所有 decoration 的尺寸中,而這個尺寸,被用來計算 RecyclerView 每個 item view 的padding間距大小。
2、View view: childView,就是item,可以理解爲item的根View,並不是item中的控件
3、RecyclerView parent:就是RecyclerView自身
4、RecyclerView.State state : RecyclerView的狀態
代碼實現:
//獲取分割線尺寸
@Override
public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
super.getItemOffsets(outRect, view, parent, state);
outRect.set(0, 0, 0, mDividerHeight);
}
2、onDraw(Canvas c, RecyclerView parent, RecyclerView.State state)方法:
onDraw用於繪製divider,繪製到每一個item的下一層,也就是說item會蓋在divider所在層的上面
onDraw()方法可以爲divier設置繪製範圍,並且繪製範圍可以超出在 getItemOffsets中設置的範圍,但由於是在item下面一層進行繪製,會存在overdraw
代碼實現:
//繪製分割線
@Override
public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
super.onDraw(c, parent, state);
if (mOrientation == LinearLayoutManager.VERTICAL) {
drawVertical(c, parent);
} else {
drawHorizontal(c, parent);
}
}
//繪製橫向 item 分割線
private void drawHorizontal(Canvas canvas, RecyclerView parent) {
final int left = parent.getPaddingLeft();
final int right = parent.getMeasuredWidth() - parent.getPaddingRight();
final int childSize = parent.getChildCount();
for (int i = 0; i < childSize; i++) {
final View child = parent.getChildAt(i);
RecyclerView.LayoutParams layoutParams = (RecyclerView.LayoutParams) child.getLayoutParams();
final int top = child.getBottom() + layoutParams.bottomMargin;
final int bottom = top + mDividerHeight;
if (mDivider != null) {
mDivider.setBounds(left, top, right, bottom);
mDivider.draw(canvas);
}
if (mPaint != null) {
canvas.drawRect(left, top, right, bottom, mPaint);
}
}
}
//繪製縱向 item 分割線
private void drawVertical(Canvas canvas, RecyclerView parent) {
final int top = parent.getPaddingTop();
final int bottom = parent.getMeasuredHeight() - parent.getPaddingBottom();
final int childSize = parent.getChildCount();
for (int i = 0; i < childSize; i++) {
final View child = parent.getChildAt(i);
RecyclerView.LayoutParams layoutParams = (RecyclerView.LayoutParams) child.getLayoutParams();
final int left = child.getRight() + layoutParams.rightMargin;
final int right = left + mDividerHeight;
if (mDivider != null) {
mDivider.setBounds(left, top, right, bottom);
mDivider.draw(canvas);
}
if (mPaint != null) {
canvas.drawRect(left, top, right, bottom, mPaint);
}
}
}
3、onDrawOver(Canvas c, RecyclerView parent, RecyclerView.State state)方法:
這個方法是在item的onDraw()方法之後進行回調,也就繪製在了最上層
由於 onDrawOver 是繪製在最上層的,所以它的繪製位置並不受限制,
只要手指在RecyclerView上進行滑動,onDrawOver()方法就會被回調。但onDrawOver()每回調一次,會將上次的繪製清除,只有最後一次的繪製會被保留。也就是說繪製的蒙層在屏幕只會有一個
所以利用 onDrawOver 可以做很多事情,例如爲 RecyclerView 整體頂部繪製一個蒙層,或者爲特定的 item view 繪製蒙層。這裏就不單獨進行測試了。
繪製九宮格佈局樣式分割線:
對於分割線,前面的DividerItemDecoration就不適用了,主要是因爲它在繪製的時候,比如水平線,因爲每個Item一行,這樣是沒問題的。而GridLayoutManager時,一行有多個childItem,這樣就多次繪製了,並且GridLayoutManager時,Item如果爲最後一列(則右邊無間隔線)或者爲最後一行(底部無分割線)。
主要在getItemOffsets方法中,去判斷如果是最後一行,則不需要繪製底部;如果是最後一列,則不需要繪製右邊,整個判斷也考慮到了StaggeredGridLayoutManager的橫向和縱向,所以稍稍有些複雜
1、getItemOffsets(Rect outRect, View view, RecyclerView parent, State state)方法:
@Override
@Deprecated
public void getItemOffsets(Rect outRect, int itemPosition,
RecyclerView parent) {
// 四個方向的偏移值
int right = mDivider.getIntrinsicWidth();
int bottom = mDivider.getIntrinsicHeight();
if(isLastColum(itemPosition,parent)){//是否是最後一列
// outRect.set(0, 0, 0, bottom);
right = 0;
}
if(isLastRow(itemPosition,parent)){//是最後一行
// outRect.set(0, 0, right, 0);
bottom = 0;
}
outRect.set(0, 0, right, bottom);
}
/**
* 是否是最後一行
* @param itemPosition
* @param parent
* @return
*/
private boolean isLastRow(int itemPosition, RecyclerView parent) {
int spanCount = getSpanCount(parent);
LayoutManager layoutManager = parent.getLayoutManager();
//有多少列
if(layoutManager instanceof GridLayoutManager){
int childCount = parent.getAdapter().getItemCount();
int lastRowCount = childCount%spanCount;
//最後一行的數量小於spanCount
if(lastRowCount==0||lastRowCount<spanCount){
return true;
}
}
return false;
}
/**
* 判斷是否是最後一列
* @param itemPosition
* @param parent
* @return
*/
private boolean isLastColum(int itemPosition, RecyclerView parent) {
LayoutManager layoutManager = parent.getLayoutManager();
//有多少列
if(layoutManager instanceof GridLayoutManager){
int spanCount = getSpanCount(parent);
if((itemPosition+1)%spanCount==0){
return true;
}
}
return false;
}
2、onDraw(Canvas c, RecyclerView parent, RecyclerView.State state)方法:
@Override
public void onDraw(Canvas c, RecyclerView parent, State state) {
drawVertical(c,parent);
drawHorizontal(c,parent);
}
private void drawHorizontal(Canvas c, RecyclerView parent) {
// 繪製水平間隔線
int childCount = parent.getChildCount();
for (int i = 0; i < childCount; i++) {
View child = parent.getChildAt(i);
RecyclerView.LayoutParams params = (LayoutParams) child.getLayoutParams();
int left = child.getLeft() - params.leftMargin;
int right = child.getRight()+ params.rightMargin;
int top = child.getBottom() + params.bottomMargin;
int bottom = top + mDivider.getIntrinsicHeight();
mDivider.setBounds(left, top, right, bottom);
mDivider.draw(c);
}
}
private void drawVertical(Canvas c, RecyclerView parent) {
//繪製垂直間隔線(垂直的矩形)
int childCount = parent.getChildCount();
for (int i = 0; i < childCount; i++) {
View child = parent.getChildAt(i);
RecyclerView.LayoutParams params = (LayoutParams) child.getLayoutParams();
int left = child.getRight() + params.rightMargin;
int right = left + mDivider.getIntrinsicWidth();
int top = child.getTop() - params.topMargin;
int bottom = child.getBottom() + params.bottomMargin;
mDivider.setBounds(left, top, right, bottom);
mDivider.draw(c);
}
}
源碼demo鏈接:
https://github.com/heiyl/recyleview