分割线
分割线在app中是经常用到的,用ItemDecoration怎么实现呢,其实上面padding改成1dp就实现了分割线的效果,但是分割线的颜色只能是背景灰色,所以不能用这种方法。
要实现分割线效果需要 getItemOffsets()和 onDraw()2个方法,首先用 getItemOffsets给item下方空出一定高度的空间(例子中是1dp),然后用onDraw绘制这个空间
//分割线
public class DividerItemDecoration extends RecyclerView.ItemDecoration {
private Context mContext; //上下文
private int dividerHeight; //分割线的高度
private Paint mPaint; //画笔
//自定义构造方法,在构造方法中初始化一些变量
public DividerItemDecoration(Context context){
mContext = context;
dividerHeight = 2; //context.getResources().getDimensionPixelSize(R.dimen.divider_height);
mPaint = new Paint();
mPaint.setColor(context.getResources().getColor(R.color.colorAccent)); //设置颜色
}
//设置padding
@Override
public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
super.getItemOffsets(outRect, view, parent, state);
//outRect.bottom、left,right,top设置为int值,设置每一项的padding
outRect.bottom =dividerHeight ;
}
//画图
@Override
public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
super.onDraw(c, parent, state);
//获取item个数
int childCount = parent.getChildCount();
//左右是固定的
int left = parent.getPaddingLeft();
int right = parent.getWidth() - parent.getPaddingRight() ;
//高度
for (int i = 0; i < childCount - 1; i++) {
View view = parent.getChildAt(i);
float top = view.getBottom();
float bottom = view.getBottom() + dividerHeight;
//画图
c.drawRect(left, top, right, bottom, mPaint);
}
}
}
效果如下:
现在很多电商app会给商品加上一个标签,比如“推荐”,“热卖”,“秒杀”等等,可以看到这些标签都是覆盖在内容之上的,这就可以用onDrawOver()来实现,我们这里简单实现一个有趣的标签
public class LeftAndRightTagDecoration extends RecyclerView.ItemDecoration {
private int tagWidth; //标签的宽度
private Paint leftPaint; //左边的画笔
private Paint rightPaint; //右边的画笔
public LeftAndRightTagDecoration(Context context){
leftPaint =new Paint();
leftPaint.setColor(context.getResources().getColor(R.color.colorPrimary));
rightPaint = new Paint();
rightPaint.setColor(context.getResources().getColor(R.color.colorOrange));
//上面是画笔的初始化,和设置颜色,下面是标签宽度的获取
tagWidth = context.getResources().getDimensionPixelSize(R.dimen.tag_width);
}
//绘制标签
@Override
public void onDrawOver(Canvas c, RecyclerView parent, RecyclerView.State state) {
super.onDrawOver(c, parent, state);
int childCount = parent.getChildCount();
for(int i=0;i<childCount;i++){
View child = parent.getChildAt(i);
int pos = parent.getChildAdapterPosition(child);
boolean isLeft = pos%2==0;
if(isLeft){
float left = child.getLeft();
float right = left+tagWidth;
float top = child.getTop();
float bottom =child.getBottom();
c.drawRect(left,top,right,bottom,leftPaint);
}else{
float right = child.getRight();
float left = right-tagWidth;
float top = child.getTop();
float bottom =child.getBottom();
c.drawRect(left,top,right,bottom,rightPaint);
}
}
}
}
section
这个是什么呢,先看下我们实现的效果
一看这个就很熟悉吧,手机上面的通讯录联系人,知乎日报都是这样效果,可以叫分组,也可以叫section分块 先不管它叫什么。
这个怎么实现呢? 其实和实现分割线是一样的道理 ,只是不是所有的item都需要分割线,只有同组的第一个需要。
我们首先定义一个接口给activity进行回调用来进行数据分组和获取首字母
public interface DecorationCallback {
long getGroupId(int position);
String getGroupFirstLine(int position);
}
然后再来看我们的ItemDecoration
public class SectionDecoration extends RecyclerView.ItemDecoration {
private DecorationCallback callback;
private TextPaint textPaint; //文字画笔
private Paint paint; //普通画笔
private int topGap; //padding_top
private Paint.FontMetrics fontMetrics;
//自定义构造函数
public SectionDecoration(Context context, DecorationCallback decorationCallback) {
Resources res = context.getResources();
this.callback = decorationCallback;
//画笔
paint = new Paint();
paint.setColor(res.getColor(R.color.colorPrimary));
//文字画笔,样式设置
textPaint = new TextPaint();
textPaint.setTypeface(Typeface.DEFAULT_BOLD); //加粗
textPaint.setAntiAlias(true);
textPaint.setTextSize(70); //字体大小
textPaint.setColor(Color.BLACK); //字体颜色
textPaint.getFontMetrics(fontMetrics); //字体的材质
textPaint.setTextAlign(Paint.Align.LEFT); //字体的向左对齐
fontMetrics = new Paint.FontMetrics();
topGap = res.getDimensionPixelSize(R.dimen.sectioned_top);//32dp Padding——top的值
}
@Override
public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
super.getItemOffsets(outRect, view, parent, state);
//视图的位置
int pos = parent.getChildAdapterPosition(view);
long groupId = callback.getGroupId(pos);
if (groupId < 0) return;
if (pos == 0 || isFirstInGroup(pos)) {//同组的第一个才添加padding
outRect.top = topGap;
} else {
outRect.top = 0;
}
}
@Override
public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
super.onDraw(c, parent, state);
int left = parent.getPaddingLeft();
int right = parent.getWidth() - parent.getPaddingRight();
int childCount = parent.getChildCount();
for (int i = 0; i < childCount; i++) {
View view = parent.getChildAt(i);
int position = parent.getChildAdapterPosition(view);
long groupId = callback.getGroupId(position);
if (groupId < 0) return;
//分组的文本
String textLine = callback.getGroupFirstLine(position).toUpperCase();
if (position == 0 || isFirstInGroup(position)) {
float top = view.getTop() - topGap;
float bottom = view.getTop();
c.drawRect(left, top, right, bottom, paint);//绘制矩形
c.drawText(textLine, left, bottom, textPaint);//绘制文本
}
}
}
//是否是一个组
private boolean isFirstInGroup(int pos) {
if (pos == 0) {
return true;
} else {
long prevGroupId = callback.getGroupId(pos - 1);
long groupId = callback.getGroupId(pos);
return prevGroupId != groupId;
}
}
//接口实现分组的依据
public interface DecorationCallback {
long getGroupId(int position);
String getGroupFirstLine(int position);
}
}
可以看到和divider实现一样,都是重写getItemOffsets()和onDraw()2个方法,不同的是根据数据做了处理。
在Activity中使用
mRecycleView.addItemDecoration(new SectionDecoration(this, new SectionDecoration.DecorationCallback() {
@Override
public long getGroupId(int position) {
return Character.toUpperCase(homeAdapter.mTitles[position].charAt(0));
}
@Override
public String getGroupFirstLine(int position) {
return homeAdapter.mTitles[position].substring(0, 1).toUpperCase();
}
}));
干净舒服,不少github类似的库都是去adapter进行处理 侵入性太强 或许ItemDecoration是个更好的选择,可插拔,可替换。
到这里细心的人就会发现了,header不会动啊,我手机上的通讯录可是会随的滑动而变动呢,这个可以实现么?
StickyHeader
这个东西怎么叫我也不知道啊 粘性头部?英文也有叫 pinned section 取名字真是个麻烦事。
先看下我们简单实现的效果
首先一看到图,我们就应该想到header不动肯定是要绘制item内容之上的,需要重写onDrawOver()方法,其他地方和section实现一样。
public class PinnedSectionDecoration extends RecyclerView.ItemDecoration {
private static final String TAG = "PinnedSectionDecoration";
private DecorationCallback callback;
private TextPaint textPaint;
private Paint paint;
private int topGap;
private Paint.FontMetrics fontMetrics;
public PinnedSectionDecoration(Context context, DecorationCallback decorationCallback) {
Resources res = context.getResources();
this.callback = decorationCallback;
paint = new Paint();
paint.setColor(res.getColor(R.color.colorAccent));
textPaint = new TextPaint();
textPaint.setTypeface(Typeface.DEFAULT_BOLD);
textPaint.setAntiAlias(true);
textPaint.setTextSize(80);
textPaint.setColor(Color.BLACK);
textPaint.getFontMetrics(fontMetrics);
textPaint.setTextAlign(Paint.Align.LEFT);
fontMetrics = new Paint.FontMetrics();
topGap = res.getDimensionPixelSize(R.dimen.sectioned_top);
}
@Override
public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
super.getItemOffsets(outRect, view, parent, state);
int pos = parent.getChildAdapterPosition(view);
long groupId = callback.getGroupId(pos);
if (groupId < 0) return;
if (pos == 0 || isFirstInGroup(pos)) {
outRect.top = topGap;
} else {
outRect.top = 0;
}
}
@Override
public void onDrawOver(Canvas c, RecyclerView parent, RecyclerView.State state) {
super.onDrawOver(c, parent, state);
int itemCount = state.getItemCount();
int childCount = parent.getChildCount();
int left = parent.getPaddingLeft();
int right = parent.getWidth() - parent.getPaddingRight();
float lineHeight = textPaint.getTextSize() + fontMetrics.descent;
long preGroupId, groupId = -1;
for (int i = 0; i < childCount; i++) {
View view = parent.getChildAt(i);
int position = parent.getChildAdapterPosition(view);
preGroupId = groupId;
groupId = callback.getGroupId(position);
if (groupId < 0 || groupId == preGroupId) continue;
String textLine = callback.getGroupFirstLine(position).toUpperCase();
if (TextUtils.isEmpty(textLine)) continue;
int viewBottom = view.getBottom();
float textY = Math.max(topGap, view.getTop());
if (position + 1 < itemCount) { //下一个和当前不一样移动当前
long nextGroupId = callback.getGroupId(position + 1);
if (nextGroupId != groupId && viewBottom < textY ) {//组内最后一个view进入了header
textY = viewBottom;
}
}
c.drawRect(left, textY - topGap, right, textY, paint);
c.drawText(textLine, left, textY, textPaint);
}
}
}
好了,现在发现ItemDecoration有多强大了吧! 当然还有更多就需要你自己去发现了。