通过ItemDecoration来实现类似联系人列表的粘性头部效果，如下图：
效果图
定义实体类
public class GroupItem {
private String content;//item的内容字符串
private boolean isFirst;//是否是该组第一项
private String groupId;//所属组的id
public GroupItem(String content, boolean isFirst, String groupId) {
this.content = content;
this.isFirst = isFirst;
this.groupId = groupId;
}
public String getContent() {
return content;
}
public void setContent(String content) {
this.content = content;
}
public boolean isFirst() {
return isFirst;
}
public void setFirst(boolean first) {
isFirst = first;
}
public String getGroupId() {
return groupId;
}
public void setGroupId(String groupId) {
this.groupId = groupId;
}
}
Deconation的代码如下：
public class HfyDecoration extends RecyclerView.ItemDecoration {
private Paint paint;
private GroupInterface groupInterface;
public HfyDecoration(GroupInterface groupInterface) {
paint = new Paint();
paint.setColor(Color.RED);
paint.setStyle(Paint.Style.FILL);
paint.setAntiAlias(true);
this.groupInterface = groupInterface;
}
@Override
public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
int index = parent.getChildAdapterPosition(view);
if (groupInterface.isFirst(index)) {
//如果是分组第一个，绘制高度为100px的标题
outRect.set(0, 100, 0, 0);
} else {
//普通item，和分组首个的顶部撑开的空间不一样，只绘制5px的分割线
outRect.set(0, 5, 0, 0);
}
}
@Override
public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
super.onDraw(c, parent, state);
int childCount = parent.getChildCount();
for (int i = 0; i < childCount; i++) {
View view = parent.getChildAt(i);
int index = parent.getChildAdapterPosition(view);
if (groupInterface.isFirst(index)) {
//如果是分组第一个，绘制标题
float left = view.getLeft();
float top = view.getTop() - 100;
float bottom = view.getTop();
float right = view.getRight();
paint.setColor(Color.BLUE);
c.drawRect(left, top, right, bottom, paint);
paint.setColor(Color.RED);
paint.setTextSize(100);
c.drawText(groupInterface.getGroupId(index), left, bottom, paint);
} else {
//不是本组第一个，就绘制普通分割线
float left = view.getLeft();
float top = view.getTop() - 5;
float bottom = view.getTop();
float right = view.getRight();
//绘制矩形作为分割线
c.drawRect(left, top, right, bottom, paint);
}
}
}
@Override
public void onDrawOver(Canvas c, RecyclerView parent, RecyclerView.State state) {
super.onDrawOver(c, parent, state);
//绘制顶部标题的坐标
float left = parent.getLeft();
float top = parent.getTop();
float bottom = parent.getTop() + 100;
float right = parent.getRight();
int count = parent.getChildCount();
//当前可见的第一个item
View firstVisibleView = parent.getChildAt(0);
//当前可见的第一个item在数据源中的index
int firstVisbleIndex = parent.getChildAdapterPosition(firstVisibleView);
//当前可见的第一个item的分组id
String firstVisibleGroupId = groupInterface.getGroupId(firstVisbleIndex);
//当前可见的第二个分组的第一个item在RecyclerView的可见位置，默认-1表示可见项没有第二个组
int secondGroupFirstPosition = -1;
//遍历当前可见的第一个之后的所有item（随着滑动，会不断调用，不断遍历实时的新的可见item）
for (int i = 1; i < count; i++) {
View item = parent.getChildAt(i);
int index = parent.getChildAdapterPosition(item);
if (!firstVisibleGroupId.equals(groupInterface.getGroupId(index))) {
//如果和第一个可见item不是同一组，即当前可见的第二组的第一个item
secondGroupFirstPosition = i;
//找到了可见的第二组的第一个item，就停止循环
break;
}
}
//核心思想就是找到可见的第二个组的第一个view，如果这个view距顶部滑动到了两个标题的高度以内，
// 即两个组的标题发生接触，就根据这个view的位置，修改绘制第一组的标题位置
//如果secondGroupFirstPosition是-1，会返回null
View secondGroupFirstView = parent.getChildAt(secondGroupFirstPosition);
if (secondGroupFirstView != null && secondGroupFirstView.getTop() <= 200) {
//第二组的第一个滑动到了特定距离,距顶部两个标题的高度，就开始跟随移动
paint.setColor(Color.BLUE);
//根据第二组的第一个view的top来设置第一组的标题位置，就产生了跟随滑动被顶上去的效果
c.drawRect(left, secondGroupFirstView.getTop() - 200, right, secondGroupFirstView.getTop() - 100, paint);
paint.setColor(Color.RED);
//绘制文字同理
c.drawText(groupInterface.getGroupId(firstVisbleIndex), left, secondGroupFirstView.getTop() - 100, paint);
} else {
//第二组的第一项没有滑到特定距离，或者可见只有一个组，就固定顶部显示第一组的标题id
paint.setColor(Color.BLUE);
c.drawRect(left, top, right, bottom, paint);
paint.setColor(Color.RED);
c.drawText(groupInterface.getGroupId(firstVisbleIndex), left, bottom, paint);
}
}
public interface GroupInterface {
boolean isFirst(int index);
String getGroupId(int index);
}
}
activity的代码如下：
public class MainActivity extends AppCompatActivity {
private RecyclerView recyclerView;
@Override
protected void onCreate(final Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
recyclerView = findViewById(R.id.recycler_view);
recyclerView.setLayoutManager(new LinearLayoutManager(this));
final ArrayList<GroupItem> list = new ArrayList<>();
initData(list);
//实现接口
recyclerView.addItemDecoration(new HfyDecoration(new HfyDecoration.GroupInterface() {
@Override
public boolean isFirst(int index) {
return list.get(index).isFirst();
}
@Override
public String getGroupId(int index) {
return list.get(index).getGroupId();
}
}));
recyclerView.setAdapter(new HfyAdapter(list));
}
private void initData(ArrayList<GroupItem> list) {
list.add(new GroupItem("aa", true, "a"));
list.add(new GroupItem("aaa", false, "a"));
list.add(new GroupItem("aaaa", false, "a"));
list.add(new GroupItem("aaa", false, "a"));
list.add(new GroupItem("bb", true, "b"));
list.add(new GroupItem("bbb", false, "b"));
list.add(new GroupItem("bbbb", false, "b"));
list.add(new GroupItem("bbb", false, "b"));
list.add(new GroupItem("cc", true, "c"));
list.add(new GroupItem("ccc", false, "c"));
list.add(new GroupItem("cccc", false, "c"));
list.add(new GroupItem("ccc", false, "c"));
list.add(new GroupItem("dd", true, "d"));
list.add(new GroupItem("ddd", false, "d"));
list.add(new GroupItem("dddd", false, "d"));
list.add(new GroupItem("ddd", false, "d"));
list.add(new GroupItem("ee", true, "e"));
list.add(new GroupItem("eee", false, "e"));
list.add(new GroupItem("eeee", false, "e"));
list.add(new GroupItem("eee", false, "e"));
list.add(new GroupItem("ff", true, "f"));
list.add(new GroupItem("fff", false, "f"));
list.add(new GroupItem("ffff", false, "f"));
list.add(new GroupItem("fff", false, "f"));
list.add(new GroupItem("fff", false, "f"));
list.add(new GroupItem("fff", false, "f"));
list.add(new GroupItem("fff", false, "f"));
list.add(new GroupItem("fff", false, "f"));
list.add(new GroupItem("fff", false, "f"));
list.add(new GroupItem("fff", false, "f"));
list.add(new GroupItem("fff", false, "f"));
list.add(new GroupItem("fff", false, "f"));
list.add(new GroupItem("fff", false, "f"));
list.add(new GroupItem("fff", false, "f"));
list.add(new GroupItem("fff", false, "f"));
}
}
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