思路和代码，从张旭童同学的使用ItemDecoration为RecyclerView打造带悬停头部的分组列表学来的
运行效果
1. TitleItemDecoration <p>
public class TitleItemDecoration extends RecyclerView.ItemDecoration {
private Rect textBound;//文字的范围i
private Paint mPaint;
private List<ResourceBean> subjectList = new ArrayList<>();
private int mTitleHeight;//title的高
private final int COLOR_BG = Color.parseColor("#303F9F");
private final int COLOR_FONT = Color.WHITE;
private final int decoration;
public TitleItemDecoration(Context context, List<ResourceBean> subjectList,int decoration) {
this.decoration = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, decoration, context.getResources().getDisplayMetrics());
this.subjectList.clear();
this.subjectList.addAll(subjectList);
mTitleHeight = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 30, context.getResources().getDisplayMetrics());
//title字体大小
final float mFontSize = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_SP, 16, context.getResources().getDisplayMetrics());
textBound = new Rect();
mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
mPaint.setTextSize(mFontSize);
}
/**
* 设置Title的空间
*/
@Override
public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
super.getItemOffsets(outRect, view, parent, state);
int position = parent.getChildLayoutPosition(view);
if (position == 0) {//position为0，第一个item有title
outRect.set(0, mTitleHeight, 0, decoration);//留下title空间
} else {//对是否需要留白 进行判断
ResourceBean resourceBean = subjectList.get(position);
ResourceBean lastBean = subjectList.get(position - 1);
if (resourceBean == null || lastBean == null) return;
if (!resourceBean.getSubject().equals(lastBean.getSubject())) {//和上一个的科目不一样
outRect.set(0, mTitleHeight, 0, decoration);//留下title空间
} else {
outRect.set(0, 0, 0, decoration);
}
}
}
/**
* 绘制Title
*/
@Override
public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
super.onDraw(c, parent, state);
final int left = parent.getPaddingLeft();
final int right = parent.getWidth() - parent.getPaddingRight();
final int current = parent.getChildCount();//屏幕当前item数量
for (int i = 0; i < current; i++) {
final View child = parent.getChildAt(i);//获取childView
RecyclerView.LayoutParams layoutParams = (RecyclerView.LayoutParams) child.getLayoutParams();
int position = parent.getChildLayoutPosition(child);//child的adapter position
if (position == 0) {//为0 绘制title
ResourceBean resourceBean = subjectList.get(position);
if (resourceBean == null) return;
String title = resourceBean.getSubject();
drawTitle(c, left, right, child, layoutParams, title);//进行绘制
} else {//不为0时 判断 是否需要绘制title
ResourceBean resourceBean = subjectList.get(position);
ResourceBean lastBean = subjectList.get(position - 1);
if (resourceBean == null || lastBean == null) return;
if (!resourceBean.getSubject().equals(lastBean.getSubject())) {//和上一个的科目不一样
drawTitle(c, left, right, child, layoutParams, resourceBean.getSubject());
}
}
}
}
/**
* 绘制文字
*/
private void drawTitle(Canvas c, int left, int right, View child, RecyclerView.LayoutParams layoutParams, String titleText) {
//绘制背景色
mPaint.setColor(COLOR_BG);
c.drawRect(left, child.getTop() - layoutParams.topMargin - mTitleHeight, right, child.getTop() - layoutParams.topMargin, mPaint);
//绘制文字，没有使用计算baseline的方式
mPaint.setColor(COLOR_FONT);
mPaint.getTextBounds(titleText, 0, titleText.length(), textBound);
c.drawText(titleText, child.getPaddingLeft(), child.getTop() - layoutParams.topMargin - (mTitleHeight / 2 - textBound.height() / 2), mPaint);
}
/**
* 绘制蒙层
*/
@Override
public void onDrawOver(Canvas c, RecyclerView parent, RecyclerView.State state) {
super.onDrawOver(c, parent, state);
final LinearLayoutManager manager = (LinearLayoutManager) parent.getLayoutManager();
final int firstPosition = manager.findFirstVisibleItemPosition();
final ResourceBean resourceBean = subjectList.get(firstPosition);
if (resourceBean == null) return;
final String subject = subjectList.get(firstPosition).getSubject();
final View child = parent.findViewHolderForAdapterPosition(firstPosition).itemView;
final ResourceBean secondBean = subjectList.get(firstPosition + 1);
boolean flag = false;
if (!subject.equals(secondBean.getSubject())) {
if (child.getHeight() + child.getTop() < mTitleHeight) {//两个tile开始接触，第一item在屏幕剩余的高度小于title高度
c.save();
c.translate(0, child.getHeight() + child.getTop() - mTitleHeight+decoration);//将画布向上平移
flag = true;
}
}
mPaint.setColor(COLOR_BG);
c.drawRect(0, parent.getPaddingTop(), parent.getRight() - parent.getPaddingRight(), parent.getPaddingTop() + mTitleHeight, mPaint);
mPaint.setColor(COLOR_FONT);
mPaint.getTextBounds(subject, 0, subject.length(), textBound);
c.drawText(subject, child.getPaddingLeft(), mTitleHeight - (mTitleHeight / 2 - textBound.height() / 2), mPaint);
if (flag)c.restore();
}
}
2. Activity代码
public class ResourceActivity extends AppCompatActivity {
private RecyclerView rv;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_resouce);
init();
}
private void init() {
rv = (RecyclerView) findViewById(R.id.rv_resource_activity);
//布局管理器
//GridLayoutManager manager = new GridLayoutManager(this, 2);
LinearLayoutManager manager = new LinearLayoutManager(this);
manager.setOrientation(GridLayoutManager.VERTICAL);
rv.setLayoutManager(manager);
//适配器
ResourceAdapter adapter = new ResourceAdapter(rv, R.layout.id_rv_item_layout);
rv.setAdapter(adapter);
addData(adapter,rv);
}
/**
* 添加数据
*/
private void addData(ResourceAdapter adapter,RecyclerView rv) {
final List<ResourceBean> listData = new ArrayList<>();
for (int i = 0 ; i < 15; i ++){
int num = (int)(Math.random() * 7+1);
for (int j = 0 ; j < num ; j ++){
ResourceBean resourceBean= new ResourceBean();
resourceBean.setSubject("学科"+i);
resourceBean.setName("资料"+j);
listData.add(resourceBean);
}
}
adapter.setData(listData);
//添加ItemDecoration
rv.addItemDecoration(new TitleItemDecoration(ResourceActivity.this,listData,2));
}
@Override
protected void onDestroy() {
super.onDestroy();
if (null != rv) rv.setAdapter(null);
}
}
搭配LineraLayoutManager比较方便实现。当我想配合GridLayoutManager也使用这种方式时，遇到了问题，item和title是一体的，使用ItemDecoration设置的title，想不出使用什么办法来占据单独的一行
2016.10.19 18:38
