问RecyclerView粘性标题

EN

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;

import com.example.evaluationtask.Model.StateModel;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import java.io.IOException;
import java.io.InputStream;
import java.nio.charset.StandardCharsets;
import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {

    RecyclerView recyclerView;
    RecyclerView.LayoutManager layoutManager;
    ViewAdapter viewAdapter;
    List<StateModel> list;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        recyclerView = findViewById(R.id.recyclerView);
        recyclerView.setHasFixedSize(true);
        layoutManager = new LinearLayoutManager(this);
        recyclerView.setLayoutManager(layoutManager);

        list = new ArrayList<>();
        loadJSONFromAsset();

        viewAdapter = new ViewAdapter(list);

        System.out.println("List Items : " + list);
        recyclerView.setAdapter(viewAdapter);

        RecyclerSectionItemDecoration sectionItemDecoration = new RecyclerSectionItemDecoration(getResources()
                .getDimensionPixelSize(R.dimen.header),
                true,
                getSectionCallback(list));
        recyclerView.addItemDecoration(sectionItemDecoration);
        viewAdapter.notifyDataSetChanged();


    }

    public void loadJSONFromAsset() {
        String json;

        try {

            InputStream inputStream = getAssets().open("StateAlert.json");
            int size = inputStream.available();
            byte[] buffer = new byte[size];
            inputStream.read(buffer);
            inputStream.close();
            json = new String(buffer, StandardCharsets.UTF_8);
            JSONArray jsonElements = new JSONArray(json);

            for (int i = 0; i < jsonElements.length(); i++) {

                JSONObject jsonObject = jsonElements.getJSONObject(i);
                StateModel stateModel = new StateModel();
                stateModel.setId(jsonObject.optInt("id", 0));
                stateModel.setCreated(jsonObject.optString("Created", "N/A"));
                stateModel.setDescription(jsonObject.optString("Description", "N/A"));
                stateModel.setHistoryCount(jsonObject.optInt("HistoryCount", 0));
                stateModel.setStatus(jsonObject.optString("Status", "N/A"));
                stateModel.setType(jsonObject.optString("Type", "N/A"));
                list.add(stateModel);

            }

        } catch (IOException e) {

            e.printStackTrace();
        } catch (JSONException e) {

            e.printStackTrace();
        }
    }

    private RecyclerSectionItemDecoration.SectionCallback getSectionCallback(final List<StateModel> stateModels) {
        return new RecyclerSectionItemDecoration.SectionCallback() {
            @Override
            public boolean isSection(int position) {
                return true;
            }

            @Override
            public CharSequence getSectionHeader(int position) {
                return stateModels.get(position)
                        .getType();
            }
        };
    }
}

import android.graphics.Canvas;
import android.graphics.Rect;
import android.support.annotation.NonNull;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

class RecyclerSectionItemDecoration extends RecyclerView.ItemDecoration {

    private final int headerOffset;
    private final boolean sticky;
    private final SectionCallback sectionCallback;

    private View headerView;
    private TextView header;

    public RecyclerSectionItemDecoration(int headerHeight, boolean sticky, @NonNull SectionCallback sectionCallback) {
        headerOffset = headerHeight;
        this.sticky = sticky;
        this.sectionCallback = sectionCallback;
    }

    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
        super.getItemOffsets(outRect, view, parent, state);

        int pos = parent.getChildAdapterPosition(view);
        if (sectionCallback.isSection(pos)) {
            outRect.top = headerOffset;
        }
    }

    @Override
    public void onDrawOver(Canvas c, RecyclerView parent, RecyclerView.State state) {
        super.onDrawOver(c, parent, state);

        if (headerView == null) {
            headerView = inflateHeaderView(parent);
            header = headerView.findViewById(R.id.tv_header);
            fixLayoutSize(headerView, parent);
        }

        CharSequence previousHeader = "";
        for (int i = 0; i < parent.getChildCount(); i++) {
            View child = parent.getChildAt(i);
            final int position = parent.getChildAdapterPosition(child);

            CharSequence title = sectionCallback.getSectionHeader(position);
            header.setText(title);
            if (!previousHeader.equals(title) || sectionCallback.isSection(position)) {
                drawHeader(c, child, headerView);
                previousHeader = title;
            }
        }
    }

    private void drawHeader(Canvas c, View child, View headerView) {
        c.save();
        if (sticky) {
            c.translate(0, Math.max(0, child.getTop() - headerView.getHeight()));
        } else {
            c.translate(0, child.getTop() - headerView.getHeight());
        }
        headerView.draw(c);
        c.restore();
    }

    private View inflateHeaderView(RecyclerView parent) {
        return LayoutInflater.from(parent.getContext())
                .inflate(R.layout.view_header, parent, false);
    }

    private void fixLayoutSize(View view, ViewGroup parent) {
        int widthSpec = View.MeasureSpec.makeMeasureSpec(parent.getWidth(),
                View.MeasureSpec.EXACTLY);
        int heightSpec = View.MeasureSpec.makeMeasureSpec(parent.getHeight(),
                View.MeasureSpec.UNSPECIFIED);

        int childWidth = ViewGroup.getChildMeasureSpec(widthSpec,
                parent.getPaddingLeft() + parent.getPaddingRight(),
                view.getLayoutParams().width);
        int childHeight = ViewGroup.getChildMeasureSpec(heightSpec,
                parent.getPaddingTop() + parent.getPaddingBottom(),
                view.getLayoutParams().height);

        view.measure(childWidth, childHeight);

        view.layout(0, 0, view.getMeasuredWidth(), view.getMeasuredHeight());
    }

    public interface SectionCallback {

        boolean isSection(int position);

        CharSequence getSectionHeader(int position);
    }


}

import android.support.annotation.NonNull;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.TextView;

import com.example.evaluationtask.Model.StateModel;

import java.util.List;

public class ViewAdapter extends RecyclerView.Adapter<ViewAdapter.ItemViewHolder> {

    List<StateModel> dataSet;

    @NonNull
    @Override
    public ItemViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) {
        View view = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.item_list_view, viewGroup, false);
        return new ItemViewHolder(view);
    }

    @Override
    public void onBindViewHolder(@NonNull ItemViewHolder itemViewHolder, int i) {
        itemViewHolder.button.setText(dataSet.get(i).getStatus());
        itemViewHolder.shoreTitle.setText(dataSet.get(i).getDescription());
        itemViewHolder.createdAt.setText(dataSet.get(i).getCreated());

    }

    @Override
    public int getItemCount() {
        return dataSet.size();
    }

    public static class ItemViewHolder extends RecyclerView.ViewHolder {
        public TextView shoreTitle;
        public TextView createdAt;
        public Button button;

        public ItemViewHolder(@NonNull View itemView) {
            super(itemView);
            this.createdAt = itemView.findViewById(R.id.createdAt);
            this.shoreTitle = itemView.findViewById(R.id.shore_text);
            this.button = itemView.findViewById(R.id.btn_card);
        }
    }

    public ViewAdapter(List<StateModel> dataSet) {
        this.dataSet = dataSet;
    }
}