RecyclerView超级简单的实现吸顶效果

不会自定义View的厨子,写不出好代码!

首先,说说需求:

1.列表自定义分组;

2.分组类标标题实现吸顶效果;

先上效果图:


其实就是自定义一个 RecyclerView.ItemDecoration,自己实现分割线,分组标签也是分割线来实现的:上代码



package com.example.recylerviewdemo;

import android.content.Context;

import android.graphics.Canvas;

import android.graphics.Color;

import android.graphics.Paint;

import android.graphics.Rect;

import android.text.TextPaint;

import android.view.View;

import androidx.annotation.NonNull;

import androidx.recyclerview.widget.LinearLayoutManager;

import androidx.recyclerview.widget.RecyclerView;

/**

*

*/

class StarItemDecrationextends RecyclerView.ItemDecoration {

private int HEAD_HEIGHT ;

    private PaintmPaint;

    private PainttextPaint;

    private RecttextRect;

    public StarItemDecration(Context context) {

HEAD_HEIGHT = dp2px(context,120);

        mPaint =new Paint();

        mPaint.setColor(Color.RED);

        textPaint =new TextPaint();

        textPaint.setTextSize(50);

        textPaint.setColor(Color.BLACK);

        textRect =new Rect();

    }

@Override

    public void onDraw(@NonNull Canvas canvas, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {

super.onDraw(canvas, parent, state);

        if(parent.getAdapter()instanceof StartAdapter) {

StartAdapter startAdapter = (StartAdapter) parent.getAdapter();

            int childCount = parent.getChildCount();

            int left = parent.getPaddingLeft();

            int right = parent.getWidth() - parent.getPaddingRight();

            for (int i =0; i < childCount; i++) {

View view = parent.getChildAt(i);

                int positon = parent.getChildLayoutPosition(view);

                boolean isHead = startAdapter.isGroupHeader(positon);

                if(isHead && view.getTop() -HEAD_HEIGHT -parent.getPaddingTop() >=0) {

canvas.drawRect(left,view.getTop() -HEAD_HEIGHT,right,view.getTop(),mPaint);

                    String groupName = startAdapter.getGroupName(positon);

                    textPaint.getTextBounds(groupName,0,groupName.length(),textRect);

                    canvas.drawText(groupName,left +20,view.getTop() -HEAD_HEIGHT/2 +textRect.height()/2,textPaint);

                }else if(view.getTop() -HEAD_HEIGHT -parent.getPaddingTop() >=0){

canvas.drawRect(left,view.getTop() -3,right,view.getTop(),mPaint);

                }

}

}

}

@Override

    public void onDrawOver(@NonNull Canvas c, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {

super.onDrawOver(c, parent, state);

        if(parent.getAdapter()instanceof StartAdapter) {

StartAdapter startAdapter = (StartAdapter) parent.getAdapter();

            int position = ((LinearLayoutManager) parent.getLayoutManager()).findFirstVisibleItemPosition();

            View itemView = parent.findViewHolderForAdapterPosition(position).itemView;

            int left = parent.getLeft();

            int right = parent.getWidth() - parent.getPaddingRight();

            int top = parent.getPaddingTop();

            String groupName = startAdapter.getGroupName(position );

            if(startAdapter.isGroupHeader(position +1)){

int bottom = Math.min(HEAD_HEIGHT,itemView.getBottom() - top);

                c.drawRect(left,top,right,top + bottom,mPaint);

                textPaint.getTextBounds(groupName,0,groupName.length(),textRect);

                c.drawText(groupName,left +20,itemView.getTop() +HEAD_HEIGHT/2 +textRect.height()/2,textPaint);

            }else{

c.drawRect(left,top,right,top +HEAD_HEIGHT,mPaint);

                textPaint.getTextBounds(groupName,0,groupName.length(),textRect);

                c.drawText(groupName,left +20,top +HEAD_HEIGHT/2 +textRect.height()/2,textPaint);

            }

}

}

@Override

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

super.getItemOffsets(outRect, view, parent, state);

        if(parent.getAdapter()instanceof StartAdapter) {

StartAdapter startAdapter = (StartAdapter) parent.getAdapter();

            int positon = parent.getChildLayoutPosition(view);

            if(startAdapter.isGroupHeader(positon)){

outRect.set(0, HEAD_HEIGHT, 0, 0);

            }else{

outRect.set(0, 3, 0, 0);

            }

}

}

private int dp2px(Context context, float dp){

float scale = context.getResources().getDisplayMetrics().density;

        return (int) (dp * scale *0.5f);

    }

}

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