欢迎您访问程序员文章站本站旨在为大家提供分享程序员计算机编程知识!
您现在的位置是: 首页  >  移动技术

Android RecyclerView更新子项目notifyItemChanged

程序员文章站 2022-05-07 22:07:32
android recyclerview更新子项目notifyitemchanged 在过去android的listview中,如果listview中某一个或者一批项目发生变化,...

android recyclerview更新子项目notifyitemchanged

在过去android的listview中,如果listview中某一个或者一批项目发生变化,需要通过adapter的notifydatasetchanged更新数据到最新,但是从listview演进到现在的recyclerview,数据的更新不需要像listview那样notifydatasetchanged,而是要采用recyclerview的notifyitemchanged,传入一个pos位置,通知recyclerview该pos位置已经失效,需要重新绘制和ui更新。现在给出一个例子,上面一个button按钮,下面一个recyclerview:



    


每次点击button按钮,将随机更新某一个位置的时间到最新:

package zhangphil.demo;

import android.app.activity;
import android.graphics.color;
import android.os.bundle;
import android.support.v7.widget.linearlayoutmanager;
import android.support.v7.widget.recyclerview;
import android.view.layoutinflater;
import android.view.view;
import android.view.viewgroup;
import android.widget.linearlayout;
import android.widget.textview;
import android.widget.toast;

import java.util.arraylist;
import java.util.random;


public class mainactivity extends activity {
    private arraylist data = new arraylist();

    @override
    protected void oncreate(bundle savedinstancestate) {
        super.oncreate(savedinstancestate);
        setcontentview(r.layout.activity_main);

        for (int i = 0; i < 5; i++) {
            data.add(system.currenttimemillis());
        }

        recyclerview mrecyclerview = findviewbyid(r.id.recycler_view);

        linearlayoutmanager mlayoutmanager = new linearlayoutmanager(this);
        mlayoutmanager.setorientation(linearlayout.vertical);
        mrecyclerview.setlayoutmanager(mlayoutmanager);

        final recyclerview.adapter madapter = new myadapter();
        mrecyclerview.setadapter(madapter);

        final random random = new random();

        findviewbyid(r.id.button).setonclicklistener(new view.onclicklistener() {
            @override
            public void onclick(view v) {
                int pos = random.nextint(data.size());
                data.set(pos, system.currenttimemillis());
                madapter.notifyitemchanged(pos);

                toast.maketext(getapplicationcontext(), "更新:" + pos + "," + data.get(pos), toast.length_long).show();
            }
        });
    }


    private class myadapter extends recyclerview.adapter {
        public myadapter() {
            super();
        }

        @override
        public viewholder oncreateviewholder(viewgroup viewgroup, int i) {
            view view = layoutinflater.from(getapplicationcontext()).inflate(android.r.layout.simple_list_item_2, null);
            viewholder holder = new viewholder(view);
            return holder;
        }

        @override
        public void onbindviewholder(viewholder viewholder, int i) {
            viewholder.text1.settext(i + "");
            viewholder.text2.settext(data.get(i) + "");
        }

        @override
        public int getitemcount() {
            return data.size();
        }

        public class viewholder extends recyclerview.viewholder {
            public textview text1;
            public textview text2;

            public viewholder(view itemview) {
                super(itemview);
                text1 = itemview.findviewbyid(android.r.id.text1);
                text1.settextcolor(color.red);
                text2 = itemview.findviewbyid(android.r.id.text2);
                text2.settextcolor(color.blue);
            }
        }
    }
}

事实上recyclerview的notifyitemchanged的底层调用的是notifyitemrangechanged:

 /**
         * notify any registered observers that the item at position has changed.
         * equivalent to calling notifyitemchanged(position, null);.
         *
         * 

this is an item change event, not a structural change event. it indicates that any * reflection of the data at position is out of date and should be updated. * the item at position retains the same identity.

* * @param position position of the item that has changed * * @see #notifyitemrangechanged(int, int) */ public final void notifyitemchanged(int position) { mobservable.notifyitemrangechanged(position, 1); }

该方法使得recyclerview批量范围内(range)数据更新,notifyitemchanged巧妙的将第二个参数计数器设置为1得以实现。后续再介绍recyclerview的notifyitemrangechanged。