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Android RecyclerView更新子项目notifyItemChanged

2019年04月18日  | 移动技术网IT编程  | 我要评论

陈桥兵变令人疑,2016湖南高考状元,摩纳哥夏洛特公主

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。

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