Android学习笔记之PullToRefreshListView和BaseAdapter的使用

　　下拉刷新是很多应用都使用的很流行的一种效果，今天也算是彻底的理解了一下PullToRefreshListView的使用，但是弄了一天却在一个很傻的地方犯了错误。

  @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ViewHolder holder;
        if (convertView == null) {
            convertView = LayoutInflater.from(context).inflate(R.layout.news_items, null);
            holder = new ViewHolder();
            holder.newsImage = (ImageView) convertView.findViewById(R.id.news_image);
            holder.titleTextView = (TextView) convertView.findViewById(R.id.news_title);
            convertView.setTag(holder);
        }else {
            holder = (ViewHolder) convertView.getTag();
        }

        News news = newses.get(position);
        if (news != null) {

            holder.titleTextView.setText(newses.get(position).getTitle());

            AVFile avFile = newses.get(position).getAVFile("image");
            if (avFile == null) {
                Logger.d("该条新闻的图片没有");

            }
            if (avFile != null) {
                String url = avFile.getUrl();
                //显示图片的配置
                DisplayImageOptions options = new DisplayImageOptions.Builder()
                        .showImageOnFail(R.drawable.healthy_icon01)
                        .showImageForEmptyUri(R.drawable.healthy_icon01)
                        .showImageOnLoading(R.drawable.healthy_icon01)
                        .cacheInMemory(true)
                        .cacheOnDisk(true)
                        .displayer(new SimpleBitmapDisplayer())
                        .bitmapConfig(Bitmap.Config.RGB_565)
                        .build();

                ImageLoader.getInstance().displayImage(url, holder.newsImage, options);
            }
        }
        return convertView;
    }

    static class ViewHolder{
        ImageView newsImage;
        TextView titleTextView;
    }

 @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        View view;
        if (convertView == null){
            view = LayoutInflater.from(context).inflate(R.layout.healthy_item,null);
        }else {
            view = convertView;
        }

        TextView healthy_title = (TextView) view.findViewById(R.id.healthy_title);
        healthy_title.setText(healthyList.get(position).getTitle());
        return view;
    }

我犯的错误是将TextView healthy_title = (TextView) view.findViewById(R.id.healthy_title);healthy_title.setText(healthyList.get(position).getTitle());这段代码写在了第一个if判断中，导致的结果就是如果covertView为空时，标题可以正常在页面上显示，一旦直接加入缓存时，标题就无法正常显示，就会出现很奇怪的错误，ListView中的标题各种错乱，其实应该在就可以想到是BaseAdapter中的错误的，还好我有足够的时间去纠正错误并从中学习到很多知识。

关于PullToRefreshListView的使用网上有很多的博客都有介绍。基本绑定adapter之后，可以通过setRefreshing（），直接显示刷新的页面。之后就是setOnRefreshListener()来监听滑动的判断，可以设置PullToRefresh的mode来设置上滑刷新、下滑刷新。

        @Override
            public void onPullUpToRefresh(PullToRefreshBase<ListView> refreshView) {  //上滑刷新
                //Toast.makeText(HealthyActivity.this,"上拉刷新",Toast.LENGTH_SHORT).show();
                String label = DateUtils.formatDateTime(getApplicationContext(),
                        System.currentTimeMillis(),
                        DateUtils.FORMAT_SHOW_TIME | DateUtils.FORMAT_SHOW_DATE | DateUtils.FORMAT_ABBREV_ALL);
                // Update the LastUpdatedLabel
                refreshView.getLoadingLayoutProxy().setLastUpdatedLabel(
                        "更新于" + " : " + label);

                asyncHttpClient.get(nextPageUrl,new AsyncHttpResponseHandler() {
                @Override
                public void onSuccess(int i, Header[] headers, byte[] bytes) {
                    try {
                        String str = new String(bytes,"gb2312");
                        Document document = Jsoup.parse(str);
                        Element body = document.body();
                        Elements tdWidth = body.select("td[width=500]");
                        Elements tdHeight = tdWidth.select("td[height=40]");
                        Elements links = tdHeight.select("a");
                        Log.d("hys",healthyList.toString());
                        for (Element link : links){
                            String title = link.text();
                            String url = link.attr("href");
                            healthy = new Healthy();
                            healthy.setTitle(title);
                            healthy.setUrl(url);
                            healthyList.add(healthy);
                        }

//
//
//                        Iterator<Healthy> iterator = healthyList.iterator();
//                        while (iterator.hasNext()){
//                            Healthy healthy = iterator.next();
//                            Log.d("hys","healthy1.getTitle() : "+healthy.getTitle());
//                        }

                        HealthyAdapter healthyAdapter = new HealthyAdapter(HealthyActivity.this,healthyList);

                        healthyAdapter.notifyDataSetChanged();
                        pullToRefreshListView.onRefreshComplete();

                        Elements link_more = body.select("a[href^=http://health.enorth.com.cn/system/more/]");
                        if (link_more.size() == 2){
                            nextPageUrl = link_more.get(1).attr("href");
                        }
                        else if (link_more.size() == 1){
                            nextPageUrl = link_more.get(0).attr("href");
                        }

                    }catch (IOException e){
                        Log.d("file read exception : ", e.getMessage());
                    }

                }

                @Override
                public void onFailure(int i, Header[] headers, byte[] bytes, Throwable throwable) {
                    Toast.makeText(HealthyActivity.this, "请检查网络连接", Toast.LENGTH_SHORT).show();
                    Log.d("asyncHttpClient fail : ",throwable.getMessage());
                }
            });
        }

    String label = DateUtils.formatDateTime(getApplicationContext(),System.currentTimeMillis(),

DateUtils.FORMAT_SHOW_TIME | DateUtils.FORMAT_SHOW_DATE | DateUtils.FORMAT_ABBREV_ALL);
                refreshView.getLoadingLayoutProxy().setLastUpdatedLabel(
                        "更新于" + " : " + label);

DateUtils是android.text.format包下的一个类，非常的好用，以后在时间方面可以多多使用这个方法。刷新结束必须healthyAdapter.notifyDataSetChanged();
                        pullToRefreshListView.onRefreshComplete();这两个方法，第一个用来提示数据加载完成，第二个表示刷新已经完成，刷新就会结束。另外在属性上可以对PullToRefreshListView进行属性上的定制，只要在xml文件中增加一个 xmlns:ptr="http://schemas.android.com/apk/res-auto" 的命名空间即可。

<?xml version="1.0" encoding="utf-8"?>
<resources>

    <declare-styleable name="PullToRefresh">

        <!-- A drawable to use as the background of the Refreshable View -->
        <!-- 设置刷新view的背景 -->
        <attr name="ptrRefreshableViewBackground" format="reference|color" />

        <!-- A drawable to use as the background of the Header and Footer Loading Views -->
        <!-- 设置头部view的背景 -->
        <attr name="ptrHeaderBackground" format="reference|color" />

        <!-- Text Color of the Header and Footer Loading Views -->
        <!-- 设置头部/底部文字的颜色 -->
        <attr name="ptrHeaderTextColor" format="reference|color" />

        <!-- Text Color of the Header and Footer Loading Views Sub Header -->
        <!-- 设置头部/底部副标题的文字颜色 -->
        <attr name="ptrHeaderSubTextColor" format="reference|color" />

        <!-- Mode of Pull-to-Refresh that should be used -->
        <!-- 设置下拉刷新的模式，有多重方式可选。无刷新功能，从顶部刷新，从底部刷新，二者都有，只允许手动刷新 -->
        <attr name="ptrMode">
            <flag name="disabled" value="0x0" />
            <flag name="pullFromStart" value="0x1" />
            <flag name="pullFromEnd" value="0x2" />
            <flag name="both" value="0x3" />
            <flag name="manualOnly" value="0x4" />

            <!-- These last two are depreacted -->
            <!-- 这两个属性不推荐了，用上面的代替即可 -->
            <flag name="pullDownFromTop" value="0x1" />
            <flag name="pullUpFromBottom" value="0x2" />
        </attr>

        <!-- Whether the Indicator overlay(s) should be used -->
        <!-- 是否显示指示箭头 -->
        <attr name="ptrShowIndicator" format="reference|boolean" />

        <!-- Drawable to use as Loading Indicator. Changes both Header and Footer. -->
        <!-- 指示箭头的图片 -->
        <attr name="ptrDrawable" format="reference" />

        <!-- Drawable to use as Loading Indicator in the Header View. Overrides value set in ptrDrawable. -->
        <!-- 顶部指示箭头的图片，设置后会覆盖ptrDrawable中顶部的设置 -->
        <attr name="ptrDrawableStart" format="reference" />

        <!-- Drawable to use as Loading Indicator in the Fooer View. Overrides value set in ptrDrawable. -->
        <!-- 底部指示箭头的图片，设置后会覆盖ptrDrawable中底部的设置 -->
        <attr name="ptrDrawableEnd" format="reference" />

        <!-- Whether Android's built-in Over Scroll should be utilised for Pull-to-Refresh. -->
        <attr name="ptrOverScroll" format="reference|boolean" />

        <!-- Base text color, typeface, size, and style for Header and Footer Loading Views -->
        <!-- 设置文字的基本字体 -->
        <attr name="ptrHeaderTextAppearance" format="reference" />

        <!-- Base text color, typeface, size, and style for Header and Footer Loading Views Sub Header -->
        <!-- 设置副标题的基本字体 -->
        <attr name="ptrSubHeaderTextAppearance" format="reference" />

        <!-- Style of Animation should be used displayed when pulling. -->
        <!-- 设置下拉时标识图的动画，默认为rotate -->
        <attr name="ptrAnimationStyle">
            <flag name="rotate" value="0x0" />
            <flag name="flip" value="0x1" />
        </attr>

        <!-- Whether the user can scroll while the View is Refreshing -->
        <!-- 设置刷新时是否允许滚动，一般为true -->
        <attr name="ptrScrollingWhileRefreshingEnabled" format="reference|boolean" />

        <!--
            Whether PullToRefreshListView has it's extras enabled. This allows the user to be 
            able to scroll while refreshing, and behaves better. It acheives this by adding
            Header and/or Footer Views to the ListView.
        -->
        <!-- 允许在listview中添加头/尾视图 -->
        <attr name="ptrListViewExtrasEnabled" format="reference|boolean" />

        <!--
            Whether the Drawable should be continually rotated as you pull. This only
            takes effect when using the 'Rotate' Animation Style.
        -->
        <!-- 当设置rotate时，可以用这个来设置刷新时旋转的图片 -->
        <attr name="ptrRotateDrawableWhilePulling" format="reference|boolean" />

        <!-- BELOW HERE ARE DEPRECEATED. DO NOT USE. -->
        <attr name="ptrAdapterViewBackground" format="reference|color" />
        <attr name="ptrDrawableTop" format="reference" />
        <attr name="ptrDrawableBottom" format="reference" />
    </declare-styleable>

</resources>

最后完成了从网页读取信息，展示在手机上的效果，并且完善了之前功能的下拉刷新部分。不过对于html的文本在android设备图片显示的问题依然没有得到非常完美的解决办法。实在无法处理网页中的图片在Andorid设备上的布局和大小，希望之后能获得一个完美的解决方案。