Android开发之控件ListView的使用技巧

• convertViwe的复用
  我们借助给view打tag的方式来复用放在内存中的view

@Override
public View getView(final int i, View view, ViewGroup viewGroup) {
    // 数据源
    item = getItem(i);
    ViewHolder viewHolder;
    if (view == null || view.getTag() == null) {
        view = LayoutInflater.from(getContext()).inflate(R.layout.course_online_cell, null);
        viewHolder = new ViewHolder();
        viewHolder.tv_online_course_title = view.findViewById(tv_online_course_title);
        viewHolder.tv_online_course_hot = view.findViewById(R.id.tv_online_course_hot);
        viewHolder.iv_course_online_thumbnail = view.findViewById(R.id.iv_course_online_thumbnail);

        ImageLoader.getInstance().displayImage(item.optString("thumbnail"), viewHolder.iv_course_online_thumbnail, displayImageOptions);
        viewHolder.iv_course_online_thumbnail.setTag(item.optInt("courseId") + "");
        view.setTag(viewHolder);
    } else {
        viewHolder = (ViewHolder) view.getTag();
        if (!viewHolder.iv_course_online_thumbnail.getTag().equals(item.optInt("courseId") + "")) {
            ImageLoader.getInstance().displayImage(item.optString("thumbnail"), viewHolder.iv_course_online_thumbnail, displayImageOptions);
            viewHolder.iv_course_online_thumbnail.setTag(item.optInt("courseId") + "");
        }
    }
    // 标题
    viewHolder.tv_online_course_title.setText(item.optString("title"));
    // 报名人数
    String enrollNumber = getContext().getResources().getString(R.string.enrollNumber);
    viewHolder.tv_online_course_hot.setText(String.format(enrollNumber, item.optString("enrollNum")));
    // 课程封面图
    viewHolder.iv_course_online_thumbnail.setScaleType(ImageView.ScaleType.CENTER_CROP);

    return view;
}

static class ViewHolder {
    TextView tv_online_course_title;
    TextViewNumber tv_online_course_hot;
    ImageView iv_course_online_thumbnail;
}

• 滑动操作图片闪烁
  如果是参考上面的代码重载的getView方法便不会出现滑动图片闪烁的问题，闪烁的原因就是我们的ImageView被重新加载了一遍（因为当ListView区域被滑动的时候，VisibleView发生了变化，会重新调用我们的getView方法，viewHolder会辅助我们对inflate出来的view打tag，那再重新调用getView的时候，如果这个view已经被打了tag就不必重新inflate，也不必findViewById去寻找布局UI控件，这是其中一个优化点，但是出现闪烁的原因了，每次getView我们都会重新渲染我们的图片，尽管调用的是缓存，但是只能保证这个闪烁是短暂的，当然如果没调用缓存图片，那就是较长时间的白屏了），那如何才能避免这一问题呢？那就是对ImageView也打一个tag，我们把核心代码抠出来，大家可以看一下。

 ViewHolder viewHolder;
 if (view == null || view.getTag() == null) {
     view = LayoutInflater.from(getContext()).inflate(R.layout.course_online_cell, null);
     viewHolder = new ViewHolder();
     viewHolder.iv_course_online_thumbnail = view.findViewById(R.id.iv_course_online_thumbnail);

     ImageLoader.getInstance().displayImage(item.optString("thumbnail"), viewHolder.iv_course_online_thumbnail, displayImageOptions);
     viewHolder.iv_course_online_thumbnail.setTag(item.optInt("courseId") + "");
     view.setTag(viewHolder);
 } else {
     viewHolder = (ViewHolder) view.getTag();
     if (!viewHolder.iv_course_online_thumbnail.getTag().equals(item.optInt("courseId") + "")) {
         ImageLoader.getInstance().displayImage(item.optString("thumbnail"), viewHolder.iv_course_online_thumbnail, displayImageOptions);
         viewHolder.iv_course_online_thumbnail.setTag(item.optInt("courseId") + "");
     }
 }

• 数据更新
  由于从服务端拿到的数据是json形式，所以我放在BaseAdapter内的数据是JSONArray格式，上面其实已经暴露了一部分代码了，我们在这里只讲BaseAdapter内的数据（JSONArray list）如何更新？
  因为我是从js转过来的，所以对js 中array丰富的api印象很深刻，在开发过程中是非常灵活的，但是当我看完JSONArray的api后感觉很不适应，基本满足不了开发需要，所以我写了一个JSONArray的工具类，基本涵盖了所有设计到的操作。
  • add(JSONArray array, JSONObject object)
  • add(JSONArray array1, JSONArray array2)
  • add(int index, JSONArray array, JSONObject object)
  • add(int index, JSONArray array1, JSONArray array2)
  • replice(int index, int length, JSONArray list)
  • replice(int index, int length, JSONArray list, JSONObject object)
  • replice(int index, int length, JSONArray array1, JSONArray array2)
  • reset(JSONArray list)

import android.util.Log;
import org.json.JSONArray;
import org.json.JSONObject;

public class JSONArrayHelper {

    /**
     * add(JSONArray array, JSONObject object)
     * add(JSONArray array1, JSONArray array2)
     * @param jsonArray
     * @param t
     * @param 
     * @return
     */
    public static <T> JSONArray add(JSONArray jsonArray, T t) {

        String type = t.getClass().getSimpleName();
        switch (type) {
            case "JSONObject":
                jsonArray.put(t);
                return jsonArray;
            case "JSONArray":
                return joinJSONArray((JSONArray) t, jsonArray);
                default:
                    return jsonArray;
        }
    }

    /**
     * add(int index, JSONArray array, JSONObject object)
     * add(int index, JSONArray array1, JSONArray array2)
     * @param index
     * @param jsonArray
     * @param t
     * @param 
     * @return
     */
    public static <T> JSONArray add(int index, JSONArray jsonArray, T t) {

        String type = t.getClass().getSimpleName();
        switch (type) {
            case "JSONObject":
                return joinJSONArray(index, jsonArray, (JSONObject) t);
            case "JSONArray":
                return joinJSONArray(index, jsonArray, (JSONArray) t);
            default:
                return jsonArray;
        }
    }

    /**
     * replice(int index, int length, JSONArray list)
     * @param index
     * @param length
     * @param jsonArray
     * @param 
     * @return
     */
    public static <T> JSONArray replice(int index, int length, JSONArray jsonArray) {
        return repliceJSONArray(index, length, jsonArray);
    }

    /**
     * replice(int index, int length, JSONArray list, JSONObject object)
     * replice(int index, int length, JSONArray array1, JSONArray array2)
     * @param index
     * @param length
     * @param jsonArray
     * @param t
     * @param 
     * @return
     */
    public static <T> JSONArray replice(int index, int length, JSONArray jsonArray, T t) {

        if (length == 0) return add(index, jsonArray, t);

        String type = t.getClass().getSimpleName();
        switch (type) {
            case "JSONObject":
                return repliceJSONArray(index, length, jsonArray, (JSONObject) t);
            case "JSONArray":
                return repliceJSONArray(index, length, jsonArray, (JSONArray) t);
            default:
                return jsonArray;
        }
    }

    /**
     * reset(JSONArray list)
     * @param jsonArray
     * @return
     */
    public static JSONArray reset (JSONArray jsonArray) {
        return jsonArray;
    }


    public static JSONArray joinJSONArray (JSONArray array1, JSONArray array2) {
        if (array1.length() == 0) return array2;
        if (array2.length() == 0) return array1;

        StringBuffer buffer = new StringBuffer();
        try {

            int len = array1.length();
            for (int i = 0; i < len; i++) {
                JSONObject obj1 = (JSONObject) array1.get(i);
                if (i == len - 1)
                    buffer.append(obj1.toString());
                else
                    buffer.append(obj1.toString()).append(",");
            }

            len = array2.length();
            if (len > 0)
                buffer.append(",");
            for (int i = 0; i < len; i++) {
                JSONObject obj1 = (JSONObject) array2.get(i);
                if (i == len - 1)
                    buffer.append(obj1.toString());
                else
                    buffer.append(obj1.toString()).append(",");
            }
            buffer.insert(0, "[").append("]");

            return new JSONArray(buffer.toString());
        } catch (Exception e) {
            return new JSONArray();
        }
    }

    public static JSONArray joinJSONArray (int index, JSONArray array1, JSONArray array2) {

        if (array1.length() == 0) return array2;
        if (array2.length() == 0) return array1;

        StringBuffer buffer = new StringBuffer();
        try {
            int len1 = array1.length();
            int len2 = array2.length();

            if (index < len1) {
                for (int i = 0; i < len1; i++) {
                    JSONObject obj1 = (JSONObject) array1.get(i);

                    if (i == index) {
                        for (int j = 0; j < len2; j++) {
                            JSONObject obj2 = (JSONObject) array2.get(j);
                            buffer.append(obj2.toString()).append(",");
                        }

                        if (i == len1 - 1)
                            buffer.append(obj1.toString());
                        else
                            buffer.append(obj1.toString()).append(",");

                    } else {
                        if (i == len1 - 1)
                            buffer.append(obj1.toString());
                        else
                            buffer.append(obj1.toString()).append(",");
                    }
                }

            } else {

                for (int i = 0; i < len1; i++) {
                    JSONObject obj1 = (JSONObject) array1.get(i);
                    if (i == len1 - 1)
                        buffer.append(obj1.toString());
                    else
                        buffer.append(obj1.toString()).append(",");
                }

                if (len2 > 0)
                    buffer.append(",");

                for (int j = 0; j < len2; j++) {
                    JSONObject obj2 = (JSONObject) array2.get(j);
                    if (j == len2 - 1)
                        buffer.append(obj2.toString());
                    else
                        buffer.append(obj2.toString()).append(",");
                }
            }

            buffer.insert(0, "[").append("]");
            return new JSONArray(buffer.toString());
        } catch (Exception e) {
            return new JSONArray();
        }
    }

    public static JSONArray joinJSONArray (int index, JSONArray jsonArray, JSONObject jsonObject) {

        int len = jsonArray.length();
        if (len == 0 || index > len - 1) return jsonArray.put(jsonObject);

        StringBuffer buffer = new StringBuffer();
        try {

            for (int i = 0; i < len; i++) {
                JSONObject obj = (JSONObject) jsonArray.get(i);

                if (i == index) {
                    buffer.append(jsonObject.toString()).append(",");

                    if (i == len - 1)
                        buffer.append(obj.toString());
                    else
                        buffer.append(obj.toString()).append(",");
                } else {
                    if (i == len - 1)
                        buffer.append(obj.toString());
                    else
                        buffer.append(obj.toString()).append(",");
                }
            }

            buffer.insert(0, "[").append("]");
            return new JSONArray(buffer.toString());

        } catch (Exception e) {
            return new JSONArray();
        }
    }

    public static JSONArray repliceJSONArray(int index, int length, JSONArray jsonArray) {

        int len = jsonArray.length();
        if (len == 0 || index >= length) return jsonArray;

        StringBuffer buffer = new StringBuffer();
        try {

            for (int i = 0; i < len; i++) {
                JSONObject obj1 = (JSONObject) jsonArray.get(i);

                if (i < index || i > index + length -1) {
                    if (i == len - 1)
                        buffer.append(obj1.toString());
                    else
                        buffer.append(obj1.toString()).append(",");
                }
            }

            buffer.insert(0, "[").append("]");
            Log.e("JSONArrayHelper", buffer.toString());
            return new JSONArray(buffer.toString());

        } catch (Exception e) {
            return new JSONArray();
        }
    }

    public static JSONArray repliceJSONArray(int index, int length, JSONArray jsonArray, JSONObject jsonObject) {

        int len = jsonArray.length();
        if (len == 0 || index > len - 1) return jsonArray.put(jsonObject);

        StringBuffer buffer = new StringBuffer();
        try {

            for (int i = 0; i < len; i++) {
                JSONObject obj = (JSONObject) jsonArray.get(i);

                if (i >= index && i <= index + length - 1) {
                    if (i == index) {
                        buffer.append(jsonObject.toString());
                        if (i < len -1 && index + length - 1 < len - 1) buffer.append(",");
                    }
                } else {
                    if (i == len - 1)
                        buffer.append(obj.toString());
                    else
                        buffer.append(obj.toString()).append(",");
                }
            }

            buffer.insert(0, "[").append("]");
            return new JSONArray(buffer.toString());

        } catch (Exception e) {
            return new JSONArray();
        }
    }

    public static JSONArray repliceJSONArray(int index, int length, JSONArray array1, JSONArray array2) {

        int len1 = array1.length();
        int len2 = array2.length();
        if (len2 == 0) return array1;
        if (len1 == 0 || index > len1 - 1) return add(array1, array2);

        StringBuffer buffer = new StringBuffer();
        try {

            for (int i = 0; i < len1; i++) {
                JSONObject obj1 = (JSONObject) array1.get(i);

                if (i >= index && i <= index + length - 1) {
                    if (i == index)
                        for (int j = 0; j < len2; j++) {
                            JSONObject obj2 = (JSONObject) array2.get(j);

                            if (j == len2 - 1 && index + length - 1 >= len1 - 1)
                                buffer.append(obj2.toString());
                            else
                                buffer.append(obj2.toString()).append(",");
                        }
                } else {
                    if (i == len1 - 1)
                        buffer.append(obj1.toString());
                    else
                        buffer.append(obj1.toString()).append(",");
                }
            }

            buffer.insert(0, "[").append("]");
            Log.e("JSONArrayHelper", buffer.toString());
            return new JSONArray(buffer.toString());

        } catch (Exception e) {
            return new JSONArray();
        }
    }

}

• 下拉刷新
  为保证用户体验，正在加动画处理，待续
• 上拉加载
  为保证用户体验，正在加动画处理，待续