android中的ListView总结

最新推荐文章于 2022-05-11 03:44:12 发布

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本文介绍ListView控件在Android开发中的多种高级应用技巧，包括如何创建带Separators的List、实现带首字母索引的列表效果、从底部增加ITEM的对话式ListView、实现不滚动时异步加载的ListView以及提高Adapter效率的方法。

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ListView作为列表的常用控件,

通常使用MVC的模式来应用,

View自身就是V, 而C是所需要的adapter

一般情况下可以使用ArrayAdapter,CursorAdapter,BaseAdapter的实现类来绑定数据源

常见技巧(来源于API DEMOS,其他设置单选多选,cursor的使用,添加图片等参见Views/Lists中例子)

1.带Separators的List,从而该行可以显示但没有click效果与事件

adapter重写某些属性函数

   @Override
        public boolean areAllItemsEnabled() {
            return false;
        }

        @Override
        public boolean isEnabled(int position) {
            return !mStrings[position].startsWith("-");
        }

2.带首字母索引的列表效果(带屏幕中间的字母图)

设置onScroll监听,判断firstVisibleItem中的首字母

 public void onScroll(AbsListView view, int firstVisibleItem,
            int visibleItemCount, int totalItemCount) {
        if (mReady) {
            char firstLetter = mStrings[firstVisibleItem].charAt(0);
            
            if (!mShowing && firstLetter != mPrevLetter) {

                mShowing = true;
                mDialogText.setVisibility(View.VISIBLE);
            }
            mDialogText.setText(((Character)firstLetter).toString());
            mHandler.removeCallbacks(mRemoveWindow);
            mHandler.postDelayed(mRemoveWindow, 3000);
            mPrevLetter = firstLetter;
        }
    }

3.类似对话软件的ListView,从底部增加ITEM

 <ListView android:id="@android:id/list"
        android:layout_width="match_parent" 
        android:layout_height="0dip"
        android:layout_weight="1"
        android:stackFromBottom="true"
        android:transcriptMode="normal"/>

4.不滚动时异步加载的ListView

判断scrollState,当是IDLE时才去加载相应的ITEM

public void onScrollStateChanged(AbsListView view, int scrollState) {
        switch (scrollState) {
        case OnScrollListener.SCROLL_STATE_IDLE:
            mBusy = false;
            
            int first = view.getFirstVisiblePosition();// 当前第一个可见ITEM在LIST中位置
            int count = view.getChildCount();// 当前可见ITEM数目
            for (int i=0; i<count; i++) {
                TextView t = (TextView)view.getChildAt(i);
                if (t.getTag() != null) {
                    t.setText(mStrings[first + i]);
                    t.setTag(null);
                }
            }
            
            mStatus.setText("Idle");
            break;
        case OnScrollListener.SCROLL_STATE_TOUCH_SCROLL:// 手带着列表滑动,未离开屏幕
            mBusy = true;
            mStatus.setText("Touch scroll");
            break;
        case OnScrollListener.SCROLL_STATE_FLING:// 列表仍在滑动,手离开了屏幕,fling有冲的意思
            mBusy = true;
            mStatus.setText("Fling");
            break;
        }
    }

5.效率较高的adapter,较常用

 public View getView(int position, View convertView, ViewGroup parent) {
            // A ViewHolder keeps references to children views to avoid unneccessary calls
            // to findViewById() on each row.
            ViewHolder holder;

            // When convertView is not null, we can reuse it directly, there is no need
            // to reinflate it. We only inflate a new View when the convertView supplied
            // by ListView is null.
            if (convertView == null) {
                convertView = mInflater.inflate(R.layout.list_item_icon_text, null);

                // Creates a ViewHolder and store references to the two children views
                // we want to bind data to.
                holder = new ViewHolder();
                holder.text = (TextView) convertView.findViewById(R.id.text);
                holder.icon = (ImageView) convertView.findViewById(R.id.icon);

                convertView.setTag(holder);// 将引用保存到tag中
            } else {
                // Get the ViewHolder back to get fast access to the TextView
                // and the ImageView.
                holder = (ViewHolder) convertView.getTag();// 快速取回引用,减少了子view查找及引用赋值的时间
            }

            // Bind the data efficiently with the holder.
            holder.text.setText(DATA[position]);
            holder.icon.setImageBitmap((position & 1) == 1 ? mIcon1 : mIcon2);

            return convertView;
        }
	// 内部类,标明每个ITEM中的子内容
        static class ViewHolder {
            TextView text;
            ImageView icon;
        }