android BaseAdapter多布局緩衝

android BaseAdapter多布局緩衝

　ListView是App開發中最常見的控制項之一了，與之相隨的則是BaseAdapter的使用，BaseAdapter的作用則是為我們的ListView提供資料來源，普通的用法相信大家都會用，今天主要說明一下，列表中如果有多種樣式的ItemView時，應該如何去高效的載入．

　先看一下：

　

　：整個列表中存在著兩種樣式的ItemView,開始用傳統的ConvertView去緩衝子項時，發現兩種布局一滑動就出現了錯亂，後來為了項目進度，看到沒有發生記憶體溢出後就沒有用ConvertView做子View的緩衝，今天在翻看Adapter及其子類的源碼時發現，如下代碼，瞬間想到之前沒有對多布局多緩衝的問題，於是上網查看了一下，果然就是用這幾個方法去實現，代碼如下：

 

public interface Adapter {     void registerDataSetObserver(DataSetObserver observer);    void unregisterDataSetObserver(DataSetObserver observer);    int getCount();         Object getItem(int position);        long getItemId(int position);        boolean hasStableIds();        View getView(int position, View convertView, ViewGroup parent);　　 static final int IGNORE_ITEM_VIEW_TYPE = AdapterView.ITEM_VIEW_TYPE_IGNORE;        int getItemViewType(int position);　　//方法一，得到布局類型　        int getViewTypeCount();　　　　　　　// 方法二，得到布局總        static final int NO_SELECTION = Integer.MIN_VALUE;      /**      * @return true if this adapter doesn't contain any data.  This is used to determine      * whether the empty view should be displayed.  A typical implementation will return      * getCount() == 0 but since getCount() includes the headers and footers, specialized      * adapters might want a different behavior.      */     boolean isEmpty();}

　　就是紅色注釋出的兩個方法，而BaseAdapter已經幫我們提供了預設的實現，才使得我們沒有關注到這兩個方法，BaseAdapter的預設實現如下：

 

 

package android.widget;import android.database.DataSetObservable;import android.database.DataSetObserver;import android.view.View;import android.view.ViewGroup;public abstract class BaseAdapter implements ListAdapter, SpinnerAdapter {    private final DataSetObservable mDataSetObservable = new DataSetObservable();    public boolean hasStableIds() {        return false;    }        public void registerDataSetObserver(DataSetObserver observer) {        mDataSetObservable.registerObserver(observer);    }    public void unregisterDataSetObserver(DataSetObserver observer) {        mDataSetObservable.unregisterObserver(observer);    }       public void notifyDataSetChanged() {        mDataSetObservable.notifyChanged();    }        public void notifyDataSetInvalidated() {        mDataSetObservable.notifyInvalidated();    }    public boolean areAllItemsEnabled() {        return true;    }    public boolean isEnabled(int position) {        return true;    }    public View getDropDownView(int position, View convertView, ViewGroup parent) {        return getView(position, convertView, parent);    }    public int getItemViewType(int position) {        return 0;    }    public int getViewTypeCount() {        return 1;    }        public boolean isEmpty() {        return getCount() == 0;    }}

　有了這兩個方法後，我們只需重寫這兩個方法即可，下面是我重寫的Adapter代碼：

 

　

/********************************************************** * @檔案名稱：CountryListAdapter.java * @檔案作者：rzq * @建立時間：2014年7月22日 下午2:33:43 * @檔案描述：國家列表適配器 * @修改曆史：2014年7月22日建立初始版本 **********************************************************/public class CountryListAdapter extends BaseAdapter {private Context mContext;private ArrayList dataList;private Country country;private ViewHolder holder1;private ViewHolder holder2;public CountryListAdapter(Context context, ArrayList dataList) {this.mContext = context;this.dataList = dataList;}@Overridepublic int getCount() {return dataList.size();}@Overridepublic Object getItem(int position) {return dataList.get(position);}@Overridepublic long getItemId(int position) {return 0;}@Overridepublic View getView(int position, View convertView, ViewGroup parent) {country = (Country) dataList.get(position);int type = getItemViewType(position);if (convertView == null) {switch (type) {case 0:holder1 = new ViewHolder();convertView = LayoutInflater.from(mContext).inflate(R.layout.catagories_expandlistview_group,parent, false);holder1.textView = (TextView) convertView.findViewById(R.id.catagories_group_textview);convertView.setTag(holder1);break;case 1:holder2 = new ViewHolder();convertView = LayoutInflater.from(mContext).inflate(R.layout.register_expandlistview_child, parent, false);holder2.textView = (TextView) convertView.findViewById(R.id.register_child_textview);holder2.imageView = (ImageView) convertView.findViewById(R.id.register_country_flag);convertView.setTag(holder2);break;}} else {switch (type) {case 0:holder1 = (ViewHolder) convertView.getTag();break;case 1:holder2 = (ViewHolder) convertView.getTag();break;}}switch (type) {case 0:holder1.textView.setText(country.getIndexChar());break;case 1:holder2.textView.setText(country.getCountryName());holder2.imageView.setImageDrawable(country.getFlagDrawable());break;}return convertView;}@Overridepublic int getItemViewType(int position) {country = (Country) getItem(position);if (country.isGroup()) {return 0;} else {return 1;}}@Overridepublic int getViewTypeCount() {return 2;}private static class ViewHolder {private TextView textView;private ImageView imageView;}}

這樣確保了記憶體不會溢出．也可以提高ListView的載入效率．