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Android：ListView、BaseAdapter、convertView、ListView优化及事件、notifyDataSetCh...

2017-11-22 657
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@Override
protected  void  onCreate(Bundle savedInstanceState)
{
     super .onCreate(savedInstanceState);
     setContentView(R.layout.activity_main);
                                                                                                                               
     final  ArrayList<String> title =  new  ArrayList<String>();
     for  ( int  i =  0 ; i <  20 ; i++)
     {
         title.add( "标题"  + i);
     }
                                                                                                                               
     ListView listView = (ListView) findViewById(R.id.listView1);
     listView.setAdapter( new  BaseAdapter()
     {
         @Override
         public  View getView( int  position, View convertView, ViewGroup parent) //执行数等于当前页面出现的行数,convertView指滚动消失的layout
         {
             Log.e( "getView" ,  "调用getView" + i++ +  "convertView:"  + convertView);
             LayoutInflater inf = getLayoutInflater(); //通过LayoutInflater将布局id转换到对象
             RelativeLayout relativeLayout = (RelativeLayout) inf.inflate(R.layout.relat,  null );
             TextView titleview = (TextView) relativeLayout.findViewById(R.id.textView1); //通过布局找到里面的控件
             titleview.setText(title.get(position)); //得到容器内的内容
             return  relativeLayout;
         }
                                                                                                                                   
         @Override
         public  long  getItemId( int  position)
         {
             return  0 ;
         }
                                                                                                                                   
         @Override
         public  Object getItem( int  position)
         {
             return  null ;
         }
                                                                                                                                   
         @Override
         //先执行getCount再执行getView，出现新行数时再次执行getCount
         //listview清单里要设置高度match_parent
         //每次点击屏幕一次都会先执行getCount
         public  int  getCount()
         {
             Log.e( "getCount" ,  "调用getCount" + j++);
             return  title.size();
         }
     });
}




复用converview：

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ListView listView = (ListView) findViewById(R.id.listView1);
listView.setAdapter( new  BaseAdapter()
{
     @Override
     public  View getView( int  position, View convertView, ViewGroup parent) //执行数等于当前页面出现的行数,convertView指滚动消失的layout
     {        
         //复用converview
         RelativeLayout relativeLayout =  null ;
         if (convertView ==  null )
         {
             LayoutInflater inf = getLayoutInflater();
             relativeLayout = (RelativeLayout) inf.inflate(R.layout.relat,  null );
         }
         else
         {
             relativeLayout = (RelativeLayout) convertView;
         }
                                                                                                                   
         TextView titleView = (TextView) relativeLayout.findViewById(R.id.textView1);
         titleView.setText(title.get(position));
         return  relativeLayout;
     }




继续优化：

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public  class  MainActivity  extends  Activity
{
     int  imID =  0 ;
     class  Msg //内容
     {
         String mTitle;
         String mSubtitle;
         String mTime;
         int  mImagID;
         public  Msg(String mTitle, String mSubtitle, String mTime,  int  mImagID)
         {
             super ();
             this .mTitle = mTitle;
             this .mSubtitle = mSubtitle;
             this .mTime = mTime;
             this .mImagID = mImagID;
         }
                                                                                                            
     }
                                                                                                        
     class  ViewHolder //控件
     {
         TextView viewTitle;
         TextView viewSubtitle;
         TextView viewTime;
         ImageView viewImage;
     }
     @Override
     protected  void  onCreate(Bundle savedInstanceState)
     {
         super .onCreate(savedInstanceState);
         setContentView(R.layout.activity_main);
                                                                                                            
         Date timeNow =  new  Date();
         SimpleDateFormat timeFormat =  new  SimpleDateFormat( "HH:mm:ss" );
         String time = timeFormat.format(timeNow);
                                                                                                            
         final  ArrayList<Msg> msgList =  new  ArrayList<Msg>();
         for  ( int  i =  0 ; i <  30 ; i++) //选择图片
         {
                                                                                                                
             if (i %  4  ==  0 )
             {
                 imID = R.drawable.ic_launcher;
             }
             if (i %  4  ==  1 )
             {
                 imID = R.drawable.ic_1;
             }
             if (i %  4  ==  2 )
             {
                 imID = R.drawable.ic_2;
             }
             if (i %  4  ==  3 )
             {
                 imID = R.drawable.ic_3;
             }
                                                                                                                
             Msg msg =  new  Msg( "标题"  + i,  "内容"  + i, time ,imID);
             msgList.add(msg);
         }
                                                                                                            
         ListView listView = (ListView) findViewById(R.id.listView1);
         listView.setAdapter( new  BaseAdapter()
         {
             ViewHolder holder =  null ;
             @Override
             public  View getView( int  position, View convertView, ViewGroup parent)
             {
                 RelativeLayout relout =  null ;
                 if  (convertView ==  null ) //创建首页时才find控件
                 {
                     LayoutInflater layoutInflater =getLayoutInflater();
                     relout = (RelativeLayout) layoutInflater.inflate(R.layout.relaout,  null );
                                                                                                                        
                     holder =  new  ViewHolder();
                     holder.viewTitle= (TextView) relout.findViewById(R.id.textView_title);
                     holder.viewSubtitle = (TextView) relout.findViewById(R.id.textView_subtitle);
                     holder.viewTime = (TextView) relout.findViewById(R.id.textView_time);
                     holder.viewImage = (ImageView) relout.findViewById(R.id.imageView1);
                                                                                                                        
                     relout.setTag(holder);
                 }
                 else //否则复用layout和view
                 {
                     relout = (RelativeLayout) convertView;
                     holder = (ViewHolder) relout.getTag(); //记得得到holder
                                                                                                                        
                 }
                                                                                                                    
                 Msg msg = msgList.get(position);
                                                                                                                    
                 holder.viewTitle.setText(msg.mTitle);
                 holder.viewSubtitle.setText(msg.mSubtitle);
                 holder.viewTime.setText(msg.mTime);
                 holder.viewImage.setImageResource(msg.mImagID); //设置图片的方法
                 return  relout;
             }
                                                                                                                
             @Override
             public  long  getItemId( int  position)
             {
                 return  0 ;
             }
                                                                                                                
             @Override
             public  Object getItem( int  position)
             {
                 return  null ;
             }
                                                                                                                
             @Override
             public  int  getCount()
             {
                 return  msgList.size();
             }
         });
     }
                                                                                                        
     @Override
     public  boolean  onCreateOptionsMenu(Menu menu)
     {
         getMenuInflater().inflate(R.menu.activity_main, menu);
         return  true ;
     }
                                                                                                        
}



点击按钮更新listview：Adapter使用notifyDataSetChanged()通知listview更新

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private  void  btn1Click() //增加一行信息
{
     i++;
     data.add( "内容"  + i );
     arrAdapter.notifyDataSetChanged(); //Adapter通知listview做更新
}
private  void  btn2Click() //删除第一行信息
{
     if (data.size() <  1 )
     {
        Toast.makeText( this ,  "信息已删除完毕！" , Toast.LENGTH_LONG).show();
     }
     else
     {
         data.remove( 0 );
         arrAdapter.notifyDataSetChanged(); //Adapter通知listview做更新
     }
}
private  void  btnsortClick() //对列表进行排序
{
     Collections.sort(data);
     arrAdapter.notifyDataSetChanged();
}



注：

1.LayoutInflater inflater = getLayoutInflater();

 layout = (RelativeLayout) inflater.inflate(R.layout.relayout, null);

 layout要通过LayoutInflater拿到。

2.getView返回layout，getCount()返回int。

3.layout.getTag()要转换为holder = (ViewHolder)。





本文转自 glblong 51CTO博客，原文链接：http://blog.51cto.com/glblong/1201270，如需转载请自行联系原作者
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