关于Flex的DataGrid的应用拓展（三）

     DataGrid自身的排序组件可谓做的非常全面，而且非常好用。用户也可以自己实现排序算法。但有时我们需要实现一些额外的功能，如要实现数据库排序。就是当我点击某一列时，我希望实现数据库根据我的条件排序。实现排序这个功能并不难，只需要实现DataGridEvent.HEADER_RELEASE的Listener即可，但要实现排序箭头的存在可能就需要费一番周折。        这里我提供三种方法         1）复写header 类，把箭头（sortArrow）去掉。同时自己整两个图片放在那里，手工控制一下。这个思路没有实现过，据说可能；         2）复写DataGrid的dataProvider方法。对传入的值进行排序，这样就会出现箭头。如下面的实现步骤：               
（1）实现对 dataProvider 的复写   
      

  /**
         * override current dataProvider to call refresh column
         */ 
        [Inspectable(category="Data", defaultValue="undefined")]
        override public function set dataProvider(value:Object):void
        {
         super.dataProvider=value;
         checkorderArrow();
        }                  （2）实现上面调用的方法： /**
         * order current column,purpose to show Arrow,
         * note: not used function
         */ 
        public function checkorderArrow():void{
            if(dataProvider&&currentsortColumn){
                var coll:ArrayCollection=dataProvider as ArrayCollection;
                coll.sort = new Sort();
                var field:SortField=new SortField(currentsortColumn.dataField, true, currentsortColumn.sortDescending);
                if(currentsortColumn.isNumberic){
                    field.compareFunction=sortFunction;
                }
                coll.sort.fields = [field];
               coll.refresh();
               mx_internal::sortDirection=currentsortColumn.sortDescending;
               
            }
        }  

  
注：这个方法中用到了currentsortColumn，这个是要在headerRelease时需要记住的列。
        3)第三种方法和第二种方法不同的地方是在排序的实现上，如以下的代码：
     

  /**
         *  @private  
         *   sort current column  ,its code is from datagrid
         */
        private function sortByColumn():void
        {
            if(!currentsortColumn){
                return;
            }
            var c:SessionDataGridColumn = currentsortColumn;
            var desc:Boolean = c.sortDescending;
            
            // do the sort if we're allowed to
            if (c.sortable)
            {
                var s:Sort = collection.sort;
                var f:SortField;
                if (s)
                {
                    s.compareFunction = null;
                    // analyze the current sort to see what we've been given
                    var sf:Array = s.fields;
                    if (sf)
                    {
                        for (var i:int = 0; i < sf.length; i++)
                        {
                            
                            if (sf[i].name == c.dataField)
                            {
                                // we're part of the current sort
                                f = sf[i]
                                // flip the logic so desc is new desired order
                                desc = !f.descending;
                                break;
                            }
                        }
                    }
                }
                else
                    s = new Sort;
                
                if (!f)
                    f = new SortField(c.dataField);
                
                
                c.sortDescending = desc;
                var dir:String = (desc) ? "DESC" : "ASC";
                sortDirection = dir;
                
                // set the grid's sortIndex
                lastSortIndex = sortIndex;
                sortIndex = point[1];
                
                // if you have a labelFunction you must supply a sortCompareFunction
                f.name = c.dataField;
                if (c.sortCompareFunction != null)
                {
                    f.compareFunction = c.sortCompareFunction;
                }
                else
                {
                    f.compareFunction = null;
                }
                f.descending = desc;
                s.fields = [f];
            }
            collection.sort = s;
            collection.refresh();
            
        }

上面这两种方法说的都不是特别细。以下是整个类的代码（第二种和第三种的实现）供参考：

package {
    import mx.collections.ArrayCollection;
    import mx.collections.Sort;
    import mx.collections.SortField;
    import mx.controls.DataGrid;
    import mx.controls.dataGridClasses.DataGridColumn;
    import mx.core.mx_internal;
    import mx.events.DataGridEvent;
    import mx.utils.ObjectUtil;
    
    /**
    * added a cutomer datagrid for database sorting
    */ 
    public class SortDatabaseDatagrid extends DataGrid
    {
        
        use namespace mx_internal; 

        public function SortDatabaseDatagrid()
        {
            super();
            this.addEventListener(DataGridEvent.HEADER_RELEASE,function(evt:DataGridEvent):void{
                evt.currentTarget.currentsortColumn=DataGridColumn(evt.currentTarget.columns[evt.columnIndex]);
                point[0]=evt.rowIndex;
                point[1]=evt.columnIndex;
            });
        }
        
        private var point:Array=[];
        //remember current clicking column
        private var _currentsortColumn:SessionDataGridColumn;
        
        public function get currentsortColumn():SessionDataGridColumn
        {
            return _currentsortColumn;
        }
        
        public function set currentsortColumn(value:SessionDataGridColumn):void
        {
            _currentsortColumn = value;
        }
        
        
      
        /**
         * order current column,purpose to show Arrow,
         * note: not used function
         */ 
        public function checkorderArrow():void{
            if(dataProvider&¤tsortColumn){
                var coll:ArrayCollection=dataProvider as ArrayCollection;
                coll.sort = new Sort();
                var field:SortField=new SortField(currentsortColumn.dataField, true, currentsortColumn.sortDescending);
                if(currentsortColumn.isNumberic){
                    field.compareFunction=sortFunction;
                }
                coll.sort.fields = [field];
               coll.refresh();
               mx_internal::sortDirection=currentsortColumn.sortDescending;
               
            }
        }
        
        
        /**
         *  @private  
         *   sort current column  ,its code is from datagrid
         */
        private function sortByColumn():void
        {
            if(!currentsortColumn){
                return;
            }
            var c:SessionDataGridColumn = currentsortColumn;
            var desc:Boolean = c.sortDescending;
            
            // do the sort if we're allowed to
            if (c.sortable)
            {
                var s:Sort = collection.sort;
                var f:SortField;
                if (s)
                {
                    s.compareFunction = null;
                    // analyze the current sort to see what we've been given
                    var sf:Array = s.fields;
                    if (sf)
                    {
                        for (var i:int = 0; i < sf.length; i++)
                        {
                            
                            if (sf[i].name == c.dataField)
                            {
                                // we're part of the current sort
                                f = sf[i]
                                // flip the logic so desc is new desired order
                                desc = !f.descending;
                                break;
                            }
                        }
                    }
                }
                else
                    s = new Sort;
                
                if (!f)
                    f = new SortField(c.dataField);
                
                
                c.sortDescending = desc;
                var dir:String = (desc) ? "DESC" : "ASC";
                sortDirection = dir;
                
                // set the grid's sortIndex
                lastSortIndex = sortIndex;
                sortIndex = point[1];
                
                // if you have a labelFunction you must supply a sortCompareFunction
                f.name = c.dataField;
                if (c.sortCompareFunction != null)
                {
                    f.compareFunction = c.sortCompareFunction;
                }
                else
                {
                    f.compareFunction = null;
                }
                f.descending = desc;
                s.fields = [f];
            }
            collection.sort = s;
            collection.refresh();
            
        }
     }
}