echarts自定义图例的点击事件

修改图例点击事件样例代码：

• 当第一次点击图例时，只显示点击的图例。
• 当还剩一个图例被取消选中后，自动全选中所有图例。

  var triggerAction = function(action, selected) {
        legend = [];

        for ( name in selected) {
            if (selected.hasOwnProperty(name)) {
                legend.push({name: name});
            }
        }

        myChart.dispatchAction({
            type: action,
            batch: legend
        });
    };

    var isFirstUnSelect = function(selected) {

        var unSelectedCount = 0;
        for ( name in selected) {
            if (!selected.hasOwnProperty(name)) {
                continue;
            }

            if (selected[name] == false) {
                ++unSelectedCount;
            }
        }
        return unSelectedCount==1;
    };

    var isAllUnSelected = function(selected) {
        var selectedCount = 0;
        for ( name in selected) {
            if (!selected.hasOwnProperty(name)) {
                continue;
            }

            // 所有 selected Object 里面 true 代表 selected， false 代表 unselected
            if (selected[name] == true) {
                ++selectedCount;
            }
        }
        return selectedCount==0;
    };

    myChart.on('legendselectchanged', function(obj) {
        var selected = obj.selected;
        var legend = obj.name;

        // 使用 legendToggleSelect Action 会重新触发 legendselectchanged Event，导致本函数重复运行
        // 使得 无 selected 对象
        if (selected != undefined) {

            if (isFirstUnSelect(selected)) {
                triggerAction('legendToggleSelect', selected);
            } else if (isAllUnSelected(selected)) {
                triggerAction('legendSelect', selected);

            }
        }

    });