Google visualization 谷歌可视化API-堆叠条形图-自定义工具提示

我一直在尝试获取堆叠条形图的自定义工具提示

var data = new google.visualization.DataTable();
data.addColumn('string', 'Units');
data.addColumn('number', '1');
data.addColumn('number', '2');
data.addColumn('number', '3');
data.addColumn('number', '4');

_1 = 0.123
_2 = 0.23
_3 = 0.3
_4 = 0

data.addRow([_units, _1, _2, _3, _4,]);

var options = {
        isStacked: true,
        height: 150,
        chartArea: { height: 50 },
        legend: { position: 'top' },
};

bchart = new google.visualization.BarChart(bcontainer);
bchart.draw(data, options);

那么，我的问题是如何为以下每一项创建工具提示：_1、_2、_3、_4

---

谢谢

下面的谷歌文档中介绍了这一点

在条形图文档中，它解释了哪些角色可用于该图表

您需要做的是向数据中添加{role:tooltip}附加列，该列显示您希望工具提示显示的内容

例如：

  var data = new google.visualization.DataTable();
  data.addColumn('string', 'Year');
  data.addColumn('number', 'Sales');
  data.addColumn({type: 'string', role: 'tooltip'});
  data.addColumn('number', 'Expenses');
  data.addColumn({type: 'string', role: 'tooltip'});
  data.addRows([
    ['2004', 1000, '1M$ sales in 2004', 400,  '$0.4M expenses in 2004'],
    ['2005', 1170, '1.17M$ sales in 2005', 460, '$0.46M expenses in 2005'],
    ['2006', 660,  '.66$ sales in 2006', 1120, '$1.12M expenses in 2006'],
    ['2007', 1030, '1.03M$ sales in 2007', 540, '$0.54M expenses in 2007']
  ]);

最终代码如下所示：

function drawVisualization() {
  // Create and populate the data table.
  var data = new google.visualization.DataTable();
  data.addColumn('string', 'Year');
  data.addColumn('number', 'Sales');
  data.addColumn({type: 'string', role: 'tooltip'});
  data.addColumn('number', 'Expenses');
  data.addColumn({type: 'string', role: 'tooltip'});
  data.addRows([
    ['2004', 1000, '1M$ sales in 2004', 400,  '$0.4M expenses in 2004'],
    ['2005', 1170, '1.17M$ sales in 2005', 460, '$0.46M expenses in 2005'],
    ['2006', 660,  '.66$ sales in 2006', 1120, '$1.12M expenses in 2006'],
    ['2007', 1030, '1.03M$ sales in 2007', 540, '$0.54M expenses in 2007']
  ]);

  // Create and draw the visualization.
  new google.visualization.BarChart(document.getElementById('visualization')).
      draw(data,
           {title:"Yearly Coffee Consumption by Country",
            isStacked: true,
            width:600, height:400,
            vAxis: {title: "Year"},
            hAxis: {title: "Sales"}}
      );
}

---

请看一个例子。

我昨天花了几个小时试图弄明白这一点。非常感谢你。