cocos creator 计算文字宽度

var rank = new cc.Node()

            var rankLabel = rank.addComponent(cc.Label)

            rankLabel.string = "排名上升"

            rankLabel.fontSize = 30

            rankLabel.verticalAlign = "CENTER"

            var rankOutline = rank.addComponent(cc.LabelOutline);

            rankOutline.color = new cc.color(0,0,0,255)

            rankOutline.width = 2

            rankLabel._forceUpdateRenderData(true);

            rank.position = cc.p(-txtWidth+rank.width/2,0)

            rank.parent = this.box