//填充画布,五位随机数

    drawNumber(): void {

        this.clearCanvas();

        let ctx: CanvasRenderingContext2D = this.myGraph.nativeElement.getContext("2d");

        ctx.shadowBlur = 200;

        ctx.shadowColor = "black";

        ctx.font = "italic 20px Verdana";

        ctx.textAlign = "left";

        var gradient = ctx.createLinearGradient(0, 0, this.myGraph.nativeElement.width, 0);

        gradient.addColorStop(0, "magenta");

        gradient.addColorStop(0.5, "blue");

        gradient.addColorStop(1.0, "red");

        ctx.strokeStyle = gradient;

var num = Math.random().toFixed(5) + "";
 this.validateCode = num.slice(2)
 ctx.strokeText(this.validateCode, 3, 22);

}

//清空画布

    clearCanvas(): void {

        let ctx: CanvasRenderingContext2D = this.myGraph.nativeElement.getContext("2d");

        ctx.clearRect(0, 0, this.myGraph.nativeElement.width, this.myGraph.nativeElement.height);

    }