Question

我有多个画布元素，它们基于VB代码在我的页面上动态显示。

这就是我的aspx页面：

<canvas id="canvasnhlrc" width="225" height="200" runat="server"></canvas>
<canvas id="canvascwl" width="225" height="200" runat="server"></canvas>
<canvas id="canvashslanguages" width="225" height="200" runat="server"></canvas>

这就是我的aspx.vb代码：

canvasnhlrc.Visible = False
canvascwl.Visible = False
canvashslanguages.Visible = False

        If RouteData.Values("mediasubType") IsNot Nothing Then

            Dim qsubMedia As String = RouteData.Values("mediasubType")

            Select Case qsubMedia

                Case "nhlrc"

                    canvasnhlrc.Visible = True

                Case "cwl"

                    canvascwl.Visible = True

                Case "hslanguages"

                    canvashslanguages.Visible = True

            End Select

        End If

因此，如果我的页面是example.com/nhlrc，那么画布将生成为

<canvas id="ContentPlaceHolder2_canvasnhlrc" width="225" height="200"></canvas>

因此，我将js文件格式化如下：

function init() 
{ 
    var w1 = document.getElementById('ContentPlaceHolder2_canvasnhlrc')
    var w1x = w1.getContext('2d');
    w1x.shadowOffsetX = 0;
    w1x.shadowOffsetY = 0;
    w1x.shadowBlur = 20;
    w1x.shadowColor = "rgba(0, 0, 0, 0.75)";
    w1x.fillStyle = 'rgb(218, 233, 246)';
    w1x.beginPath();
    w1x.moveTo(25, 25);
    w1x.lineTo(175, 25);
    w1x.lineTo(175, 50);
    w1x.lineTo(200, 75);
    w1x.lineTo(175, 100);
    w1x.lineTo(175, 175);
    w1x.lineTo(25, 175);
    w1x.closePath();
    w1x.fill();

    var w2 = document.getElementById('ContentPlaceHolder2_canvascwl')
    var w2x = w2.getContext('2d');
    w2x.shadowOffsetX = 0;
    w2x.shadowOffsetY = 0;
    w2x.shadowBlur = 20;
    w2x.shadowColor = "rgba(0, 0, 0, 0.75)";
    w2x.fillStyle = 'rgb(12, 64, 114)';
    w2x.beginPath();
    w2x.moveTo(25, 25);
    w2x.lineTo(175, 25);
    w2x.lineTo(175, 50);
    w2x.lineTo(200, 75);
    w2x.lineTo(175, 100);
    w2x.lineTo(175, 175);
    w2x.lineTo(25, 175);
    w2x.closePath();
    w2x.fill();

    var w3 = document.getElementById('ContentPlaceHolder2_canvashslanguages')
    var w3x = w3.getContext('2d');
    w3x.shadowOffsetX = 0;
    w3x.shadowOffsetY = 0;
    w3x.shadowBlur = 20;
    w3x.shadowColor = "rgba(0, 0, 0, 0.75)";
    w3x.fillStyle = 'rgb(12, 64, 114)';
    w3x.beginPath();
    w3x.moveTo(25, 25);
    w3x.lineTo(175, 25);
    w3x.lineTo(175, 50);
    w3x.lineTo(200, 75);
    w3x.lineTo(175, 100);
    w3x.lineTo(175, 175);
    w3x.lineTo(25, 175);
    w3x.closePath();
    w3x.fill();
}
onload = init;

可悲的是，我只能显示第一个画布元素（NHLRC），而后续的画布（example.com/cwl等）不会渲染。代码没有任何问题，因为当我在JS代码中注释掉其他两个元素时，它工作得很好，所以我错过了什么，做错了什么，或者是什么相互冲突，不允许每一个要在相应页面中渲染的画布元素？

Answer 1

您的初始化函数有太多责任（查找，验证和绘制）* 3。当这些责任中的任何一个遇到失败，即找不到元素时，节目就会停止。在您的情况下，w1, w2, w3只会在各自的页面中定义，而不是在每个页面中定义。

您可以将其简化如下：

function draw(theCanvasEl, theFill) 
{ 
    var w1x = theCanvasEl.getContext('2d');
    w1x.shadowOffsetX = 0;
    w1x.shadowOffsetY = 0;
    w1x.shadowBlur = 20;
    w1x.shadowColor = "rgba(0, 0, 0, 0.75)";
    w1x.fillStyle = theFill;
    w1x.beginPath();
    w1x.moveTo(25, 25);
    w1x.lineTo(175, 25);
    w1x.lineTo(175, 50);
    w1x.lineTo(200, 75);
    w1x.lineTo(175, 100);
    w1x.lineTo(175, 175);
    w1x.lineTo(25, 175);
    w1x.closePath();
    w1x.fill();
}

function init()
{
  var canvases = [['ContentPlaceHolder2_canvasnhlrc', 'rgb(218, 233, 246)'],
     ['ContentPlaceHolder2_canvascwl', 'rgb(12, 64, 114)'],
     ['ContentPlaceHolder2_canvashslanguages', 'rgb(12, 64, 114)']];

   for(var i=0;i<canvases.length;i++)
   { 
       var theCanvas = document.getElementById(canvases[i][0]);
       if (theCanvas!=null) {
         draw(theCanvas, canvases[i][1]);
         break;              
       }
   }
}

onload = init;

ASP.NET中动态生成的画布元素

1 个答案: