使用本地属性和文件位置将图像添加到光开关

最近解决了类似的情况,我们实现了以下helper promise操作函数:-

function GetImageProperty (operation) {
    var image = new Image();
    var canvas = document.createElement("canvas");
    var ctx = canvas.getContext("2d");
    // XMLHttpRequest used to allow external cross-domain resources to be processed using the canvas.  
    // unlike crossOrigin = "Anonymous", XMLHttpRequest works in IE10 (important for LightSwitch) 
    // still requires the appropriate server-side ACAO header (see https://developer.mozilla.org/en-US/docs/Web/HTML/CORS_enabled_image)
    var xhr = new XMLHttpRequest();
    xhr.onload = function () {
        var url = URL.createObjectURL(this.response);
        image.onload = function () {
            URL.revokeObjectURL(url);
            canvas.width = image.width;
            canvas.height = image.height;
            ctx.drawImage(image, 0, 0);
            var dataURL = canvas.toDataURL("image/png");
            operation.complete(dataURL.substring(dataURL.indexOf(",") + 1));
        };
        image.src = url;
    };
    xhr.open('GET', this.imageSource, true);
    xhr.responseType = 'blob';
    xhr.send();
};

添加了一个本地属性(添加数据项->本地属性->类型:图像->,名称:图像属性)并将其放置到内容项树中后,promise操作可以在_postRender例程中以以下方式执行:-

msls.promiseOperation
(
    $.proxy(
        GetImageProperty,
        { imageSource: "content/images/user-splash-screen.png" }
    )
).then(
    function (result) { 
        contentItem.screen.ImageProperty = result; 
    }
);

或者,它可以在屏幕的创建函数中调用如下:-

msls.promiseOperation
(
    $.proxy(
        GetImageProperty,
        { imageSource: "https://s3-us-west-2.amazonaws.com/s.cdpn.io/3/pie.png" }
    )
).then(
    function (result) { 
        screen.ImageProperty = result; 
    }
);

上述调用还表明,除了显示LightSwitch项目的本地图像外,还可以将imageSource设置为外部url(前提是外部站点使用适当的服务器端ACAO标头以允许跨域访问)。

编辑:我已经更新了这个助手函数,以稍微改进它,以回应这篇文章 Adding static image to Lightswitch HTML 2013 Browse Screen .