在Android Cordova上将内容从文件///移动到内容///(xapk/obb）后，Canvas.toDataU

我在Cordova 5.4.1中使用以下插件：

• 白名单插件
• XAPKReader

index.html标题包括这个CSP元标签（不得不丑化谷歌TalkBack URL）：

<meta http-equiv="Content-Security-Policy" 
    content="default-src 'self' 'unsafe-inline' 'unsafe-eval' 
      data: gap: content: cdvfile: ....google-URLS...; 
    img-src data: gap: file: content: cdvfile: ....google-URLS...; 
    style-src 'self' 'unsafe-inline'; script-src 'self' 'unsafe-inline' 'unsafe-eval'; 
    connect-src 'self' ....google-URLS..." />

config.xml包括：

<allow-navigation href="http://*/*" />
<access origin="*://*" />
<allow-intent href="content://*" />
<allow-intent href="content://*/*/*/*" />

当画布显示具有文件///*URL的图像，但不具有类似URLS的内容///*时，我的画布相关代码看起来是这样的，并且运行良好

html2canvas($("#layerA"), {onrendered:function(stageCanvas){
    var stageCtx = stageCanvas.getContext('2d');
    var tmpCanvas = document.createElement('canvas');
        tmpCanvas.width = stageCanvas.width;
        tmpCanvas.height = stageCanvas.height;
    var tmpCtx = stageCanvas.getContext('2d');
    var imgObj = new Image();
    imgObj.onload = function(){
        var destX = 0;
        var destY = 0;
        tmpCtx.drawImage(imgObj,
            sourceX, sourceY, sourceWidth, sourceHeight,
            0, 0, destWidth, destHeight);
        var data = tmpCtx.getImageData(sourceX, sourceY, sourceWidth, sourceHeight);
        stageCtx.clearRect(0, 0, stageCanvas.width, stageCanvas.height); //clear originalCanvas
        stageCanvas.width = sourceWidth;
        stageCanvas.height = sourceHeight;
        tmpCtx.putImageData(data,0,0);
        var datauri = null;
        try {
            datauri = stageCanvas.toDataURL('image/png');
        } catch(err) {
            alert(err);
        }
        // store the image and update UI
        $('#fav-img-'+maxFavUsed.toString()).attr('src', datauri);
        $("#fav-del-"+maxFavUsed.toString()).show();
        $('#fav-big').attr('src', datauri);
        if(typeof(Storage) !== "undefined") {
            localStorage.setItem('fav-img-'+maxFavUsed.toString(), datauri);
        }
        showFav(maxFavUsed);
        showUI();
        //clear memory!!!
        stageCtx.clearRect(0, 0,  sourceWidth, sourceHeight);//clear originalCanvas
        tmpCtx.clearRect(0, 0, sourceWidth, sourceHeight);//clear tmpCanvas
        data = null;
        datauri = null;
        tmpCanvas = null;
        stageCanvas = null;
        imgObj = null;
    };
    try {
        imgObj.src = tmpCanvas.toDataURL("image/png");
    } catch(err) {
        alert(err);
    }
}, width:canvasW, height:canvasH } );

上面的代码不会抛出也不会发出警报，但会创建空的datauri，所以我认为画布受到了CORS问题的影响。以content://开头的URL由XAPKReader插件附带的java类ContentProvider提供服务。