Base-64 char数组或字符串C＃

Question

字符串长度是4的倍数，所以我不明白为什么会收到此错误。

    private static void SaveImageToFile(string imageString)
    {
        try
        {
            string base64Data = Regex.Replace(imageString, @"\s+", "");
            base64Data = System.Web.HttpUtility.UrlDecode(base64Data.Replace('-', '+').Replace(" ","").Replace('_', '/'));
            if (base64Data.Length % 4 > 0)
                base64Data = base64Data.PadRight(base64Data.Length + 4 - base64Data.Length % 4, '=');
            var length = base64Data.Length;
            var binData = Convert.FromBase64String(base64Data);
        }
        catch (Exception ex) { }
    }

“ base-64字符数组或字符串的长度无效” 错误被抛出FromFrom6464String

这是我传递的字符串： iVBORw0KGgoAAAANSUhEUgAABwgAAAAPCAYAAADwMZuwAAAFW0lEQVR4Xu3d22scZRzG8efd8 + wpu9lNNocebJsEEUsDXnggKI1tU42CeiF4qFYERamlYgsW + J + otQheeeN％2f4IXeeRmoemNPoDWpxXVrc9pkN3uamR3ZSf0jxvkODC9z93s + u3cP7％2fuaVq％2fjbXd2tNas65％2fGxu66va7l1b％2fV7rU1li％2frvadf1sTQiHgQQAABBBBAAAEEEEAAAQQQQAABBBBAAAEEEEAAAQQQQCDYAubbq997rV5Hg5Kw0Wmp2W3560ZzS27f1Vi + pFcfO67RfFEyxk％2fbsbvqOraePHA42OmZHgEEEEAAAQQQQAABBBBAAAEEEEAAAQQQQAABBBBAAIGQCZiXvr7g2Y7tF35uvy + n78p1d99YNKpyZkhzU7Oq5EuKxWJq210NCsWu09Mnz74RMi7iIoAAAggggAACCCCAAAIIIIAAAggggAACCCCAAAIIIBBsAbP41TnPGRSDruMXhINi0BkUhH1XURORFU + qkilqemy％2fRgvDulFbUTZlqZIbpiAM9m％2fP9AgggAACCCCAAAIIIIAAAggggAACCCCAAAIIIIAAAiEUMCevnPWSsYTikah2em2lYknFIzFV6％2fdlu46saEKV7LAeHntIlUJJ1 + 8tK2el％2faNHP55％2fPYRkREYAAQQQQAABBBBAAAEEEEAAAQQQQAABBBBAAAEEEEAguAJm4cpZbyiVUT6V0eCGwYKVU0RGV％2F + 8qWanpUw8panSHs2M7lUpW9DtzaoS8YQKVlbn5l8LbnImRwABBBBAAAEEEEAAAQQQQAABBBBAAAEEEEAAAQQQQCCEAubElx95i​​WhM40NlvfjonGzH0a17K％2frxt1％2fU7LRVSGX0SOWADpUnVUjntLJZk4xRMpnUhWNvhpCMyAgggAACCCCAAAIIIIAAAggggAACCCCAAAIIIIAAAg gEV8Acv3zGixijiaGy3n78Ba0361pauaaf7tz0jxwtpLI6MjGtqZE9KqZzWl6vqS9PyXhc50 + cCm5yJkcAAQQQQAABBBBAAAEEEEAAAQQQQAABBBBAAAEEEEAghALm2OUzXtRENJYf1itHjvoF4c93b + nX6u9q9TrKJzOanZzxjxgtpvP6Y60qT55S8YTOL7wVQjIiI4AAAggggAACCCCAAAIIIIAAAggggAACCCCAAAIIIBBcATP％2fxYfeYGfgeL6sg6UJZRKW6q2GfrixpEZnx7 + bcGZknw6NTPo7CG + v％的2fSVjjNIJS5cW3w1uciZHAAEEEEAAAQQQQAABBBBAAAEEEEAAAQQQQAABBBBAIIQC5ujnH3hWPKlM0pIVSyoViz + 4H％2fCObMf2C8PxfEkzlX0qZwu6VltWOpHUSK6oS89TEIbwP0NkBBBAAAEEEEAAAQQQQAABBBBAAAEEEEAAAQQQQACBAAv4BaHb78vtu3JdV86DdfAdi0SVjlv + 8aPTo3tVyhZ0vbasnJX2S8OLJ98JcHRGRwABBBBAAAEEEEAAAQQQQAABBBBAAAEEEEAAAQQQQCB8AuaZz973 + p7nl4ODUtD5ryTsu0rFEhrNDuupg4f9HYPRSFQtu6uu05Pdd3Rx4XT4xEiMAAIIIIAAAggggAACCCCAAAIIIIAAAggggAACCCCAQIAFzDdL33k73ba22k01Oi1tt5uqt5rabG3Ldh1VckWdemJRY％2fmSPLObtOfY％2fjs3NRvg6IyOAAIIIIAAAggggAACCCCAAAIIIIAAAggggAACCCCAQPgEjOd53mpjU9X6qu43NlTbWlN1c1V3N2pab2759w5 ++ txp7S + Nh0 + HxAgggAACCCCAAAIIIIAAAggggAACCCCAAAIIIIAAAgj8zwT + BRNcWuMhdT3NAAAAAElFTkSuQmCC

function DownloadAsImage() {
    var element = $("#map-container")[0];
    html2canvas(element).then(function (canvas) {
    var myImage = canvas.toDataURL().replace('data:image/png;base64,', 
    '');
    var url = '/umbraco/api/countymap/SaveMapImage';
    $.ajax({            
        url: url,
        data: myImage,
        dataType: 'json',
        type: 'POST',
        processData: false,
        success: function (data) {
            console.log('It worked!');
        }
    });
    //downloadURI(myImage, "map.png");
});

}