Xamarin.Forms WebView选文件抛出ClassCastException异常求助

问题原因 #

你使用的mUploadCallbackAboveL是Android 5.0+的IValueCallback<Uri[]>类型，它的OnReceiveValue方法要求传入Uri数组，但你直接传入了单个Uri对象，触发类型转换异常。

修复代码 #

修改OnActivityResult方法，将单个Uri包装成数组传入：

protected override void OnActivityResult(int requestCode, Result resultCode, Intent intent)
{
    if (requestCode == FILECHOOSER_RESULTCODE)
    {
        if (null == mUploadCallbackAboveL)
            return;

        Uri[] results = null;
        if (resultCode == Result.Ok && intent != null)
        {
            // 将单个Uri包装为数组
            results = new Uri[] { intent.Data };
        }

        // 传入Uri数组，取消选择时传入null
        mUploadCallbackAboveL.OnReceiveValue(results);
        mUploadCallbackAboveL = null;
    }
}

额外适配（支持多选文件） #

如果你的HTML文件输入框设置了multiple属性支持多选，需要处理Intent返回的多个Uri：

protected override void OnActivityResult(int requestCode, Result resultCode, Intent intent)
{
    if (requestCode == FILECHOOSER_RESULTCODE)
    {
        if (null == mUploadCallbackAboveL)
            return;

        Uri[] results = null;
        if (resultCode == Result.Ok && intent != null)
        {
            if (intent.ClipData != null)
            {
                // 处理多选文件
                int count = intent.ClipData.ItemCount;
                results = new Uri[count];
                for (int i = 0; i < count; i++)
                {
                    results[i] = intent.ClipData.GetItemAt(i).Uri;
                }
            }
            else
            {
                // 处理单个文件
                results = new Uri[] { intent.Data };
            }
        }

        mUploadCallbackAboveL.OnReceiveValue(results);
        mUploadCallbackAboveL = null;
    }
}

内容的提问来源于stack exchange，提问作者KuroCoder