iPhone应用程序在QLPreviewController ios 4.2中点击菜单操作按钮时崩溃

 When I try to click the menu action button in QLPreviewController the application crashes.

这就是我在委托方法中所做的事情

This is what I'm doing in delegate method

- (id)previewController:(QLPreviewController *)previewController previewItemAtIndex:(NSInteger)index
{

    NSMutableString*Url = [[NSMutableString alloc] initWithFormat:@"http://10.30.24.21/Documents/abc.doc];

    NSURL *fileURL;
    fileURL = [NSURL URLWithString:Url];// the url of the file which is present in NAS device
    [Url release];
    return fileURL;
}

这是崩溃报告

2011-01-11 12:21:36.717 iLink[5548:207] *** Assertion failure in -[UIDocumentInteractionController setURL:], /SourceCache/UIKit_Sim/UIKit-1447.6.4/UIDocumentInteractionController.m:1060
2011-01-11 12:21:36.720 iLink[5548:207] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'UIDocumentInteractionController: invalid scheme https.  Only the file scheme is supported.'

当我尝试预览文件时，本地菜单操作按钮点击不会崩溃。

When I try to preview file present locally menu action button click is not crashing.

我将使用

 NSURL *fileURL;
    fileURL = [NSURL fileURLWithPath:filePath];// filePath is local file path.

据我所知，当我们预览本地文件（[NSURL fileURLWithPath：filePath]）时，菜单操作按钮点击是没有崩溃，当我们从服务器预览文件时（[NSURL URLWithString：Url]）菜单操作按钮点击崩溃。

I understood that when we preview local files ([NSURL fileURLWithPath:filePath]) menu action button click is not crashing ,, when we preview files from server ([NSURL URLWithString:Url]) menu action button click crashes.

我有两个问题，
1。我们可以禁用菜单操作按钮吗？
2.有没有办法使用[NSURL URLWithString：Url]来避免崩溃？

I have two questions, 1. Can we disable the menu action button? 2. Is there any way to avoid the crash using [NSURL URLWithString:Url]?

谢谢