我已经查看了所有类似的问题在这里，但我不能为我的生命找出我做错了。

I've reviewed all the similar questions here, but I can't for the life of me figure out what I'm doing wrong.

我已经写了一种尝试推出各种文件，排序文件浏览器应用程序。 当点击一个文件，它会尝试推出基于其关联的MIME类型的程序或presents选择应用程序启动对话框。

I've written an application that tries to launch various files, sort of a file browser. When a file is clicked, it tries to launch the program based on its associated MIME type or it presents the "Choose Application to Launch" dialog.

这里的code我使用启动：

Here's the code I'm using to launch:

    File file = new File(app.mediaPath() + "/" +_mediaFiles.get(position));

    Intent myIntent = new Intent(android.content.Intent.ACTION_VIEW);

    String extension = android.webkit.MimeTypeMap.getFileExtensionFromUrl(Uri.fromFile(file).toString());
    String mimetype = android.webkit.MimeTypeMap.getSingleton().getMimeTypeFromExtension(extension);
    myIntent.setDataAndType(Uri.fromFile(file),mimetype);
    startActivity(myIntent);

此失败并生成错误：

android.content.ActivityNotFoundException: No Activity found to handle Intent { act=android.intent.action.VIEW dat=file:///file:/mnt/sdcard/roms/nes/Baseball_simulator.nes }

现在，如果我装OI文件管理器，例如，它会打开，而不是这个错误被抛出，然后如果我从内它，它会启动选择恰当的对话框中单击相同的文件。

Now if I install OI File Manager for instance, it opens instead of this error being thrown, and then if I click the same file from within in it, it launches the approriate dialogs.

我已经注意到，MIME类型特定的文件失败，但像的.zip 其他MIME类型做返回值。

I have noticed that the MIME type for that particular file fails, but other mime types like .zip do return values.

我缺少的东西，当MIME类型为null调用一个对话框，让用户选择？

Am I missing something that when the MIME type is null to call a dialog that lets the user select?

我试着启动应用程序，包括不设置MIME类型，只使用 .setData 没有成功的其他变化。

    File file = new File(filePath);
    MimeTypeMap map = MimeTypeMap.getSingleton();
    String ext = MimeTypeMap.getFileExtensionFromUrl(file.getName());
    String type = map.getMimeTypeFromExtension(ext);

    if (type == null)
        type = "*/*";

    Intent intent = new Intent(Intent.ACTION_VIEW);
    Uri data = Uri.fromFile(file);

    intent.setDataAndType(data, type);

    startActivity(intent);