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Question:

I have seen numerous answers on here about creating an intent filter for a custom file extension, but none of them seem to be answering my question:

I have an intent filter that works right now... when I browse for my file or when I open it from an email attachment, my app will appear in the list. The file itself has a custom extension of "tgtp", but it is basically just an xml file.

The problem I am having is that although this intent filter works, it also appears to add my app to every chooser for every type of file on my phone. An example would be if I clear my contacts app defaults and click on one of my contacts, it says my app can open it.

I've tried dozens of different combinations of intent filters with different schemes, mime types, etc... and some still let me open the file if i browse with a file browser, but I specifically need to be able to open email attachments and open as file browser. I am yet to find an intent filter(s) that allow me to do that without making my app available for every other intent chooser.

Here is my current intent-filter that uses my app to open everything:

<intent-filter>
<action android:name="android.intent.action.VIEW" />
<category android:name="android.intent.category.DEFAULT" />
<data android:mimeType="*/*" />
<data android:pathPattern=".*.tgtp" />   
</intent-filter>

Thank you in advance


Best Answer:


I've been struggling with this quite a bit for a custom file extension, myself. After a lot of searching, I found this web page where the poster discovered that Android's patternMatcher class (which is used for the pathPattern matching in Intent-Filters) has unexpected behavior when your path contains the first character of your match pattern elsewhere in the path (like if you're trying to match "*.xyz", the patternMatcher class stops if there's an "x" earlier in your path). Here's what he found for a workaround, and worked for me, although it is a bit of a hack:

PatternMatcher is used for pathPattern at IntentFilter But, PatternMatcher's algorithm is quite strange to me. Here is algorithm of Android PatternMatcher.

If there is 'next character' of '.*' pattern in the middle of string, PatternMatcher stops loop at that point. (See PatternMatcher.java of Android framework.)

Ex. string : "this is a my attachment" pattern : ".att.". Android PatternMatcher enter loop to match '.' pattern until meet the next character of pattern (at this example, 'a') So, '.' matching loop stops at index 8 - 'a' between 'is' and 'my'. Therefore result of this match returns 'false'.

Quite strange, isn't it. To workaround this - actually reduce possibility - developer should use annoying stupid pathPattern.

Ex. Goal : Matching uri path which includes 'message'.

<intent-filter>
...
<data android:pathPattern=".*message.*" />
<data android:pathPattern=".*m.*message.*" />
<data android:pathPattern=".*m.*m.*message.*" />
<data android:pathPattern=".*m.*m.*m.*message.*" />
<data android:pathPattern=".*m.*m.*m.*m.*message.*" />
...
</intent-filter>

This is especially issued when matching with custom file extention.




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