Why usbManager.getAcccessoryList(); always returns null?

Question

I am testing my app in Samsung Galaxy S2 with Android 2.3.4

I am following

http://developer.android.com/guide/topics/usb/accessory.html

instructions.

When ever I try to run it, usbManager.getAcccessoryList(); giving null.

Even I tried by connecting OTG cabel and pendrive to it.

My manifest.

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.test"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-feature android:name="android.hardware.usb.accessory" />

    <uses-sdk android:minSdkVersion="10" />

    <application
        android:icon="@drawable/icon"
        android:label="@string/app_name" >
        <uses-library android:name="com.android.future.usb.accessory" />

        <activity
            android:name=".SplashScreen"
            android:clearTaskOnLaunch="true"
            android:label="@string/app_name"
            android:screenOrientation="portrait" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity
            android:name=".Advanced"
            android:label="@string/app_name"
            android:screenOrientation="portrait" >
        </activity>
        <activity
            android:name=".Edit"
            android:label="@string/app_name"
            android:screenOrientation="portrait" >
        </activity>
        <activity
            android:name=".Add"
            android:label="@string/app_name"
            android:screenOrientation="portrait" >
        </activity>
        <activity
            android:name="Main"
            android:screenOrientation="portrait" >
            <intent-filter>
                <action android:name="android.hardware.usb.action.USB_ACCESSORY_ATTACHED" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>

            <meta-data
                android:name="android.hardware.usb.action.USB_ACCESSORY_ATTACHED"
                android:resource="@xml/accessory_filter" />
        </activity>
    </application>

</manifest>

Answer 1

A cite from http://developer.android.com/guide/topics/usb/accessory.html: "Set the minimum SDK of the application to API Level 10 if you are using the add-on library or 12 if you are using the android.hardware.usb package." You are using the android.hardware.usb package. So, you have to put the version to 12.

An error is found :-)

And don't forget to really change SDK version to 12, not only declare it!

Use com.android.future.usb package instead, according to docs.

Answer 2

I had the same problem but my tablet has ICS. If try what I did, might work. I've been searching a lot for this, and couldn't find it, but thanks to all the people who have spent a few moments answering our questions, and the wiki resources on the web, I figured it out.

There are some missing files in some android builds, like the AINOL NOVO 7 PALADIN. I think this would work in any ICS tablet with the same issue. I understand that the Galaxy Tab has the same issue but as I don't have one I can't confirm this. If you do, let me know if it works for you.

So lets push the files in and see how it goes.

Copy some missing files into system drive:

$ adb remount

$ adb push AINOL_FIX/system/etc/permissions/android.hardware.usb.host.xml /system/etc/permissions

$ adb push AINOL_FIX/system/etc/permissions/android.hardware.usb.accessory.xml /system/etc/permissions

NOTE: If an error appears displaying Out of Memory, it's right and you must delete some files from system drive. I recommend some live wallpapers from system/app.

I understand that for writing system drive you should have root access, I already had it when I did this so if it doesn't work, root it.

You can get the files from android source builds or from a tablet where USB-HOST API is actually working. I got them from linaro's ICS build for pandaboard.

Now, you should try finding those files but for Gingerbread and you'll also need to push the future.usb.accesory.jar into system/framework, if it isn't there already.

$ adb push AINOL_FIX/system/framework/com.android.future.usb.accessory.jar /system/framework