Develop Reference

How to replace FileObserver in Android 10?

android.os.FileObserver requires a java.io.File to function.
But with Android 10 Google restricted access to everything but your app's private directory due to the famous "Storage Access Framework". Thus, accessing anything via java.io.File breaks and renders FileObserver useless unless you intend to use it in your app's private directory. However, I want to be notified when something is changed in a certain directory on external storage. I would also like to avoid periodically checking for changes.
I tried using ContentResolver.registerContentObserver(uri,notifyForDescendants,observer) and ran into some problems with that method:
Every Uri I have plugged in so far was accepted
It neither fails nor notifies if the Uri doesn't work
I cannot find any documentation telling me which Uris actually work
The only thing I got working to some extent is the following approach:
// works, but returns all changes to the external storage
contentResolver.registerContentObserver(MediaStore.Files.getContentUri("external"), true, contentObserver)
Unfortunately this includes all of the external storage and only returns Media Uris when changes happen - for example content://media/external/file/67226.
Is there a way to find out whether or not that Uri points to my directory?
Or is there a way to make registerContentObserver() work with a Uri in such a way that I get a notification whenever something in the folder has changed?
I also had no success trying various Uris related to DocumentsFile and external storage Uris.

I kept getting errors when even trying to use the base constructor such as the following -
No direct method <init>(Ljava/util/List;I)V in class Landroid/os/FileObserver; or its super classes (declaration of 'android.os.FileObserver' appears in /system/framework/framework.jar!classes2.dex)
From a comment on Detect file change using FileObserver on Android:
I saw that message (or something like that) when i was trying to use constructor FileObserver(File). Use of deprecated FileObserver(String) solved my problem.... Original FileObserver has bugs.
Full disclosure, I was using the Xamarin.Android API; however, the gist and the commenter I quoted were both working with Java. At any rate, indeed - tried again using the counterpart String constructor and I was finally able to make and use the observer. Grinds my gears to use a deprecated API, but apparently they're hanging onto it at least up to and including Android 12.0.0_r3... still, would much prefer the supported constructors actually work. Maybe there's some warrant here for filing an issue.

I found a way to implement FileObserver on Android 10 with ContentObserver, but it might only work with media files since it works with media content uris.
The uri for ContentResolver.registerContentObserver() should be the file's corresponding media uri (e.g. content://media/external/file/49) which is queried by file path.
fun getMediaUri(context: Context, file: File): Uri? {
val externalUri = MediaStore.Files.getContentUri("external")
context.contentResolver.query(
externalUri,
null,
"${MediaStore.Files.FileColumns.DATA} = ?",
arrayOf(file.path),
null
)?.use { cursor ->
if (cursor.moveToFirst()) {
val idIndex = cursor.getColumnIndex("_id")
val id = cursor.getLong(idIndex)
return Uri.withAppendedPath(externalUri, "$id")
}
}
return null
}
Then ContentObserver.onChange() will be triggered for every file change with uri: content://media/external/file/{id}; uri in ContentObserver.onChange(boolean selfChange, Uri uri) will always be content://media/external/file; only registered file will be with id (e.g. content://media/external/file/49?deletedata=false).
Does what FileObserver used to do when input uri's path matches registered uri.

I have a temporary solution for this issue, so let's see if this can help.
I start an infinite while loop watching for file created and file deleted (if you want file modified or file renamed you have to implement more) using DocumentFile. Below is my sample:
private static int currentFileIndirectory = 0;
private static final int FILE_CREATED = 0;
private static final int FILE_DELETED = 1;
private static DocumentFile[] onDirectoryChanged(DocumentFile[] documentFiles, int event) {
Log.d("FileUtil", "onDirectoryChanged: " + event);
if (event == FILE_CREATED) {
} else {
}
return documentFiles;
}
private static boolean didStartWatching = false;
private static void startWatchingDirectory(final DocumentFile directory) {
if (!didStartWatching) {
didStartWatching = true;
DocumentFile[] documentFiles = directory.listFiles();
if (null != documentFiles && documentFiles.length > 0) {
currentFileIndirectory = documentFiles.length;
}
new Thread(new Runnable() {
public void run() {
while (true) {
DocumentFile[] documentFiles = directory.listFiles();
if (null != documentFiles && documentFiles.length > 0) {
if (documentFiles.length != currentFileIndirectory) {
if (documentFiles.length > currentFileIndirectory) {//file created
DocumentFile[] newFiles = new DocumentFile[documentFiles.length - currentFileIndirectory];
onDirectoryChanged(newFiles, FILE_CREATED);
} else {//file Deleted
onDirectoryChanged(null, FILE_DELETED);
}
currentFileIndirectory = documentFiles.length;
}
}
}
}
}).start();
}
}

How to load image (icons) of apps faster in gridView?

I am displaying all apps installed in a gridView. When loading a lot of apps, lets say 30 or more, the icons will display at the default Android icon and then several seconds later update to the correct icon. I am wondering about improvements I can make to my code to make the icon images display faster.
Load the following with: new LoadIconsTask().execute(mApps.toArray(new AppsInstalled[]{}));
Here is what I do.
private class LoadIconsTask extends AsyncTask<AppsInstalled, Void, Void>{
#Override
protected Void doInBackground(AppsInstalled... params) {
// TODO Auto-generated method stub
Map<String, Drawable> icons = new HashMap<String, Drawable>();
PackageManager manager = getApplicationContext().getPackageManager();
// match package name with icon, set Adapter with loaded Map
for (AppsInstalled app : params) {
String pkgName = app.getAppUniqueId();
Drawable ico = null;
try {
Intent i = manager.getLaunchIntentForPackage(pkgName);
if (i != null) {
ico = manager.getActivityIcon(i);
}
} catch (NameNotFoundException e) {
Log.e(TAG, "Unable to find icon match based on package: " + pkgName
+ " : " + e.getMessage());
}
icons.put(app.getAppUniqueId(), ico);
}
mAdapter.setIcons(icons);
return null;
}
Also populate my listing of apps before I loadIconsTask() with
private List<App> loadInstalledApps(boolean includeSysApps) {
List<App> apps = new ArrayList<App>();
// the package manager contains the information about all installed apps
PackageManager packageManager = getPackageManager();
List<PackageInfo> packs = packageManager.getInstalledPackages(0); // PackageManager.GET_META_DATA
for (int i = 0; i < packs.size(); i++) {
PackageInfo p = packs.get(i);
ApplicationInfo a = p.applicationInfo;
// skip system apps if they shall not be included
if ((!includeSysApps)
&& ((a.flags & ApplicationInfo.FLAG_SYSTEM) == 1)) {
continue;
}
App app = new App();
app.setTitle(p.applicationInfo.loadLabel(packageManager).toString());
app.setPackageName(p.packageName);
app.setVersionName(p.versionName);
app.setVersionCode(p.versionCode);
CharSequence description = p.applicationInfo
.loadDescription(packageManager);
app.setDescription(description != null ? description.toString()
: "");
apps.add(app);
}
return apps;
}
In regards to my Adapter class it is standard. My getView() looks like the following:
#Override
public View getView(int position, View convertView, ViewGroup parent) {
AppViewHolder holder;
if (convertView == null) {
convertView = mInflater.inflate(R.layout.row, null);
// creates a ViewHolder and stores a reference to the children view
// we want to bind data to
holder = new AppViewHolder();
holder.mTitle = (TextView) convertView.findViewById(R.id.apptitle);
holder.mIcon = (ImageView) convertView.findViewById(R.id.appicon);
convertView.setTag(holder);
} else {
// reuse/overwrite the view passed assuming that it is castable!
holder = (AppViewHolder) convertView.getTag();
}
App app = mApps.get(position);
holder.setTitle(app.getTitle());
if (mIcons == null || mIcons.get(app.getPackageName()) == null) {
holder.setIcon(mStdImg);
} else {
holder.setIcon(mIcons.get(app.getPackageName()));
}
return convertView;
}
Is there a better way? Can I somehow store the images of the icons in a data structure and when I return back to this Activity I can skip the loadIconsTask? Is that possible? Thank you in advance.

You can use Picasso library with a custom RequestHandler to load the icons in the background.
First create a RequestHandler which will handle the specific case where an app icon needs to be loaded.
public class AppIconRequestHandler extends RequestHandler {
/** Uri scheme for app icons */
public static final String SCHEME_APP_ICON = "app-icon";
private PackageManager mPackageManager;
public AppIconRequestHandler(Context context) {
mPackageManager = context.getPackageManager();
}
/**
* Create an Uri that can be handled by this RequestHandler based on the package name
*/
public static Uri getUri(String packageName) {
return Uri.fromParts(SCHEME_APP_ICON, packageName, null);
}
#Override
public boolean canHandleRequest(Request data) {
// only handle Uris matching our scheme
return (SCHEME_APP_ICON.equals(data.uri.getScheme()));
}
#Override
public Result load(Request request, int networkPolicy) throws IOException {
String packageName = request.uri.getSchemeSpecificPart();
Drawable drawable;
try {
drawable = mPackageManager.getApplicationIcon(packageName);
} catch (PackageManager.NameNotFoundException ignored) {
return null;
}
Bitmap bitmap = ((BitmapDrawable) drawable).getBitmap();
return new Result(bitmap, Picasso.LoadedFrom.DISK);
}
}
In your adapter, create a Picasso instance and add your RequestHandler.
// field variable
private Picasso mPicasso;
// in constructor
Picasso.Builder builder = new Picasso.Builder(context);
builder.addRequestHandler(new AppIconRequestHandler(context));
mPicasso = builder.build();
In your adapter's getView() load the icon using Picasso.
mPicasso.load(AppIconRequestHandler.getUri(app.packageName)).into(holder.mIcon);

it's surprising the system takes that much time in getting these lists, you may want to add some logs with timestamping to see which one is the demanding operation.
I don't know if that procedure can be further optimized, I haven't used these system API's very much, but what you can certainly do is to cache this list
Create it in onResume / onCreate as a static list, and (for the sake of correctness) destroy it in onPause / onStop if you want to consider the case where the user may install an application while in your app (onPause will be called), but you can certainly skip this step.
You may want to also permanently cache the list in the sdcard and find some simple and fast heuristic to decide if the list has changed in order to recreate it. Something like maybe the number of installed packages together with something else (to discard the case when the user uninstalls 3 apps and install 3 different apps, the number of packages will be the same and you have to detect this somehow).
EDIT- To recommend a caching mechanism, you should identify which one is the slow operation. Just guessing, and from your question "the icons take some seconds to appear" it looks like that the slow operation is:
ico = manager.getActivityIcon(i);
but I might be wrong. Let's suppose I'm right, so a cheap caching can be:
1) Move the Map<String, Drawable> icons = new HashMap<String, Drawable>(); outside of doInBackground to the root of the class and make it static, like:
private static Map<String, Drawable> sIcons = new HashMap<String, Drawable>()
2) In your loadIconsTask consider the case you already have this icon:
for (AppsInstalled app : params) {
String pkgName = app.getAppUniqueId();
if (sIcons.containsKey(pkgName) continue;
.
.
.
}
This is because sIcons is now static and will be alive as long as your application is alive.
3) As a classy thing, you may want to change sIcons from Drawable to Bitmap. Why? Because a Drawable may keep inside references to Views and Context and it's a potential memory leak. You can get the Bitmap from a Drawable very easily, calling drawable.getBitmap() , (Assuming drawable is a BitmapDrawable, but it will obviously be because it's an app icon), so suming up you'll have:
// the static icon dictionary now stores Bitmaps
static Map<String, Bitmap> sIcons = new HashMap<String, Bitmap>();
.
.
// we store the bitmap instead of the drawable
sIcons.put(app.getAppUniqueId(), ((BitmapDrawable)ico).getBitmap());
.
.
// when setting the icon, we create the drawable back
holder.setIcon(new BitmapDrawable(mIcons.get(app.getPackageName())));
This way your static hashmap will never leak any memory.
4) You may want to check if it's worth to store those bitmaps on disk. Mind this is some additional work and it might not be worth if the time to load the icon from disk is similar to the time to load the icon calling ico = manager.getActivityIcon(i);. It may be (i don't know if manager.getActivityIcon() extracts the icon from the APK) but it certainly may be not.
If you check out it's worth, when you create the list, you can save the bitmaps to the sdcard like this:
// prepare a file to the application cache dir.
File cachedFile=new File(context.getCacheDir(), "icon-"+app.getPackageName());
// save our bitmap as a compressed JPEG with the package name as filename
myBitmap.compress(CompressFormat.JPEG, quality, new FileOutputStream(cachedFile);
... then when loading the icons, check if the icon exists and load from the sdcard instead:
String key=app.getPackageName();
File localFile=new File(context.getCacheDir(), "icon-"+key);
if (localFile.exists()) {
// the file exists in the sdcard, just load it
Bitmap myBitmap = BitmapFactory.decodeStream(new FileInputStream(localFile));
// we have our bitmap from the sdcard !! Let's put it into our HashMap
sIcons.put(key, myBitmap)
} else {
// use the slow method
}
Well as you see it's just a matter of identifying the slow operation. If our above assumption is correct, your stored bitmaps will survive your application destroy and it will hopefully optimize the icon loading.

You can use Glide for automatic loading and caching and the URI of each application icon:
final RequestManager mGlide = Glide.with(activity);
final Uri appIconUri = applicationInfo.icon != 0 ?
Uri.parse("android.resource://" + packageName + "/" + applicationInfo.icon) :
null;
if (appIconUri != null) mGlide.load(appIconUri).into(holder.appIconImgView);
else {
mGlide.clear(holder.appIconImgView); // as suggested here: https://bumptech.github.io/glide/doc/getting-started.html
mGlide.load(android.R.drawable.sym_def_app_icon).into(holder.appIconImgView);
}
The reason I suggest Glide and not other image loading libraries is that Glide supports XML drawable (or dynamic/adaptive or vector icons) loading while others don't (see https://github.com/facebook/fresco/issues/2173)

How can I load an image from a url into an android remote view for a widget

I have an image url I parse form json that I want to load into an android widget onto the homescreen. Right now I am trying to do it this way but its wrong:
ImageDownloadTask imageD = new ImageDownloadTask(image);
views.setImageViewBitmap(R.id.image, imageD.execute(image));
image is a string holding a url to an image that needs to be downloaded and I am trying to set it to R.id.image
I found another stack question and tried this as a result:
views.setBitmap(R.id.image, "setImageBitmap",BitmapFactory.decodeStream(new URL(image).openStream()));
And when I use that nothing in the app loads at all, none of the text views get set.
My third try was this:
//get beer data
JSONObject o = new JSONObject(result);
String name = getName(o);
String image = getImage(o);
String abv = getABV(o);
String ibu = getIBU(o);
String glass = getGlass(o);
String beerBreweryName = getBreweryName(o);
String beerBreweryStyle = getBreweryStyle(o);
String beerDescription = getDescription(o);
InputStream in = new java.net.URL(image).openStream();
Bitmap bitmap = BitmapFactory.decodeStream(in);
views.setTextViewText(R.id.beerTitle, name);
views.setTextViewText(R.id.beerBreweryName, beerBreweryName);
views.setTextViewText(R.id.beerStyleName, beerBreweryStyle);
views.setImageViewBitmap(R.id.image, bitmap);
This gave the same result as the last attempt, it would not even set any text views....
Just tried another attempt after one of the answers posted below:
RemoteViews views = new RemoteViews(c.getPackageName(), R.layout.widget_test);
//get beer data
JSONObject o = new JSONObject(result);
String name = getName(o);
String imageURL = getImage(o);
String abv = getABV(o);
String ibu = getIBU(o);
String glass = getGlass(o);
String beerBreweryName = getBreweryName(o);
String beerBreweryStyle = getBreweryStyle(o);
String beerDescription = getDescription(o);
Log.d("widgetImage" , imageURL);
views.setImageViewUri(R.id.image, Uri.parse(imageURL));
views.setTextViewText(R.id.beerTitle, name);
views.setTextViewText(R.id.beerBreweryName, beerBreweryName);
views.setTextViewText(R.id.beerStyleName, beerBreweryStyle);
mgr.updateAppWidget(appWidgetIds, views);
This attempt lets all the text views load, but no image ever shows up.

The way to do this reliably is to use setImageViewURI on the remote ImageView. The trick is that the URI you give it is a content:// URI which then points back to a content provider that you export from your application. In your content provider you can do anything you need to do to supply the image bytes.
For example, in your manifest:
<provider android:name=".ImageContentProvider" android:authorities="com.example.test" android:exported="true" />
And your provider:
public class ImageContentProvider extends ContentProvider {
// (Removed overrides that do nothing)
#Override
public ParcelFileDescriptor openFile(Uri uri, String mode) throws FileNotFoundException {
List<String> segs = uri.getPathSegments();
// Download the image content here, get the info you need from segs
return ParcelFileDescriptor.open(new File(path), ParcelFileDescriptor.MODE_READ_ONLY);
}
}
And then your URL is something like:
content://com.example.test/something-you-can-define/here
This is necessary because your remote image view is not running in your process. You are much more limited in what you can do because everything must be serialized across the process boundary. The URI can serialize just fine but if you try to send a megabyte of image data with setImageViewBitmap, it's probably going to fail (depending on available device memory).

Got a lot of help from multiple sources for this question. The big problem for me why a bunch of the attempts I tried listed above seemed to lock the widget app and not load anything is because I can not download the image and set it in a UI thread.
To accomplish this I had to move everything to the do in background of my async task and not in the onPostExecute.

Uri.toString() returns a reference instead of the String

When attempting to execute this code in an Android Activity:
Uri testurl = Uri.parse("http://www.google.com");
Log.v("HTTPGet", "testurl.toString == " + testurl.toString());
the only output in Logcat is a reference to a string, but not the string itself:
HTTPGet(23045): testurl.toString == [Landroid.net.Uri;#4056e398
How can I print the actual string?

ORIGINAL ANSWER (Scratch it)
Uri.toString writes out a description of the URI object from the class Uri.
Documentation is here: http://developer.android.com/reference/android/net/Uri.html
To get the human readable version, invoke the getter methods defined for the class.
THE REAL ANSWER
The OP has clarified and provided the actual code. Here is the actual context:
#Override
protected Document doInBackground(Uri... arg0) {
Document ret = null;
Log.v("HTTPGet", "Uri.toString == " + arg0.toString());
try {
ret = Jsoup.connect(arg0.toString()).get();
} catch (IOException e) {
e.printStackTrace();
}
return ret;
}
What is happening here is that the parameter arg0 has type Uri[], namely an array of Uri. The dot-dot-dot syntax is Java's "varargs". It means the parameter is actually an array, but rather than passing an array in the call, you can pass any number of arguments that Java will bundle up into an array.
Because you are using a third party library, you have to override this method which takes in one or more Uris. You are assuming that only one will be used. If this is the case, you should instead write
Log.v("HTTPGet", "Uri.toString == " + arg0[0].toString());
If you really will be processing multiple uris, use a for-loop to go through and log all of them.
Make sure to fix your Jsoup.connect line too. It doesn't want a messy array string. :)

Invoke getEncodedPath() on Uri to get the string in it.
Something like below
// imageUri is an Uri extracted from Intent
String filePath = imageUri.getEncodedPath();
This filePath will have string content as defined in Uri. i.e. content:/media.../id
Shash

Need suggestion about a mixed "Uri / int id" images ambient

I have the following problem:
suppose that until now, I am using R.drawable.img to set the image in some imageviews
with
imgView.setImage(aProduct.getImgId());
the simplified product class look like this:
class Product{
int imgId;
....
public void setImgId(int id){
this.imgId=id;
}
public int getImgId(){
return this.imgId
}
...
}
my application is now "evolved" because the user can add customized products
taking the img from the camera and getting the Uri of the picture.
and to set the image on the ImageView imgView.setImgURI(Uri)
Now my question is:
what would be the best approach to have a mixed int/Uri image resources ambient?
can I obtain the Uri of a "R.drawable.img"?
I'm not sure if my question is clear, I mean:
I have to check, before to set the imageview, if my product has an Uri or an int Id,
and then make an "if" to call the appropriate method, or there is a simpler solution?
Thank you for reading, and sorry for my english.
Regards.

Your problem is that there are basically 3 types of image resources:
R.id... resources: internal resources, such as icons you put into the res folder
content URI's: local files or content provider resources such as content:// or file:///sdcard/...
remote file URL's: images on the web, such as http://...
You are looking for a way to pass around one identifier that can deal with all three. My solution was to pass around a string: either the toString() of the URI's, or just the string respresentation of the R.id integer.
I'm using the following code, for example, to deal with this and make the code work with it:
public static FastBitmapDrawable returnAndCacheCover(String cover, ImageRepresentedProductArtworkCreator artworkCreator) {
Bitmap bitmap = null;
Uri coverUri = null;
boolean mightBeUri = false;
//Might be a resId. Needs to be cached. //TODO: problem: resId of default cover may not survive across versions of the app.
try {
bitmap = BitmapFactory.decodeResource(Collectionista.getInstance().getResources(), Integer.parseInt(cover));
} catch (NumberFormatException e) {
//Not a resId after all.
mightBeUri=true;
}
if(bitmap==null || mightBeUri){
//Is not a resId. Might be a contentUri.
try {
coverUri = Uri.parse(cover);
} catch (NullPointerException ne) {
//Is null
return null;
}
}
if(coverUri!=null){
if(coverUri.getScheme().equals("content")){
//A contentUri. Needs to be cached.
try {
bitmap = MediaStore.Images.Media.getBitmap(Collectionista.getInstance().getContentResolver(), coverUri);
} catch (FileNotFoundException e) {
return null;
} catch (IOException e) {
return null;
}
}else{
//Might be a web uri. Needs to be cached.
bitmap = loadCoverFromWeb(cover);
}
}
return new FastBitmapDrawable(bitmap);
}
You might be interested to take over the logic part. Ofcourse cover is the string in question here.
Forget android.resource:// as a replacement for the R.id... integer. Claims are going round it does not work: http://groups.google.com/group/android-developers/browse_thread/thread/a672d71dd7df4b2d
To find out how to implement loadCoverFromWeb, have a look around in other questions or ping me. This web stuff is kind of a field of it's own.
(Based on GPLv3 code out of my app Collectionista: https://code.launchpad.net/~pjv/collectionista/trunk)