Develop Reference

Xamarin android display image from external Storage

I'm currently trying to displa an image from the storage, but I have no success.
What I'm dooing.
public Stream ReadImage(string path)
{
//var uri = Android.Net.Uri.Parse(path);
//var stream = MainActivity._activity.ContentResolver.OpenInputStream(uri);
//return stream;
var memoryStream = new MemoryStream();
using (var source = System.IO.File.OpenRead(path))
{
source.CopyTo(memoryStream);
}
return memoryStream;
}
string path = "/storage/emulated/0/DCIM/Camera/IMG_20190521_094202.jpg"
var imageSource = ImageSource.FromStream(
delegate {
return DependencyService.Get<IMediaHelper>().ReadImage(path);
});
But in the using line the programm doese not proceed, it does not reach the following lines and it does not load the file from the storage, the way with the contetn resolver does end teh same way, in the contentresolver line.
I have the Read/write external storage permission.
I am using android x, with Xamarin 5.0.0.2012. Under android 10 & and 11, on multiple different xiaomi devices.
This might be a bug, because I think, I had it running in an earlier project.
Some insight woult be appreciated, I'm biting my teath out on this nut.

To give users more control over their files and to limit file clutter, apps that target Android 10 (API level 29) and higher are given scoped access into external storage, or scoped storage, by default. Such apps have access only to the app-specific directory on external storage, as well as specific types of media that the app has created.You could read it here.
For android 10,you could request the requestLegacyExternalStorage attribute in your Application tag in the AndroidManifest.
<application android:label="NewForms.Android" android:resizeableActivity="true" android:requestLegacyExternalStorage="true" android:theme="#style/MainTheme">
For android 11,you need add <uses-permission android:name="android.permission.MANAGE_EXTERNAL_STORAGE" /> in your AndroidManifest.And determine in the Activity whether the permission is enabled.
And you can't forget to dynamically request WRITE_EXTERNAL_STORAGE permissions (this was added after Android 6.0,named Runtime Permissions).
The final code is as follows：
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android" android:versionCode="1" android:versionName="1.0" package="com.companyname.newforms" android:installLocation="preferExternal">
<uses-sdk android:minSdkVersion="18" android:targetSdkVersion="30" />
<application android:label="NewForms.Android" android:requestLegacyExternalStorage="true" android:theme="#style/MainTheme"></application>
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.MANAGE_EXTERNAL_STORAGE" />
</manifest>
and you could request the runtime permission like this in your MainActivity:
RequestPermissions(new string[] { Manifest.Permission.WriteExternalStorage}, 0);
if (Build.VERSION.SdkInt > BuildVersionCodes.Q)
{
if (!Environment.IsExternalStorageManager)
{
StartActivityForResult(new Intent( Android.Provider.Settings.ActionManageAllFilesAccessPermission), 101);
}
}

android APN How to read and write it?

i work on a app (> 4.4) and my boss would like to save the configuration of the APN into the SQLite (our database).
As this, if the APN is lost for a reason we can retrieve easily these information and configure it ..
well, i've try some code but actually NOTHING work ...
I have this error message
Java.Lang.SecurityException: No permission to write APN settings: Neither user 10081 nor current process has android.permission.WRITE_APN_SETTINGS.
Of course, i have added to the manifest the correct RIGTH as this
<uses-permission android:name="android.permission.READ_APN_SETTINGS"></uses-permission>
<uses-permission android:name="android.permission.WRITE_APN_SETTINGS"></uses-permission>
<uses-feature android:name="android.hardware.telephony" android:required="false" />
And here is it my code, it's with xamarin android but if you have some code with android , no matter i can find the translatation ..
Android.Net.Uri APN_TABLE_URI = Android.Net.Uri.Parse("content://telephony/carriers");
//path to preffered APNs
Android.Net.Uri PREFERRED_APN_URI = Android.Net.Uri.Parse("content://telephony/carriers/preferapn");
//
Android.Database.ICursor cursor = ctx.ContentResolver.Query(PREFERRED_APN_URI, null, null, null, null);
Thanks guys for all your time you spend here for to share your knowledge

try to add these two permissions:
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

Can't Read Files in Sdcard in emulator

I have some problems in my App.
I just wanna read file in sdcard, so I put the file in /storage/sdcard/abcd (the folder I made by adb) in emulator.
File name is "1.14P", and I verify it is in that path. Its permission is 770.
But my problem is, I can't access sdcard by Application.
sampleFile = new File (Environment.getExternalStorageDirectory(), "abcd/1.14P");
sampleFile.exists() //return false
sampleFile2 = new File (Environment.getExternalStorageDirectory(), "tttt");
sampleFile2.mkdir() //return false
Sdcard is mounted well, I thought.
String state = Environment.getExternalStorageState(); //return "mounted"
I give the permission but I can't access to sdcard. Here is my manifest.xml. (part)
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.hu.test004" >
<uses-permission android:name="ANDROID.PERMISSION.WRITE_EXTERNAL_STORAGE"/>
<uses-permission android:name="ANDROID.PERMISSION.READ_EXTERNAL_STORAGE"/>
<application
android:allowBackup="true"
android:icon="#mipmap/ic_launcher"
android:label="#string/app_name"
android:theme="#style/AppTheme" >
...(Activities)
I can't understand why it happens. Please give me some favor. Thanks.

SOLVED::I've got it!
The problem is, I declared permissions in capital letter, so App doesn't grant permissions.
I change
<uses-permission android:name="ANDROID.PERMISSION.WRITE_EXTERNAL_STORAGE"/>
<uses-permission android:name="ANDROID.PERMISSION.READ_EXTERNAL_STORAGE"/>
to
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
and permission granted.
Thank you for your favor all.

I think the "," is part of the problem. The other is the "exists()" is for directories, not files.
See here:
new File(path) always actually creates a file on android?
contrary to the docs:
http://developer.android.com/reference/java/io/File.html
you may want to use isFile() instead.

Could you try adding "/" in front of your names??
e.g. "/abcd/1.14P"

How to display html page kept on sdcard on webview

I am not able to display html page kept in sdcard on webview. I have tried using this two methods:
webPage.loadUrl("file://"+ Environment.getExternalStorageDirectory()+"/page1.html");
and
webPage.loadUrl("content://com.android.htmlfileprovider"+
Environment.getExternalStorageDirectory()+"/page1.html");
Please Guide.

Try This.
webPage.loadUrl("file://"+Environment.getExternalStorageDirectory()+"/page1.html");
You forgot to add slash.
Add Internet Permission and Read External Permission.
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>

Why Images.Media.insertImage doesn't require WRITE_EXTERNAL_STORAGE permission

I realize even I do not have
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
in my `AndroidManifest.xml
String path = Images.Media.insertImage(((Activity)MainView.this.getContext()).getContentResolver(), screenCaptureBitmap, "Title", "Description");
still able to write image file to location /mnt/sdcard/DCIM/Camera. May I know why is it so?

maybe in depend on the content provider MediaStore, you through it to insert, it's a RPC invoke. and the MediaStore provider in source code: packages/providers/MediaProvider, in it's manifest define the permission
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />,
may be it's the reason.