Xamarin C# “we don't have access to open this file” When I Trying To Open A PDF

Question

MainActivity.cs:

Java.IO.File file = new Java.IO.File(filePath);
        Android.Net.Uri uri = FileProvider.GetUriForFile(this, "com.companyname.quickexam_final.FileProvider", file);
        Intent intent = new Intent(Intent.ActionView);
        intent.SetDataAndType(uri, "application/pdf");
        intent.SetFlags(ActivityFlags.ClearWhenTaskReset | ActivityFlags.NewTask);


        this.StartActivity(intent);

Manifest.xml

<?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.quickexam_final" android:installLocation="auto">
    <uses-sdk android:minSdkVersion="20" android:targetSdkVersion="28" />
    <application android:allowBackup="true" android:label="@string/app_name" android:roundIcon="@mipmap/ic_launcher_round" android:supportsRtl="true" android:theme="@style/AppTheme" android:icon="@mipmap/ic_launcher">
        <provider android:name="android.support.v4.content.FileProvider" android:authorities="com.companyname.quickexam_final.FileProvider" android:exported="false" android:grantUriPermissions="true">
            <meta-data android:name="android.support.FILE_PROVIDER_PATHS" android:resource="@xml/provider_paths" />
        </provider>
    </application>
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.INTERNET" />
</manifest>

provider_paths.xml

<?xml version="1.0" encoding="utf-8"?>
<paths xmlns:android="http://schemas.android.com/apk/res/android">
  <external-path name="external_files" path="."/>
</paths>

Then, when I start my app I see a Toast

"We don't have access to open this file."

How can I solve this problem?

Answer 1

I would guess that this is because for persmissions that are regarded as dangerous, you need to explicitly request them. It is not enough just to have them in the manifest. To solve it you should use ActivityCompat.RequestPermissions to explicitly request access to these.

If you check the spec here it lists, for example, "READ_EXTERNAL_STORAGE" as a dangerous permission requiring an explicit prompt. https://developer.android.com/reference/android/Manifest.permission#READ_EXTERNAL_STORAGE

You can see here more about this issue: https://developer.android.com/guide/topics/permissions/overview#dangerous-permission-prompt