android.os.FileUriExposedException being caused in Oreo (only!)

Question

From the Google Play Console, I can see that this exception is only happening on devices with Android 8.0+.

android.os.FileUriExposedException: 
at android.os.StrictMode.onFileUriExposed (StrictMode.java:1975)
at android.net.Uri.checkFileUriExposed (Uri.java:2355)
at android.content.Intent.prepareToLeaveProcess (Intent.java:9975)
at android.content.Intent.prepareToLeaveProcess (Intent.java:9950)
at android.content.Intent.prepareToLeaveProcess (Intent.java:9929)
at android.app.Instrumentation.execStartActivity (Instrumentation.java:1622)
at android.app.Activity.startActivityForResult (Activity.java:4748)
at android.support.v4.app.BaseFragmentActivityJB.startActivityForResult (BaseFragmentActivityJB.java:10)
at android.support.v4.app.FragmentActivity.startActivityForResult (FragmentActivity.java)
at android.support.v4.app.ActivityCompatJB.finishAffinity (ActivityCompatJB.java)
or                                         .startActivityForResult (ActivityCompatJB.java)
at android.support.v4.app.ActivityCompat.a (ActivityCompat.java:6)
at android.support.v4.app.FragmentActivity.a (FragmentActivity.java:8)
at android.support.v4.app.FragmentActivity$HostCallbacks.a (FragmentActivity.java:2)
at android.support.v4.app.Fragment.a (Fragment.java:38)
at android.support.v4.app.Fragment.a (Fragment.java:1)
at de.test.testapp.FileManagerFragment.onClick (FileManagerFragment.java:113)
at android.view.View.performClick (View.java:6291)
at android.view.View$PerformClick.run (View.java:24931)
at android.os.Handler.handleCallback (Handler.java:808)
at android.os.Handler.dispatchMessage (Handler.java:101)
at android.os.Looper.loop (Looper.java:166)
at android.app.ActivityThread.main (ActivityThread.java:7390)
at java.lang.reflect.Method.invoke (Method.java)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run (Zygote.java:245)
at com.android.internal.os.ZygoteInit.main (ZygoteInit.java:926)

the code:

Intent intent = new Intent(Intent.ACTION_VIEW);
ArrayList<Uri> uri = new ArrayList<Uri>();
for (int i=0; i<checkedItems.size(); i++) {
    if (checkedItems.valueAt(i)) {
        intent.setDataAndType(Uri.fromFile(new File(projectDir, filename), "text/plain");
    }
}
intent.putParcelableArrayListExtra(Intent.EXTRA_STREAM, uri);
startActivity(Intent.createChooser(intent, "Open RINEX File"));

Manifest:

<?xml version="1.0" encoding="utf-8"?>

<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

<!-- To access Google+ APIs: -->
<uses-permission android:name="android.permission.INTERNET" />

<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:supportsRtl="true"
    android:theme="@style/AppTheme">
    <activity
        android:name=".MainActivity"
        android:screenOrientation="portrait">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>

    <provider
        android:name="android.support.v4.content.FileProvider"
        android:authorities="de.test.testapp"
        android:exported="false"
        android:grantUriPermissions="true">
        <meta-data
            android:name="android.support.FILE_PROVIDER_PATHS"
            android:resource="@xml/file_providers_paths" />
    </provider>
</application>

file_providers_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>

Why does this work on Android 7 but not on Android 8 anymore? What behaviour changes have happened? I am calling this within a fragment.

Answer 1

Try adding this inside onCreate.

StrictMode.VmPolicy.Builder builder = new StrictMode.VmPolicy.Builder();
StrictMode.setVmPolicy(builder.build());
builder.detectFileUriExposure();