Android 6: cannot share files anymore?

I solved it by implementing a FileProvider, as suggested by @CommonsWare

You first need to configure a FileProvider:

• first, add the <provider> to your file manifest XML

  <provider
      android:name="android.support.v4.content.FileProvider"
      android:authorities="com.myfileprovider"
      android:exported="false"
      android:grantUriPermissions="true">
      <meta-data
          android:name="android.support.FILE_PROVIDER_PATHS"
          android:resource="@xml/file_provider_paths" />
  </provider>
  

• second, define your file paths in a separate XML file, I called it “file_provider_paths.xml“

  <paths xmlns:android="http://schemas.android.com/apk/res/android">
      <external-path name="share" path="https://stackoverflow.com/" />
  </paths>
  

you can find the complete explanation in this documentation page

after you have set up your file provider in XML, this is the code to share the image file:

Intent shareIntent = new Intent(Intent.ACTION_SEND);
shareIntent.setType("image/*");
Uri fileUri = FileProvider.getUriForFile(mContext, "com.myfileprovider", new File(mFilename));
shareIntent.addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION);
shareIntent.putExtra(Intent.EXTRA_STREAM, fileUri);
mContext.startActivity(Intent.createChooser(shareIntent, mChooserTitle));