Cannot open PDF file in external app

Question

I would like to open a PDF file when the user clicks on a button. Currently, i am using this code to achieve this:

Uri path = Uri.fromFile(new File("file:///android_asset/regola11_1.pdf"));
            Intent pdfIntent = new Intent(Intent.ACTION_VIEW);
            pdfIntent.setDataAndType(path, "application/pdf");
            pdfIntent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
            startActivity(pdfIntent);

but it doesn't work.

When i select to use Adobe Acrobat, i get a message, displayed as a Toast, that says

"This file could not be accessed Check the location or the network and try again."

When i try with Drive PDF Viewer, i get

"Cannot display PDF ( regola11_1.pdf cannot be opened)"

The PDF file is stored in

app > build > intermediates > assets

Where is the problem?

EDIT

Now i'm using the following code:

File file = new File("\"file:///android_asset/regola11_1.pdf");
            Uri path = Uri.fromFile(file);
            Intent intent = new Intent(Intent.ACTION_VIEW);
            intent.setDataAndType(path, "application/pdf");
            intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);

            try {
                context.startActivity(intent);
            }
            catch (ActivityNotFoundException e) {
                Toast.makeText(context, "No application available to view PDF", Toast.LENGTH_LONG).show();
            }

But when i try to open the PDF by clicking on the button, the app crashes.

This is the log i get:

05-31 10:05:25.132  24474-24474/? E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.andrey.andreyvedis.iamaref, PID: 24474
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.content.Context.startActivity(android.content.Intent)' on a null object reference
        at com.andrey.andreyvedis.iamaref.FragmentR11.onClick(FragmentR11.java:147)
        at android.view.View.performClick(View.java:4781)
        at android.view.View$PerformClick.run(View.java:19873)
        at android.os.Handler.handleCallback(Handler.java:739)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:135)
        at android.app.ActivityThread.main(ActivityThread.java:5293)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:904)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:699)

This is my class:

public class FragmentR11 extends Fragment implements  View.OnClickListener{
// TODO: Rename parameter arguments, choose names that match
// the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
private static final String ARG_PARAM1 = "param1";
private static final String ARG_PARAM2 = "param2";
Context context;



// TODO: Rename and change types of parameters
private String mParam1;
private String mParam2;


/**
 * Use this factory method to create a new instance of
 * this fragment using the provided parameters.
 *
 * @param param1 Parameter 1.
 * @param param2 Parameter 2.
 * @return A new instance of fragment FragmentR11.
 */
// TODO: Rename and change types and number of parameters
public static FragmentR11 newInstance(String param1, String param2) {
    FragmentR11 fragment = new FragmentR11();
    Bundle args = new Bundle();
    args.putString(ARG_PARAM1, param1);
    args.putString(ARG_PARAM2, param2);
    fragment.setArguments(args);
    return fragment;
}

public FragmentR11() {
    // Required empty public constructor
}

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    if (getArguments() != null) {
        mParam1 = getArguments().getString(ARG_PARAM1);
        mParam2 = getArguments().getString(ARG_PARAM2);
    }



}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    return inflater.inflate(R.layout.fragment_r11, container, false);


}

@Override
public void onViewCreated(View view, Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);

    getActivity().findViewById(R.id.bD1).setOnClickListener(this);
    getActivity().findViewById(R.id.bD2).setOnClickListener(this);
    getActivity().findViewById(R.id.bD3).setOnClickListener(this);
    getActivity().findViewById(R.id.bD4).setOnClickListener(this);
    getActivity().findViewById(R.id.bD5).setOnClickListener(this);
    getActivity().findViewById(R.id.bD6).setOnClickListener(this);
    getActivity().findViewById(R.id.bD7).setOnClickListener(this);
    getActivity().findViewById(R.id.bD8).setOnClickListener(this);
    getActivity().findViewById(R.id.bD9).setOnClickListener(this);
    getActivity().findViewById(R.id.bD10).setOnClickListener(this);
    getActivity().findViewById(R.id.bD11).setOnClickListener(this);
    getActivity().findViewById(R.id.bD12).setOnClickListener(this);
    getActivity().findViewById(R.id.bD13).setOnClickListener(this);
    getActivity().findViewById(R.id.bD14).setOnClickListener(this);
    getActivity().findViewById(R.id.bD15).setOnClickListener(this);
    getActivity().findViewById(R.id.bD16).setOnClickListener(this);
    getActivity().findViewById(R.id.bD17).setOnClickListener(this);


}

/**private void openPDF(final String pathToPDF) {
    File file = new File(pathToPDF);
    Uri path = Uri.fromFile(file);
    Intent intent = new Intent(Intent.ACTION_VIEW);
    intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
    intent.setDataAndType(path, "application/pdf");
    try {
        startActivity(intent);
    } catch (ActivityNotFoundException e) {
        Toast.makeText(getActivity(), "Devi installare un'app per aprire PDF, come Adobe Acrobat Reader ", Toast.LENGTH_SHORT).show();
    }
}*/


@Override
public void onClick(View v) {



    switch(v.getId()){

        case R.id.bD1: {

            /**Uri path = Uri.fromFile(new File("regola11_1.pdf"));
            Intent pdfIntent = new Intent(Intent.ACTION_VIEW);
            pdfIntent.setDataAndType(path, "application/pdf");
            pdfIntent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
            startActivity(pdfIntent);
            Toast.makeText(getActivity(), "Hai cliccato Regola 1 in Reg11 ", Toast.LENGTH_SHORT).show();*/

            File file = new File("\"file:///android_asset/regola11_1.pdf");
            Uri path = Uri.fromFile(file);
            Intent intent = new Intent(Intent.ACTION_VIEW);
            intent.setDataAndType(path, "application/pdf");
            intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);

            try {
                context.startActivity(intent);
            }
            catch (ActivityNotFoundException e) {
                Toast.makeText(context, "No application available to view PDF", Toast.LENGTH_LONG).show();
            }
            break;
        }

        case R.id.bD2:

        {
            Toast.makeText(getActivity(), "Hai cliccato Regola 2 in Reg11 ", Toast.LENGTH_SHORT).show();

            break;
        }


        case R.id.bD3:

        {
            Toast.makeText(getActivity(), "Hai cliccato Regola 3 in Reg11 ", Toast.LENGTH_SHORT).show();

            break;
        }

        case R.id.bD4:

        {
            Toast.makeText(getActivity(), "Hai cliccato Regola 4 in Reg11 ", Toast.LENGTH_SHORT).show();

            break;
        }

        case R.id.bD5:

        {
            Toast.makeText(getActivity(), "Hai cliccato Regola 5 in Reg11 ", Toast.LENGTH_SHORT).show();

            break;
        }

        case R.id.bD6:

        {
            Toast.makeText(getActivity(), "Hai cliccato Regola 6 in Reg11 ", Toast.LENGTH_SHORT).show();

            break;
        }

        case R.id.bD7:

        {
            Toast.makeText(getActivity(), "Hai cliccato Regola 7 in Reg11 ", Toast.LENGTH_SHORT).show();

            break;
        }

        case R.id.bD8:

        {
            Toast.makeText(getActivity(), "Hai cliccato Regola 8 in Reg11 ", Toast.LENGTH_SHORT).show();

            break;
        }

        case R.id.bD9:

        {
            Toast.makeText(getActivity(), "Hai cliccato Regola 9 in Reg11 ", Toast.LENGTH_SHORT).show();

            break;
        }

        case R.id.bD10:

        {
            Toast.makeText(getActivity(), "Hai cliccato Regola 10 in Reg11 ", Toast.LENGTH_SHORT).show();

            break;
        }

        case R.id.bD11:

        {
            Toast.makeText(getActivity(), "Hai cliccato Regola 11 in Reg11 ", Toast.LENGTH_SHORT).show();

            break;
        }

        case R.id.bD12:

        {
            Toast.makeText(getActivity(), "Hai cliccato Regola 12 in Reg11 ", Toast.LENGTH_SHORT).show();

            break;
        }

        case R.id.bD13:

        {
            Toast.makeText(getActivity(), "Hai cliccato Regola 13 in Reg11 ", Toast.LENGTH_SHORT).show();

            break;
        }

        case R.id.bD14:

        {
            Toast.makeText(getActivity(), "Hai cliccato Regola 14 in Reg11 ", Toast.LENGTH_SHORT).show();

            break;
        }

        case R.id.bD15:

        {
            Toast.makeText(getActivity(), "Hai cliccato Regola 15 in Reg11 ", Toast.LENGTH_SHORT).show();

            break;
        }

        case R.id.bD16:

        {
            Toast.makeText(getActivity(), "Hai cliccato Regola 16 in Reg11 ", Toast.LENGTH_SHORT).show();

            break;
        }

        case R.id.bD17:

        {
            Toast.makeText(getActivity(), "Hai cliccato Regola 17 in Reg11 ", Toast.LENGTH_SHORT).show();

            break;
        }


    }

}

}

Can someone help me?

EDIT 2

I have found the solution, check my answer below for the code.

Thank you all for your answers.

Answer 1

For newer API you can open PDF in WebView, see Load PDF file in webview. I tested, on API 21 device it offered several applications to open, in API 27 it opened inside WebView.

For usual opening in external reader copy this code. I used: intent.resolveActivity != null but launching the intent throws an ActivityNotFound exception, https://stackoverflow.com/a/57141679/2914140. You should define FileProvider first.

// Try to open PDF and return false if it is not possible.
fun openPdf(file: File, context: Context): Boolean {
    val uri = getUriFromFile(file, context)
    if (uri == null) {
        return false
    } else {
        val intent = Intent(Intent.ACTION_VIEW).apply {
            setDataAndType(uri, "application/pdf")
            flags = Intent.FLAG_ACTIVITY_CLEAR_TOP
            addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION)
        }
        // Validate that the device can open your File.
        val activityInfo = intent.resolveActivityInfo(context.packageManager, intent.flags)
        return if (activityInfo?.exported == true) {
            context.startActivity(Intent.createChooser(intent, "Open PDF")))
            true
        } else {
            false
        }
    }
}

// Get URI from file.
fun getUriFromFile(file: File, context: Context): Uri? =
    if (Build.VERSION.SDK_INT < Build.VERSION_CODES.LOLLIPOP) {
        Uri.fromFile(file)
    } else {
        try {
            FileProvider.getUriForFile(context, context.packageName + ".provider", file)
        } catch (e: Exception) {
            if (e.message?.contains("ProviderInfo.loadXmlMetaData") == true) {
                throw Error("FileProvider doesn't exist or has no permissions")
            } else {
                throw e
            }
        }
    }

In API 29 emulator (without PDF applications) I found that it opened PDF in built-in library.