Android - Elegir imagen y compartirla en Gmail.

import android.app.Activity;

import android.content.Intent;

import android.database.Cursor;

import android.net.Uri;

import android.os.Bundle;

import android.provider.MediaStore;

import android.util.Log;

import android.view.View;

import android.view.View.OnClickListener;

import android.widget.Button;

import android.widget.EditText;

import android.widget.Toast;

/**

 *

 * @author manish

 *

 */

public class MainActivity extends Activity implements OnClickListener {

    EditText editTextEmail, editTextSubject, editTextMessage;

    Button btnSend, btnAttachment;

    String email, subject, message, attachmentFile;

    Uri URI = null;

    private static final int PICK_FROM_GALLERY = 101;

    int columnIndex;

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        editTextEmail = (EditText) findViewById(R.id.editTextTo);

        editTextSubject = (EditText) findViewById(R.id.editTextSubject);

        editTextMessage = (EditText) findViewById(R.id.editTextMessage);

        btnAttachment = (Button) findViewById(R.id.buttonAttachment);

        btnSend = (Button) findViewById(R.id.buttonSend);

        btnSend.setOnClickListener(this);

        btnAttachment.setOnClickListener(this);

    }

    protected void onActivityResult(int requestCode, int resultCode, Intent data) {

        if (requestCode == PICK_FROM_GALLERY && resultCode == RESULT_OK) {

            /**

             * Get Path

             */

            Uri selectedImage = data.getData();

            String[] filePathColumn = { MediaStore.Images.Media.DATA };

            Cursor cursor = getContentResolver().query(selectedImage,filePathColumn, null, null, null);

            cursor.moveToFirst();

            columnIndex = cursor.getColumnIndex(filePathColumn[0]);

            attachmentFile = cursor.getString(columnIndex);

            Log.e("Attachment Path:", attachmentFile);

            URI = Uri.parse("file://" + attachmentFile);

            cursor.close();

        }

    }

    @Override

    public void onClick(View v) {

        if (v == btnAttachment) {

            openGallery();

        }

        if (v == btnSend) {

            try {

                email = editTextEmail.getText().toString();

                subject = editTextSubject.getText().toString();

                message = editTextMessage.getText().toString();

                final Intent emailIntent = new Intent(

                        android.content.Intent.ACTION_SEND);

                emailIntent.setType("plain/text");

                emailIntent.putExtra(android.content.Intent.EXTRA_EMAIL,

                        new String[] { email });

                emailIntent.putExtra(android.content.Intent.EXTRA_SUBJECT,

                        subject);

                if (URI != null) {

                    emailIntent.putExtra(Intent.EXTRA_STREAM, URI);

                }

                emailIntent

                        .putExtra(android.content.Intent.EXTRA_TEXT, message);

                this.startActivity(Intent.createChooser(emailIntent,

                        "Sending email..."));

            } catch (Throwable t) {

                Toast.makeText(this,

                        "Request failed try again: " + t.toString(),

                        Toast.LENGTH_LONG).show();

            }

        }

    }

    public void openGallery() {

        Intent intent = new Intent();

        intent.setType("image/*");

        intent.setAction(Intent.ACTION_GET_CONTENT);

        intent.putExtra("return-data", true);

        startActivityForResult(

                Intent.createChooser(intent, "Complete action using"),

                PICK_FROM_GALLERY);

    }

}

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

<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"

    xmlns:app="http://schemas.android.com/apk/res-auto"

    xmlns:tools="http://schemas.android.com/tools"

    android:layout_width="match_parent"

    android:layout_height="match_parent"

    tools:context=".MainActivity">

    <RelativeLayout

        android:layout_width="match_parent"

        android:layout_height="match_parent"

        android:layout_margin="5dp"

        android:padding="5dp" >

        <EditText

            android:id="@+id/editTextTo"

            android:layout_width="wrap_content"

            android:layout_height="wrap_content"

            android:layout_alignParentLeft="true"

            android:layout_alignParentTop="true"

            android:layout_margin="5dp"

            android:hint="Email Address!"

            android:inputType="textEmailAddress"

            android:singleLine="true" />

        <EditText

            android:id="@+id/editTextSubject"

            android:layout_width="match_parent"

            android:layout_height="wrap_content"

            android:layout_below="@id/editTextTo"

            android:layout_margin="5dp"

            android:hint="Subject"

            android:singleLine="true" />

        <EditText

            android:id="@+id/editTextMessage"

            android:layout_width="match_parent"

            android:layout_height="200dp"

            android:layout_below="@id/editTextSubject"

            android:layout_margin="5dp"

            android:gravity="top|left"

            android:hint="type message here!"

            android:inputType="textMultiLine" />

        <Button

            android:id="@+id/buttonSend"

            android:layout_width="80dp"

            android:layout_height="50dp"

            android:layout_below="@id/editTextMessage"

            android:layout_margin="5dp"

            android:text="Send" />

        <Button

            android:id="@+id/buttonAttachment"

            android:layout_width="wrap_content"

            android:layout_height="50dp"

            android:layout_alignParentRight="true"

            android:layout_alignParentTop="true"

            android:text="attachment" />

    </RelativeLayout>

</android.support.constraint.ConstraintLayout>

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

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

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

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

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