Show a dialogue on android

I have a problem: I want to show a dialogue that I made from a layout that has a text and a button but I do not understand because it tells me that the application stopped.

Code:

public class MainActivity extends AppCompatActivity {

    Button b1;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        b1 = (Button) findViewById(R.id.b1);
    }

    public void b1(View view) {

        AlertDialog.Builder alertDialogBuilder = new AlertDialog.Builder(MainActivity.this);

        View child = getLayoutInflater().inflate(R.layout.dialogo6, null);
        alertDialogBuilder.setView(child);

        final AlertDialog alertDialog = alertDialogBuilder.create();
        alertDialog.getWindow().setBackgroundDrawableResource(android.R.color.transparent);

        Button dismissButton = (Button) alertDialog.findViewById(R.id.boton);
        dismissButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                alertDialog.dismiss();
            }
        });

        alertDialog.show();
    }
}

The dialogue that I want to show:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent">

<TextView
    android:text="Alto Titulo Ameo"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:id="@+id/titulo"
    android:textAlignment="center"
    android:textSize="30sp" />

<ScrollView
    android:layout_width="match_parent"
    android:layout_height="340dp">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical" >

        <ImageView
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            app:srcCompat="@mipmap/ic_launcher"
            android:id="@+id/imagen" />

        <TextView
            android:text="Descripcion del dialogo"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:id="@+id/desc"
            android:textSize="20sp" />

    </LinearLayout>
</ScrollView>

<Button
    android:text="Button"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:id="@+id/boton"/>
</LinearLayout>