Custom Dialog öffnet nicht

[CSharper]

Wieso bekomme ich in immer eine NullPointerReference Exception?

Meine Clickmethode, die ein Custom Dialog aufrufen soll:

/* Register btn_newRoute in onCreate() */
		ImageView open_add_new_car_diolog_btn = (ImageView) findViewById(R.id.add_new_car_btn);
		open_add_new_car_diolog_btn.setOnClickListener(new OnClickListener()
		{
			@Override
			public void onClick( View v )
			{
				/*
				 * custom dialog Add new car dialog
				 */
				final Dialog add_new_car_dialog = new Dialog(CarsActivity.this);
				add_new_car_dialog.setContentView(R.layout.add_new_car_layout);
				add_new_car_dialog.setTitle(getResources().getString(R.string.add_new_car_popup_Title));
				add_new_car_dialog.show();

				// Set custom dialog items
				TextView make_lbl = (TextView) add_new_car_dialog.findViewById(R.id.Make_lbl);
				make_lbl.setText(R.string.make_lbl);

				TextView mileage_lbl = (TextView) add_new_car_dialog.findViewById(R.id.Milage_lbl);
				mileage_lbl.setText(R.string.mileage_lbl);

				TextView model_lbl = (TextView) add_new_car_dialog.findViewById(R.id.Model_lbl);
				model_lbl.setText(R.string.model_lbl);

				EditText makeEditText = (EditText) add_new_car_dialog.findViewById(R.id.edit_make_txt);
				makeEditText.setText(R.string.add_new_car_make_editText);

				EditText modelEditText = (EditText) add_new_car_dialog.findViewById(R.id.edit_model_txt);
				modelEditText.setText(R.string.add_new_car_model_editText);

				EditText mileageEditText = (EditText) add_new_car_dialog.findViewById(R.id.edit_mileage_txt);
				mileageEditText.setText(R.string.add_new_car_mileage_editText);

				/* Register btn_newRoute in onCreate() */
				ImageView add_new_car_ok_btn = (ImageView) findViewById(R.id.add_new_car_ok_btn);
				add_new_car_ok_btn.setOnClickListener(new OnClickListener()
				{
					public void onClick( View v )
					{
						// ToDo: Code after Click
						Toast.makeText(CarsActivity.this, "add_new_car_ok_btn is clicked!", Toast.LENGTH_SHORT).show();
					}
				});

				/* Register btn_newRoute in onCreate() */
				ImageView add_new_car_cancel_btn = (ImageView) findViewById(R.id.add_new_car_cancel_btn);
				add_new_car_cancel_btn.setOnClickListener(new OnClickListener()
				{
					public void onClick( View v )
					{
						// ToDo: Code after Click
						Toast.makeText(CarsActivity.this, "add_new_car_cancel_btn is clicked!", Toast.LENGTH_SHORT).show();
					}
				});

			}
		});

Und hier das Layout für den custom dialog!

<?xml version="1.0" encoding="utf-8"?>
<TableLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content" >

    <TableRow
        android:id="@+id/add_new_car_layout_row1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_weight="1" >

        <TextView
            android:id="@+id/Make_lbl"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_gravity="right"
            android:layout_margin="5dp"
            android:gravity="center"
            android:text="@string/make_lbl" />
        
        <EditText
            android:id="@+id/edit_make_txt"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_margin="5dp"
            android:gravity="left"
            android:text="make" />

    </TableRow>

    <TableRow
        android:id="@+id/add_new_car_layout_row2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" 
        android:layout_weight="1" >

        <TextView
            android:id="@+id/Model_lbl"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_gravity="right"
            android:layout_margin="5dp"
            android:gravity="center"
            android:text="@string/model_lbl" />
        
        <EditText
            android:id="@+id/edit_model_txt"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_margin="5dp"
            android:gravity="left"
            android:text="model" />

    </TableRow>

    <TableRow
        android:id="@+id/add_new_car_layout_row3"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" 
        android:layout_weight="1" >

        <TextView
            android:id="@+id/Milage_lbl"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="right"
            android:layout_margin="5dp"
            android:gravity="center"
            android:text="@string/mileage_lbl" />

        <EditText
            android:id="@+id/edit_mileage_txt"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_margin="5dp"
            android:inputType="number"
            android:text="mileage" />

    </TableRow>
    
    <TableRow
        android:id="@+id/add_new_car_layout_row4"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_weight="1" >

        <ImageView
            android:id="@+id/add_new_car_ok_btn"
            android:layout_width="wrap_content"
            android:layout_height="50dp"
            android:layout_margin="10dp"
            android:layout_weight="1"
            android:src="@drawable/custom_dialog_ok" />

        <ImageView
            android:id="@+id/add_new_car_cancel_btn"
            android:layout_width="wrap_content"
            android:layout_height="50dp"
            android:layout_margin="10dp"
            android:layout_weight="1"
            android:src="@drawable/custom_dialog_cancel" /> 
    </TableRow>

</TableLayout>