Creating option to allow user to select the page my plugin content will display on

Question

I have an options page for my plugin, but cannot seem to figure out how to create an option to allow admins to select a page that will display my plugins content.

Does anyone have an example of how this is done?

EDIT: I created a plugin and have a widget to search the content of my plugin. However I need the widget to post to the page that my plugins content is being displayed on. Since the widget is on the sidebar it could be submitted from any page, I need to be able to detect which page the plugin content is being displayed on and se the to that page. 1. detect the shortcode on a given page, and use that. OR 2. Create an option from a settings page to allow the admin to select which page the plugin content will be displayed on and get rid of the shortcode. I hope that clarifies.

I have a settings page for my plugin, I just do not understand how to get a list of the available pages and save/update the option in the wp_options table.

Answer 1

Here's a quick options page that will give you a dropdown select for choosing a page, using the get_pages function. The Settings API takes care of saving the options for you. You can then use get_option to load the options array in your template, and get_post to load the post data associated with the ID saved in your option.

add_action( 'admin_init', 'russ_options_init' );
add_action( 'admin_menu', 'russ_options_page' );

function russ_options_init(){
    register_setting(
        'russ_options_group',
        'russ_options',
        'russ_options_validate'
    );
}

function russ_options_page() {
    add_options_page(
        'Russ Options',
        'Russ Options',
        'manage_options',
        'russ_options',
        'russ_render_options'
    );
}

function russ_render_options() {
    ?>
    <div class="wrap">
        <form method="post" action="options.php">
            <?php
            settings_fields( 'russ_options_group' );
            $options = get_option( 'russ_options' );
            ?>
            <table class="form-table">
                <tr valign="top"><th scope="row">Choose a page</th>
                    <td>
                        <select name="russ_options[page_id]">
                            <?php
                            if( $pages = get_pages() ){
                                foreach( $pages as $page ){
                                    echo '<option value="' . $page->ID . '" ' . selected( $page->ID, $options['page_id'] ) . '>' . $page->post_title . '</option>';
                                }
                            }
                            ?>
                        </select>
                    </td>
                </tr>
            </table>
            <p class="submit">
                <input type="submit" class="button-primary" value="<?php _e('Save Changes') ?>" />
            </p>
        </form>
    </div>
    <?php   
}

function russ_options_validate( $input ) {
    // do some validation here if necessary
    return $input;
}

Answer 2

Rather than reimplement the dropdown as @Milo suggested, it's easier to use

wp_dropdown_pages( array( 'name' => 'russ_options[page_id]', 'selected' => $options['page_id'] ) );

--as described at https://developer.wordpress.org/reference/functions/wp_dropdown_pages/