WordPress功能switch_to_blog() 需要一个整数作为输入参数。您可以在法典中了解更多信息：

http://codex.wordpress.org/Function_Reference/switch_to_blog

请尝试这种结构：

// Get the current blog id
$original_blog_id = get_current_blog_id(); 

// All the blog_id\'s to loop through
$bids = array( 1, 2 ); 

foreach( $bids as $bid )
{
    // Switch to the blog with the blog_id $bid
    switch_to_blog( $bid ); 

    // ... your code for each blog ...
}

// Switch back to the current blog
switch_to_blog( $original_blog_id ); 

更新：如果要从每个博客的不同类别获取帖子，可以使用以下示例：

// Get current blog
$original_blog_id = get_current_blog_id(); 

// Setup a category slug for each blog id, you want to loop through - EDIT
$catslug_per_blog_id = array( 
    1 => \'video\',
    4 => \'news\' 
); 

foreach( $catslug_per_blog_id as $bid => $catslug )
{
    // Switch to the blog with the blog id $bid
    switch_to_blog( $bid ); 

    // ... your code for each blog ...
    $myposts = get_posts( 
        array( 
            \'category_name\'  => $catslug,
            \'posts_per_page\' => 10, 
        )
    );
    // ... etc
}

// Switch back to the current blog
switch_to_blog( $original_blog_id ); 

示例：下面是一个允许您使用模板标记的示例（这适用于我的多站点安装）：

// Get current blog
$original_blog_id = get_current_blog_id();

// Setup a category for each blog id you want to loop through - EDIT
$catslug_per_blog_id = array( 
    1 => \'video\',
    4 => \'news\' 
); 

foreach( $catslug_per_blog_id as $bid => $catslug )
{
    //Switch to the blog with the blog id $bid
    switch_to_blog( $bid ); 

    // Get posts for each blog
    $myposts = get_posts( 
        array( 
            \'category_name\'  => $catslug,
            \'posts_per_page\' => 2, 
        )
    );

    // Skip a blog if no posts are found
    if( empty( $myposts ) )
        continue;

    // Loop for each blog
    $li = \'\';
    global $post;
    foreach( $myposts as $post )
    {
        setup_postdata( $post );
        $li .= the_title(
            $before = sprintf( \'<li><a href="%s">\', esc_url( get_permalink() ) ),
            $after  = \'</a></li>\',
            $echo   = false
        );
    }

    // Print for each blog
    printf(
        \'<h2>%s (%s)</h2><ul>%s</ul>\',
        esc_html( get_bloginfo( \'name\' ) ),
        esc_html( $catslug ),
        $li  
    );
}

// Switch back to the current blog
switch_to_blog( $original_blog_id ); 

wp_reset_postdata();

下面是上面示例的演示屏幕截图，站点1名为贝多芬，站点4名为巴赫：

PS：感谢@brasofilo提供link 这澄清了我对restore_current_blog() ;-)

PPS：感谢@ChristineCooper分享以下评论：

只是一个友好的警告。确保不要将原始博客id设置为变量$blog_id -- 这是因为在switch_to_blog() 过程$blog_id 将被核心函数覆盖，这意味着当您尝试切换回原始博客时，最终将切换到循环通过的最后一个博客。有点让人困惑。：）