未捕获错误：调用成员函数错误消息

UPDATE 1:

I forgot to add GetTags() method, so here it is:

public $blog_tags;
public function GetTags()
{
    return $this->blog_tags;
}

=========================================================================

I'm working with PHP OOP to develop my project. Basically I have a table called blogs which contains some fields and data like this image:

capture

Then I created a class Blos.class.php and made two methods as below:

public function ShowTag()
{
    $tag = $this->_db->prepare("SELECT blog_tags FROM blogs");
    $tag->execute();
    while($row = $tag->fetch())
    {
        $this->blog_tags = $row['blog_tags'];
    }
}
public function NumTag()
{
    $cat = $this->_db->prepare("SELECT blog_tags FROM blogs");
    $cat->execute();
    $row_cat = $cat->rowCount();
    return $row_cat;
}

Then in order to retrieve data on screen, I did this:

$tagSet = new Blogs();
$tags = $tagSet->NumTag();
$tagShow = $tagSet->ShowTag();

if(!empty($tags)){
    $tagShow->GetTags();
}else{
    echo "There is no tag available right now!";
}

But the problem is I get this error message:

Fatal error: Uncaught Error: Call to a member function GetTags() on null in line 20

Which is this line:

$tagShow->GetTags();

So what is the mistake with that ? Can you please help me ?

The problem with the class function is

$tagShow = $tagSet->ShowTag(); //returns no value, hence $tagShow is null/empty.

Moreover,

$tagShow->GetTags();

GetTags() is a function which does not exist in your class. Also, you are calling the function wrong way. $tagShow is originally not an object of your class, it is a variable storing output from ShowTag().

If you have a function named GetTags(), call it using

$tagSet->GetTags();

Try using it this way:

public function ShowTag()
{
    $blog_tags=array();
    $tag = $this->_db->prepare("SELECT blog_tags FROM blogs");
    $tag->execute();
    while($row = $tag->fetch())
    {
        $blog_tags[] = $row['blog_tags'];
    }

    return $blog_tags;
}

and then in your calling,

$tagShow = $tagSet->ShowTag();

if(count($tagShow)>0){
    print_r($tagShow);   //Do whatever with the tags array.
}else{
    echo "There is no tag available right now!";
}

Try this way and see if it helps.

here your code:

  if(!empty($tags)){

    $tagShow->GetTags();

  }else{
    echo "There is no tag available right now!";
  }

there GetTags() function isn't this current class. if GetTags in this class so use $this->GetTags() .