PHP method to determine whether json object exists

In the actual test, when PHP reads the json array and uses simple if or array_key_exists to determine whether the object exists, an error will be reported. The following is the correct judgment method from Google search

In fact, the error is reported because I am not very proficient in PHP, so maybe the correct judgment method I think is not the most perfect solution or even wrong. This blog post is reserved for my own use

Error code:

<span style="color: #800080;">$structure</span> = <span style="color: #008080;">imap_fetchstructure</span>(<span style="color: #800080;">$connection</span>, <span style="color: #800080;">$id</span>,<span style="color: #000000;"> FT_UID);
</span><span style="color: #0000ff;">if</span> (<span style="color: #008080;">array_key_exists</span>('parts', <span style="color: #800080;">$structure</span><span style="color: #000000;">))
{
}</span>

An error message Warning: array_key_exists() expects parameter 2 to be array, boolean given

The correct solution is:

<span style="color: #0000ff;">if</span> (<span style="color: #008080;">is_array</span>(<span style="color: #800080;">$structure</span>) && <span style="color: #008080;">array_key_exists</span>('parts', <span style="color: #800080;">$structure</span>)) <br>{ <span style="color: #008000;">//</span><span style="color: #008000;">...magic stuff here <br>}</span>

Another way is to use isset to judge directly:

<span style="color: #0000ff;">if</span>(<span style="color: #0000ff;">isset</span>(<span style="color: #800080;">$structure</span>['parts'<span style="color: #000000;">]))
 {
 }<br></span>

　 //This function is used to test whether the variable has been configured. Returns true if the variable already exists. Otherwise a false value is returned.

// Therefore, it is necessary to return TURE

if the variable exists and the value is not NULL.