ListView不可见

Question

我从MySQL数据库中获取元素并将它们输入到ListView中。 ListView中的arraylist获取元素，但ListView不会显示在屏幕上。这是代码：

String name, url;
final List<String> myContacts = new ArrayList<String>();
RequestQueue requestQueue;
private ListView listView;

protected void onCreate(Bundle savedInstanceState){
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main_inbox);
    listView = (ListView) findViewById(R.id.myMessages);
    url = Values.baseUrl + "getData.php?sender=" + Values.sender;
    System.out.println(url);
    requestQueue = Volley.newRequestQueue(getApplicationContext());
    JsonObjectRequest jsonObjectRequest = new JsonObjectRequest(url, new Response.Listener<JSONObject>() {
        @Override
        public void onResponse(JSONObject response) {
            System.out.println(response.toString());
            try {
                JSONArray details = response.getJSONArray("result");
                for (int i = 0; i < details.length(); i++) {
                    JSONObject detail = details.getJSONObject(i);
                    myContacts.add(detail.getString("receiver"));
                    System.out.println(myContacts.get(i));
                }
            } catch (JSONException e) {
                e.printStackTrace();
            }
        }
    }, new Response.ErrorListener() {
        @Override
        public void onErrorResponse(VolleyError error) {
            System.out.append(error.getMessage());
        }
    });
    requestQueue.add(jsonObjectRequest);
    ArrayAdapter<String> arrayAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, myContacts);
    listView.setAdapter(arrayAdapter);
    listView.setOnItemClickListener(this);
}

public void onItemClick(AdapterView<?> parent, View view, int pos, long id) {
    try {
        String output = myContacts.get(pos).toString().trim();
        System.out.println(output);
        Values.receiver = output;
        Intent intent = new Intent(AllMessages.this, CreateMessage.class);
        startActivity(intent);
    } catch (Exception e) {
        e.printStackTrace();
    }
}

public void goToAdd(View view){
    Intent intent = new Intent(AllMessages.this, AddContact.class);
    startActivity(intent);
}

这是布局文件 - activity_main_inbox：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent">

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/viewText"
    android:textSize="10pt"
    android:layout_marginTop="20dp"
    android:layout_marginLeft="10dp"
    android:text="Inbox"/>

<ListView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/myMessages"
    android:layout_marginTop="20dp"></ListView>

<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Add"
    android:onClick="goToAdd"
    android:layout_marginTop="20dp"/>

</LinearLayout>

日志显示：

V/ActivityThread: updateVisibility : ActivityRecord{2942f886 token=android.os.BinderProxy@4e99420 {com.example.farhaan.test/com.example.farhaan.test.MainActivity}} show : false

我该如何解决这个问题？