Gelöst: Ich habe einen Adapter basierend auf dem Vorschlag von @JJV erstellt. Ich bin mir bewusst, dass es viel Raum für Verbesserungen gibt, aber es funktioniert vorerst. Ich habe diese vereinfachte Version meines Programms mit dem Arbeitscode aktualisiert. Ich hoffe, es wird für andere nützlich sein:

MainActivity.java:

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.widget.ListAdapter;
import android.widget.ListView;

import java.util.Map;
import java.util.TreeMap;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main_activity);

        Map<Integer, Object> m = new TreeMap<Integer, Object>();

        int key = 123;
        Item obj1 = new Item("abc", "xyz", 888);
        m.put(key, obj1);

        key = 456;
        Item obj2 = new Item("def", "zyx", 999);
        m.put(key, obj2);

        ListAdapter adapter = new TreeMapAdapter(this, (TreeMap<Integer, Object>) m);
        ListView itemListView = (ListView) findViewById(R.id.itemListView);
        itemListView.setAdapter(adapter);
    }

    public class Item {
        private String name;
        private String thing;
        private int number;

        Item(String name, String thing, int number) {
            this.name = name;
            this.thing = thing;
            this.number = number;
        }

        public String getName() {
            return this.name;
        }

        public String getThing() {
            return this.thing;
        }

        public int getNumber() {
            return this.number;
        }
    }
}

main_activity.xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">

    <ListView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/itemListView" />
</LinearLayout>

listview_row.xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="horizontal" android:layout_width="match_parent"
    android:layout_height="match_parent">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceMedium"
        android:id="@+id/name" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceMedium"
        android:id="@+id/thing" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceMedium"
        android:id="@+id/number" />
</LinearLayout>

TreeMapAdapter.java:

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.TextView;

import java.util.TreeMap;


public class TreeMapAdapter extends ArrayAdapter<String> {

    private Context context;
    private TreeMap<Integer, Object> treeMap;
    private Integer[] mapKeys;

    public TreeMapAdapter(Context context, TreeMap<Integer, Object> data) {
        super(context, R.layout.listview_row);

        this.context = context;
        this.treeMap = data;
        mapKeys = treeMap.keySet().toArray(new Integer[getCount()]);
    }

    public int getCount() {
        return treeMap.size();
    }

    public String getItem(int position) {
        return String.valueOf(treeMap.get(mapKeys[position]));
    }

    public long getItemId(int position) {
        return mapKeys[position];
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        LayoutInflater deviceInflater = LayoutInflater.from(getContext());
        View listViewRow = deviceInflater.inflate(R.layout.listview_row, parent, false);

        MainActivity.Item test = (MainActivity.Item) treeMap.get(mapKeys[position]);

        String nameString = test.getName() + ", ";
        String thingString = test.getThing() + ", ";
        String numberInt = String.valueOf(test.getNumber());

        TextView name = (TextView) listViewRow.findViewById(R.id.name);
        TextView thing = (TextView) listViewRow.findViewById(R.id.thing);
        TextView number = (TextView) listViewRow.findViewById(R.id.number);

        name.setText(nameString);
        thing.setText(thingString);
        number.setText(numberInt);

        return listViewRow;
    }

}

Ergebni: Ich kann keinen Screenshot des Ergebnisses in diesen Beitrag einbetten, da ich keine Reputation von 10 habe, aber das Ergebnis der Ausführung des Codes können Sie hier sehen:http: //i.stack.imgur.com/QoXX1.pn