java - Android Arraylist迭代根据是否存在设置或添加

Question

我希望能够根据其 _sensor_id 检查对象是否存在于 ArrayList 中，该对象显示在 ListView 中。

如果存在，我想设置它，如果不存在，我想添加它。每次此方法运行时，HashMap 数据都会不同，我希望它根据_sensor_id 检查它是否存在于ListView(ArrayList) 中。

if (mEquipmentList.isEmpty()) {
 // Populate the Equipment List
 HashMap < String, String > equip = new HashMap < String, String > ();
 equip.put(FIRST_COLUMN, _sensor_id);
 equip.put(THIRD_COLUMN, Double.toString(_speed) + "km/h");
 equip.put(FOURTH_COLUMN, Double.toString(_heading) + "°");
 equip.put(FIFTH_COLUMN, Double.toString(distance) + "m");
 equip.put(SECOND_COLUMN, Double.toString(mEquipmentList.indexOf(equip)));
 mEquipmentList.add(equip);

 for (HashMap < String, String > entry: mEquipmentList) {
  for (String key: entry.keySet()) {
   String value = entry.get(key);
   //Debugging
   Log.d("equipment contains= ", "sensorid: " + mEquipmentList.get(0));
   Log.d("equipment key = ", "key: " + key);
   Log.d("equipment value = ", "value: " + value);
   Log.d("equipment index", "value:" + (mEquipmentList.indexOf(equip)));
  }
 }
} else {

 // Populate the Equipment List
 HashMap < String, String > equip = new HashMap < String, String > ();
 equip.put(FIRST_COLUMN, _sensor_id);
 equip.put(THIRD_COLUMN, Double.toString(_speed) + "km/h");
 equip.put(FOURTH_COLUMN, Double.toString(_heading) + "°");
 equip.put(FIFTH_COLUMN, Double.toString(distance) + "m");
 equip.put(SECOND_COLUMN, Double.toString(mEquipmentList.size()));
 mEquipmentList.set(0, equip);

 for (HashMap < String, String > entry: mEquipmentList) {
  for (String key: entry.keySet()) {
   String value = entry.get(key);
   //Debugging
   Log.d("equipment contains= ", "sensorid: " + mEquipmentList);
   Log.d("equipment contains= ", "sensorid: " + mEquipmentList.contains(key));
   Log.d("equipment key = ", "key: " + key);
   Log.d("equipment value = ", "value: " + value);
   Log.d("equipment index", "value:" + mEquipmentList.indexOf(equip));
  }
 }
}

// Set the adapter
ListViewAdapter adapter = new ListViewAdapter(this, mEquipmentList);
listView.setAdapter(adapter);
adapter.notifyDataSetChanged();

}

编辑 *********

  public void updateEquipList(String message) {

    if (!pathHistory.isEmpty()) {
        double currentLat = pathHistory.getFirst().lat;
        double currentLng = pathHistory.getFirst().lng;
        int currentOrientation = getResources().getConfiguration().orientation;

        ListView listView = (ListView) findViewById(R.id.equip_list);

        HashMap<String, Equipment> equipmentMap = new HashMap<String, Equipment>();

        try {
            List<String> data_list = Arrays.asList(message.split(","));

            // point added (checks in correct format)
            String _sensor_id = data_list.get(0);
            if (_sensor_id.substring(0, Math.min(_sensor_id.length(), 2)).equals("DT")) {

                double _lat = Double.parseDouble(data_list.get(3));
                double _lng = Double.parseDouble(data_list.get(4));
                double _heading = Double.parseDouble(data_list.get(5));
                double _speed = Double.parseDouble(data_list.get(6));
                int distance = (int) Trajectory.ChordLength(currentLat, currentLng, _lat, _lng);
                boolean doesSensorExist = false;

                // for input _sensor_id, check if there exists an Equipment object in map.
                Equipment equip = equipmentMap.get(_sensor_id);
                if(equip == null) // no object for this sensor_id
                {
                    equip = new Equipment();
                    // populate equipment attributes in the object
                    equip.addParameter(THIRD_COLUMN, Double.toString(_speed) + "km/h");
                    equip.addParameter(FOURTH_COLUMN, Double.toString(_heading) + "°");
                    equip.addParameter(FIFTH_COLUMN, Double.toString(distance) + "m");
                    equip.addParameter(SECOND_COLUMN, Double.toString(mEquipmentList.indexOf(equip)));

                    // add this Equipment Object in the map.
                    equipmentMap.put(_sensor_id, equip);
                    /// since its a new object, add same to the  mEquipmentList which is a unique array of Equipment Object
                    mEquipmentList.add(equip);
                }
                else // Equipment object exits for input _sensor_id string
                {
                    //Update the values for eq object if they are changed
                    equip.addParameter(THIRD_COLUMN, Double.toString(_speed) + "km/h");
                    equip.addParameter(FOURTH_COLUMN, Double.toString(_heading) + "°");
                    equip.addParameter(FIFTH_COLUMN, Double.toString(distance) + "m");
                    equip.addParameter(SECOND_COLUMN, Double.toString(mEquipmentList.indexOf(equip)));
                    // here no need to add the Equipment Object in the ArrayList again.
                }

                // Set the adapter
                ListViewAdapter adapter = new ListViewAdapter(this, mEquipmentList);
                listView.setAdapter(adapter);

                }
            } catch(Exception e){
                // Marker construction failed
                Log.d(TAG, "Updating list failed: " + e.toString());
            }
        }

    }

class Equipment extends HashMap<String, String> {
    HashMap<String, String> parameters;

    void addParameter(String key, String value)
    {
        parameters.put(key, value);
    }
}

ListView 适配器

公共(public)类 ListViewAdapter 扩展 BaseAdapter {

public ArrayList<com.bhp.prox_aware.MapsActivity.Equipment> list;
Activity MapsActivity;
TextView txtFirst;
TextView txtSecond;
TextView txtThird;
TextView txtFourth;
TextView txtFifth;

public ListViewAdapter(Activity activity, ArrayList<com.bhp.prox_aware.MapsActivity.Equipment> list){
    super();
    this.MapsActivity=activity;
    this.list=list;
}

@Override
public int getCount() {
    // TODO Auto-generated method stub
    return list.size();
}

@Override
public Object getItem(int position) {
    // TODO Auto-generated method stub
    return list.get(position);
}

@Override
public long getItemId(int position) {
    // TODO Auto-generated method stub
    return 0;
}



@Override
public View getView(int position, View convertView, ViewGroup parent) {
    // TODO Auto-generated method stub

    LayoutInflater inflater=MapsActivity.getLayoutInflater();

    if(convertView == null){

        convertView=inflater.inflate(R.layout.equip_row, null);


        /* TODO add an ImageView here for an icon to display next to the list  */
        txtFirst=(TextView) convertView.findViewById(R.id.name);
        txtSecond=(TextView) convertView.findViewById(R.id.id);
        txtThird=(TextView) convertView.findViewById(R.id.speed);
        txtFourth=(TextView) convertView.findViewById(R.id.direction);
        txtFifth=(TextView) convertView.findViewById(R.id.distance);
    }

    int color = Color.argb( 200, 34, 34, 34 );


    HashMap<String, String> map=list.get(position);
    txtFirst.setText(map.get(FIRST_COLUMN));
    txtSecond.setText(map.get(SECOND_COLUMN));
    txtThird.setText(map.get(THIRD_COLUMN));
    txtFourth.setText(map.get(FOURTH_COLUMN));
    txtFifth.setText(map.get(FIFTH_COLUMN));

    //Check if within 100m if yes change colour of background to red
    double distanceCheck = Double.parseDouble(map.get(FIFTH_COLUMN).replace("m", ""));
    if(distanceCheck <= 100){

        color = Color.argb( 200, 163, 0, 0 );
    }else {
        color = Color.argb(200, 34, 34, 34);
    }

    txtFirst.setTextColor(Color.WHITE);
    txtFirst.setBackgroundColor( color );

    txtSecond.setTextColor(Color.WHITE);
    txtSecond.setBackgroundColor( color );

    txtThird.setTextColor(Color.WHITE);
    txtThird.setBackgroundColor( color );

    txtFourth.setTextColor(Color.WHITE);
    txtFourth.setBackgroundColor( color );

    txtFifth.setTextColor(Color.WHITE);
    txtFifth.setBackgroundColor( color );

    return convertView;
}

}

Answer 1

您应该能够以稍微不同的方式对代码结构进行建模如果可能的话，创建一个类，例如设备，其属性用于将列参数(如速度、温度等)存储为字符串映射，字符串该类

class Equipment
{
  HashMap<String, String> parameters;

  void addParameter(String key, String value)
  {
    parameters.put(key, value);
  }
}

在您的逻辑中，sensor_id 是保持 Equipment 对象唯一性的关键。因此创建一个字符串和设备的映射

HashMap<String, Equipment> equipmentMap = new HashMap<String, Equipment>();
// for input _sensor_id, check if there exists an Equipment object in map. 
 Equipment equip = sensorMap.get(_sensor_id);
if(equip == null) // no object for this sensor_id
{
  equip = new Equipment(); 
  // populate equipment attributes in the object 
   equip.addParameter(THIRD_COLUMN, Double.toString(_speed) + "km/h");
   equip.addParameter(FOURTH_COLUMN, Double.toString(_heading) + "°");
   equip.addParameter(FIFTH_COLUMN, Double.toString(distance) + "m");
   equip.addParameter(SECOND_COLUMN, Double.toString(mEquipmentList.indexOf(equip)));

   // add this Equipment Object in the map.
   sensorMap.put(_sensor_id, equip); 
 /// since its a new object, add same to the  mEquipmentList which is a unique array of Equipment Object
  mEquipmentList.add(eq);
}
else // Equipment object exits for input _sensor_id string
{
   //Update the values for eq object if they are changed
  equip.addParameter(THIRD_COLUMN, Double.toString(_speed) + "km/h");
   equip.addParameter(FOURTH_COLUMN, Double.toString(_heading) + "°");
   equip.addParameter(FIFTH_COLUMN, Double.toString(distance) + "m");
   equip.addParameter(SECOND_COLUMN, Double.toString(mEquipmentList.indexOf(equip)));

   // here no need to add the Equipment Object in the ArrayList again.
}
// notify adapter for data change
adapter.notifyDataSetChanged();

HashMap 有助于根据 _sensor_id 保持数据的唯一性。

希望这有帮助..