Android: cannot refresh Listview using CustomAdapter

问题

I need to refresh the list view with new data. This code below is used to obtain data in OnCreateView that is in FragmentActivity at the first time.

override fun onCreateView(inflater: LayoutInflater?, container: ViewGroup?,
                          savedInstanceState: Bundle?): View? {
        val url = "something"

        val request_queue = Volley.newRequestQueue(this.context)
        val stringRequest = StringRequest(Request.Method.GET, url,
                Response.Listener<String> { response ->
                    val pending_job = Gson().fromJson<ArrayList<HashMap<String, String>>>(
                            response.toString(),
                            object : TypeToken<ArrayList<HashMap<String, String>>>() {}.type
                    )
                    this@PlaceholderFragment.showList(rootView, R.id.pending_job_list, pending_job)

                    pending_job_list_layout.setOnRefreshListener(this)

                    request_queue.stop()
                }, Response.ErrorListener { error ->
            if (error.networkResponse != null) {
                Toast.makeText(this.context, error.networkResponse.statusCode.toString(), Toast.LENGTH_SHORT).show()
            }
            request_queue.stop()
        })
        request_queue.add(stringRequest)
}

showList is the function to set CustomAdapter, which is

fun showList(rootView: View, tab_id: Int, job_list: ArrayList<HashMap<String, String>>) {

    // custom display ListView
    val adapter: CustomAdapter = CustomAdapter(
            this.context,
            job_list
    )

    this_adapter = adapter

    val listView = rootView.findViewById(tab_id) as ListView
    listView.adapter = adapter
}

, and this CustomAdapter class,

class CustomAdapter(internal var mContext: Context,
                internal var job_list: ArrayList<HashMap<String, String>>
                ) : BaseAdapter() {

override fun getCount(): Int {
    return job_list.size
}

override fun getItem(position: Int): Any? {
    return null
}

override fun getItemId(position: Int): Long {
    return 0
}

override fun getView(position: Int, view: View?, parent: ViewGroup): View {
    val mInflater = mContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE) as LayoutInflater

    val item_view = mInflater.inflate(R.layout.activity_job_item, parent, false)

    val job_name: MutableList<String> = arrayListOf()
    job_list.mapTo(job_name) { it["BaseSiteName"] as String }
    val nameView: TextView = item_view.findViewById(R.id.name) as TextView
    nameView.text = job_name[position]

    val job_date: MutableList<String> = arrayListOf()
    job_list.mapTo(job_date) { it["PlanDt"] as String}
    val dateView: TextView = item_view.findViewById(R.id.date) as TextView
    dateView.text = job_date[position]

    item_view.setOnClickListener{
        val intent: Intent = Intent(mContext, JobDetailActivity::class.java)
        intent.putExtra("job", job_list[position])
        mContext.startActivity(intent)
    }

    return item_view
}

}

However, I want to make the list refresh-able. I've written the following code to refresh the list.

override fun onRefresh() {
    Toast.makeText(this.context, "Refresh", Toast.LENGTH_SHORT).show()
    val rootView = this_inflater!!.inflate(R.layout.fragment_pending_job, this_container, false)

    val url = "something"

    val request_queue = Volley.newRequestQueue(this.context)
    val stringRequest = StringRequest(Request.Method.GET, url,
            Response.Listener<String> { response ->
                val pending_job = Gson().fromJson<ArrayList<HashMap<String, String>>>(
                        response.toString(),
                        object : TypeToken<ArrayList<HashMap<String, String>>>() {}.type
                )

                val adapter: CustomAdapter = CustomAdapter(
                        this.context,
                        pending_job
                )

                val listView = rootView.findViewById(R.id.pending_job_list) as ListView
                listView.adapter = adapter

                pending_job_list_layout.isRefreshing = false

                pending_job_list_layout.setOnRefreshListener(this)

                request_queue.stop()
            }, Response.ErrorListener { error ->
        if (error.networkResponse != null) {
            Toast.makeText(this.context, error.networkResponse.statusCode.toString(), Toast.LENGTH_SHORT).show()
        }
        request_queue.stop()
    })
    request_queue.add(stringRequest)
}

That is just instantiating the CustomAdapter again and take it to the listview again.

When I refresh, nothing in the list is changed.

回答1:

Define a method UpdateData in CustomAdapter class which will receive new data and replaces old data

fun UpdateData(new_job_list: ArrayList<HashMap<String, String>>){
       job_list.clear()
       job_list.addAll(new_job_list)
       notifyDataSetChanged()
   }

Now when you get new data from volly, instead of setting adapter again for listview just use

adapter.UpdateData(pending_job)

回答2:

1.Way: You can make background listener with Asynctask .You can listen to your server in a loop continuous.When data changed than you can refresh the listview.This way is easy but not good for performance.

2.Way: You can use firebase database.Because it is working realtime.

3.Way: If you don't want change your database.You can use Google Cloud Messaging.You must implement this, both server and your application.When data changed on server listen and send message with cloud messaging to android app.And refresh list view automatically.

来源：https://stackoverflow.com/questions/42065482/android-cannot-refresh-listview-using-customadapter