我创建了一个自定义列表视图，它将显示我的数据库中的区域列表，但有时数据不会显示。在活动中停留几秒钟并再次重新启动活动后，它将显示列表。这是我的代码，你可以检查一下吗？如果看到问题是什么。谢谢！
AreaListActivity.java
private ListAdapter adapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_list);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
setupActionBar();
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
getSupportActionBar().setDisplayShowHomeEnabled(true);
}
@Override
protected void onResume() {
super.onResume();
setupList();
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// handle arrow click here
if (item.getItemId() == android.R.id.home) {
finish(); // close this activity and return to preview activity (if there is any)
}
return super.onOptionsItemSelected(item);
}
@Override
protected void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
// Only if you need to restore open/close state when
// the orientation is changed
if (adapter != null) {
adapter.saveStates(outState);
}
}
@Override
protected void onRestoreInstanceState(Bundle savedInstanceState) {
super.onRestoreInstanceState(savedInstanceState);
// Only if you need to restore open/close state when
// the orientation is changed
if (adapter != null) {
adapter.restoreStates(savedInstanceState);
}
}
private void setupList() {
ListView listView = (ListView) findViewById(R.id.list_view);
adapter = new ListAdapter(this, createList());
listView.setAdapter(adapter);
}
private List<String> createList() {
final List<String> list = new ArrayList<>();
Response.Listener<String> responseListener = new Response.Listener<String>() {
@Override
public void onResponse(String response) {
try {
JSONArray jsonArray = new JSONArray(response);
for (int i = 0; i < jsonArray.length(); i++) {
JSONObject obj = jsonArray.getJSONObject(i);
String areaName = obj.getString("area_name");
list.add(areaName);
}
} catch (JSONException e) {
e.printStackTrace();
}
}
};
GetAreaListRequest registerRequest = new GetAreaListRequest("True", responseListener);
RequestQueue queue = Volley.newRequestQueue(AreaListActivity.this);
queue.add(registerRequest);
return list;
}
private void setupActionBar() {
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
if (getSupportActionBar() != null) {
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
getSupportActionBar().setDisplayShowHomeEnabled(true);
toolbar.setNavigationOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
finish();
}
});
}
}
GetAreaListRequest.java
public class GetAreaListRequest extends StringRequest {
private static final String GET_AREA_LIST_URL = "http://192.168.1.7:8080/smsams/get_area_list.php";
private Map<String, String> params;
public GetAreaListRequest(String get_area_status, Response.Listener<String> listener) {
super(Method.POST, GET_AREA_LIST_URL, listener, null);
params = new HashMap<>();
params.put("get_area_status", get_area_status);
}
@Override
public Map<String, String> getParams() {
return params;
}
ListAdapter.java
class ListAdapter extends ArrayAdapter<String> {
private final LayoutInflater mInflater;
private final ViewBinderHelper binderHelper;
private Context context;
ListAdapter(Context context, List<String> objects) {
super(context, R.layout.row_list, objects);
mInflater = LayoutInflater.from(context);
binderHelper = new ViewBinderHelper();
this.context = context;
// uncomment if you want to open only one row at a time
// binderHelper.setOpenOnlyOne(true);
}
@NonNull
@Override
public View getView(int position, View convertView, @NonNull ViewGroup parent) {
final ViewHolder holder;
if (convertView == null) {
convertView = mInflater.inflate(R.layout.row_list, parent, false);
holder = new ViewHolder();
holder.textView = (TextView) convertView.findViewById(R.id.text);
holder.statView = convertView.findViewById(R.id.statistic_layout);
holder.mapView = convertView.findViewById(R.id.map_layout);
holder.infoView = convertView.findViewById(R.id.info_layout);
holder.swipeLayout = (SwipeRevealLayout) convertView.findViewById(R.id.swipe_layout);
convertView.setTag(holder);
} else {
holder = (ViewHolder) convertView.getTag();
}
final String item = getItem(position);
if (item != null) {
binderHelper.bind(holder.swipeLayout, item);
holder.textView.setText(item);
holder.statView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent i = new Intent(context, StatisticActivity.class);
context.startActivity(i);
}
});
holder.mapView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Intent i = new Intent(context, MapsActivity.class);
i.putExtra("soilArea", holder.mapView.toString());
context.startActivity(i);
}
});
holder.infoView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Intent i = new Intent(context, InfoViewActivity.class);
context.startActivity(i);
}
});
}
return convertView;
}
/**
* Only if you need to restore open/close state when the orientation is changed.
* Call this method in {@link android.app.Activity#onSaveInstanceState(Bundle)}
*/
void saveStates(Bundle outState) {
binderHelper.saveStates(outState);
}
/**
* Only if you need to restore open/close state when the orientation is changed.
* Call this method in {@link android.app.Activity#onRestoreInstanceState(Bundle)}
*/
void restoreStates(Bundle inState) {
binderHelper.restoreStates(inState);
}
private class ViewHolder {
TextView textView;
View statView;
View mapView;
View infoView;
SwipeRevealLayout swipeLayout;
}
答案 0 :(得分：1)
试试这个：
private List<String> list = new ArrayList<>();
private void setupList() {
ListView listView = (ListView) findViewById(R.id.list_view);
adapter = new ListAdapter(this, list);
listView.setAdapter(adapter);
}
private void createList() {
Response.Listener<String> responseListener = new Response.Listener<String>() {
@Override
public void onResponse(String response) {
try {
JSONArray jsonArray = new JSONArray(response);
for (int i = 0; i < jsonArray.length(); i++) {
JSONObject obj = jsonArray.getJSONObject(i);
String areaName = obj.getString("area_name");
list.add(areaName);
}
adapter.notifyDataSetChanged();
} catch (JSONException e) {
e.printStackTrace();
}
}
};
GetAreaListRequest registerRequest = new GetAreaListRequest("True", responseListener);
RequestQueue queue = Volley.newRequestQueue(AreaListActivity.this);
queue.add(registerRequest);
}
答案 1 :(得分：0)
网络请求通常以异步方式发生。因此没有特定的时间来调用onResponse()。因此，在createList()方法中，您初始化了一个空的arraylist，并在请求生成响应之前（异步调用onResponse）返回不包含任何值的列表。
您可以更改类似的代码：
在createList()：
Response.Listener<String> responseListener = new Response.Listener<String>() {
@Override
public void onResponse(String response) {
try {
JSONArray jsonArray = new JSONArray(response);
for (int i = 0; i < jsonArray.length(); i++) {
JSONObject obj = jsonArray.getJSONObject(i);
String areaName = obj.getString("area_name");
list.add(areaName);
adapter = new ListAdapter(this, list);
listView.setAdapter(adapter);
}
} catch (JSONException e) {
e.printStackTrace();
}
}
};
所以这里只有在从网络中提取数据后才设置适配器。