public class GraphFrameV2 extends Fragment implements AdapterView.OnItemSelectedListener {
Integer hoodSelector = 27;
ArrayList<HoodData> hoodDataList = new ArrayList<>();
ArrayList<String> hoodList = new ArrayList<>();
ArrayList<HoodData> completeHoodList = new ArrayList<>();
@Override
public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
String item = parent.getItemAtPosition(position).toString();
// Showing selected spinner item
for(int i = 1; i < hoodList.size(); i++) {
if (item.equals(hoodList.get(i))) {
setHoodId(i + 27);
refreshFragment();
}
}
}
public Double calculateMax(Integer year){
Double max = completeHoodList.get(0).getPercentage();
if(year == 2006){
for(Integer z = 0; z < completeHoodList.size(); z ++){
if(completeHoodList.get(z).getYear() == 2006){
if(completeHoodList.get(z).getPercentage() > max){
max = completeHoodList.get(z).getPercentage();
}
}
}
}
Toast.makeText(getActivity(), String.valueOf(max),
Toast.LENGTH_LONG).show();
return max;
}
public void calculateMin(Integer year){
Double min = completeHoodList.get(0).getPercentage();
if(year == 2006){
for(Integer z = 0; z < completeHoodList.size(); z ++){
if(completeHoodList.get(z).getYear() == 2006){
if(completeHoodList.get(z).getPercentage() < min){
min = completeHoodList.get(z).getPercentage();
}
}
}
}
if(year == 2007){
for(Integer z = 0; z < completeHoodList.size(); z ++){
if(completeHoodList.get(z).getYear() == 2007){
if(completeHoodList.get(z).getPercentage() < min){
min = completeHoodList.get(z).getPercentage();
}
}
}
}
if(year == 2008){
for(Integer z = 0; z < completeHoodList.size(); z ++){
if(completeHoodList.get(z).getYear() == 2008){
if(completeHoodList.get(z).getPercentage() < min){
min = completeHoodList.get(z).getPercentage();
}
}
}
}
if(year == 2009){
for(Integer z = 0; z < completeHoodList.size(); z ++){
if(completeHoodList.get(z).getYear() == 2009){
if(completeHoodList.get(z).getPercentage() < min){
min = completeHoodList.get(z).getPercentage();
}
}
}
}
if(year == 2011){
for(Integer z = 0; z < completeHoodList.size(); z ++){
if(completeHoodList.get(z).getYear() == 2011){
if(completeHoodList.get(z).getPercentage() < min){
min = completeHoodList.get(z).getPercentage();
}
}
}
}
}
public Double calculateAvg(Integer year){
Double avg = null;
Double sum = 0.0;
Integer counter = 0;
if(year == 2006){
for(Integer z = 0; z < completeHoodList.size(); z++){
if(completeHoodList.get(z).getYear() == 2006){
sum = sum + completeHoodList.get(z).getPercentage();
counter = counter + 1;
}
}
}
return Math.round((sum/counter) * Math.pow(10, 1)) / Math.pow(10, 1);
}
@Override
public void onNothingSelected(AdapterView<?> parent) {
}
public void refreshFragment(){
//refreshes the Fragment
hoodDataList.clear();
FragmentTransaction transaction = getFragmentManager().beginTransaction();
transaction.detach(this).attach(this).commit();
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
final View view = inflater.inflate(R.layout.fragment_graph,
container, false);
//API Request for all the hoods
getAllData();
getDataFromApi((GraphView) view.findViewById(R.id.graph));
getDataForSpinner((Spinner) view.findViewById(R.id.spinner));
return view;
}
public void setHoodId(Integer hood){
hoodSelector = hood;
}
public void getAllData(){
RequestQueue rq = Volley.newRequestQueue(getActivity().getApplicationContext());
String url= "http://test.dontstealmywag.ga/api/theft_outof_car_wijk.php";
StringRequest stringRequest = new StringRequest(Request.Method.GET, url,
new Response.Listener<String>() {
@Override
public void onResponse(String response) {
// Do something with the response
try{
JSONObject o = new JSONObject(response);
JSONArray values=o.getJSONArray("");
for (int i = 0; i < values.length(); i++) {
JSONObject jsonObject = values.getJSONObject(i);
completeHoodList.add(new HoodData(jsonObject.getDouble("percentage"), jsonObject.getInt("hood_id"), jsonObject.getInt("year"), jsonObject.getString("hood_name")));
}
} catch (JSONException ex){}
}
},
new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
// Handle error
}
});
rq.add(stringRequest);
}
public void getDataFromApi(final GraphView graph) {
RequestQueue rq = Volley.newRequestQueue(getActivity().getApplicationContext());
String url= "http://test.dontstealmywag.ga/api/theft_outof_car_wijk.php?hood_id=" + hoodSelector;
StringRequest stringRequest = new StringRequest(Request.Method.GET, url,
new Response.Listener<String>() {
@Override
public void onResponse(String response) {
// Do something with the response
try{
JSONObject o = new JSONObject(response);
JSONArray values=o.getJSONArray("");
for (int i = 0; i < values.length(); i++) {
JSONObject jsonObject = values.getJSONObject(i);
hoodDataList.add(new HoodData(jsonObject.getDouble("percentage"), jsonObject.getInt("hood_id"), jsonObject.getInt("year"), jsonObject.getString("hood_name")));
}
} catch (JSONException ex){}
StaticLabelsFormatter staticLabelsFormatter = new StaticLabelsFormatter(graph);
LineGraphSeries<DataPoint> series = new LineGraphSeries<>(new DataPoint[] {
new DataPoint(1, (calculateAvg(2006 /2))),
new DataPoint(2, hoodDataList.get(1).getPercentage()),
new DataPoint(3, hoodDataList.get(2).getPercentage()),
new DataPoint(4, hoodDataList.get(3).getPercentage()),
new DataPoint(5, hoodDataList.get(4).getPercentage())
//new DataPoint(12, 0)
});
LineGraphSeries<DataPoint> average = new LineGraphSeries<>(new DataPoint[]{
new DataPoint(1, 16.2),
new DataPoint(2, 15.5),
new DataPoint(3, 15.2),
new DataPoint(4, 15.9),
new DataPoint(5, 13.9)
});
// set manual x bounds
staticLabelsFormatter.setHorizontalLabels(new String[] {"2006", "2007","2008","2009","2011"});
//creates custom x-axis
graph.getGridLabelRenderer().setLabelFormatter(staticLabelsFormatter);
graph.setTitle("Wijk " + hoodSelector + " - " + hoodDataList.get(0).getHood_name());
//set nice background color :)
series.setDrawBackground(true);
//shows points at datapoints
series.setDrawDataPoints(true);
average.setDrawDataPoints(true);
//size of the points
series.setDataPointsRadius(10.0f);
series.setOnDataPointTapListener(new OnDataPointTapListener() {
@Override
public void onTap(Series series, DataPointInterface dataPoint) {
Toast.makeText(getActivity(), "Punt "+ dataPoint, Toast.LENGTH_SHORT).show();
}
});
series.setTitle("%");
series.setAnimated(true);
average.setAnimated(true);
average.setColor(Color.argb(255, 0, 51, 153));
average.setThickness(5);
series.setColor(Color.argb(255, 102, 204, 255));
graph.addSeries(average);
graph.getLegendRenderer().setVisible(true);
graph.getLegendRenderer().setAlign(LegendRenderer.LegendAlign.TOP);
graph.addSeries(series);
}
},
new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
// Handle error
}
});
rq.add(stringRequest);
}
public void getDataForSpinner(final Spinner spinner){
RequestQueue rq = Volley.newRequestQueue(getActivity().getApplicationContext());
String url= "http://test.dontstealmywag.ga/api/theft_outof_car_wijk.php";
StringRequest stringRequest = new StringRequest(Request.Method.GET, url,
new Response.Listener<String>() {
@Override
public void onResponse(String response) {
// Do something with the response
try{
JSONObject o = new JSONObject(response);
JSONArray values=o.getJSONArray("");
for (int i = 0; i < values.length(); i++) {
JSONObject jsonObject = values.getJSONObject(i);
if (!hoodList.contains(jsonObject.getString("hood_name"))) {
hoodList.add(jsonObject.getString("hood_name"));
}
}
} catch (JSONException ex){}
ArrayAdapter<String> adapter = new ArrayAdapter<String>(spinner.getContext(), android.R.layout.simple_spinner_item, hoodList);
// Specify the layout to use when the list of choices appears
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
// Apply the adapter to the spinner
spinner.setPrompt("Title");
spinner.setAdapter(adapter);
spinner.setOnItemSelectedListener(GraphFrameV2.this);
}
},
new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
// Handle error
}
});
rq.add(stringRequest);
}
}
问题:
这段代码是我写的。当我在 getAllData 中调用 calculateMax(2006) 时，它工作正常，并为我提供了我想要的 toast，但是当我在 getDataFromApi 中调用它时，应用程序崩溃了，告诉我我的列表不包含任何项目。
这很奇怪，因为我的 calculateAvg() 方法确实有效。
谁能帮我解决这个问题吗？
最佳答案
该问题与网络请求本质上是异步的这一事实有关。
假设有3个同步 Action (A、B、C)
Start A
Complete A
Start B
Complete B
Start C
Complete C
如果 B 是异步的，则可能会发生这种情况
Start A
Complete A
Start B (async)
Start C (maybe C need the result from B, but unfortunately B is still running, on another thread)
Complete C
Complete B
因此，如果您的下一个操作需要异步操作的结果，您基本上必须等到异步操作完成。
为此，您需要在回调 onResponse() 中执行下一个操作。只有这里的数据可用。
关于java - 从 ArrayList 计算最大值不起作用，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/43503280/