我正在构建一个公交车位置应用程序。我试图从微调器中获取选定的值。请注意，微调器是从DB填充的，但是，当我尝试获取微调器的选定值时，我的应用程序崩溃了。我想从微调器中获取所选值并将其发送到我的数据库。
public class
DriversLocationUpdate extends AppCompatActivity implements AdapterView.OnItemSelectedListener{
ArrayList<String> listitems1= new ArrayList<> ();
ArrayAdapter<String> adapter1;
ArrayList<String> listitems2= new ArrayList<> ();
ArrayAdapter<String> adapter2;
Spinner busListArray, locationListArray;
ProgressBar progressbar;
Button btnUpd;
String currselectedBus, logstatus, currselectedLocat;
TextView vtxtValidation;
TextView res1,res2;
//String[] arrayUserinfo;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_drivers_location_update);
progressbar = (ProgressBar) findViewById(R.id.loginprogress);
res1=(TextView) findViewById(R.id.spin1);
res2=(TextView) findViewById(R.id.spin2);
busListArray = (Spinner) findViewById(R.id.bus_arrays);
adapter1 = new ArrayAdapter<>(this, R.layout.support_simple_spinner_dropdown_item, listitems1);
busListArray.setAdapter(adapter1);
locationListArray = (Spinner) findViewById(R.id.location_arrays) ;
adapter2 = new ArrayAdapter<>(this, R.layout.support_simple_spinner_dropdown_item, listitems2);
locationListArray.setAdapter(adapter2);
busListArray.setOnItemSelectedListener(this);
locationListArray.setOnItemSelectedListener(this);
btnUpd = (Button) findViewById(R.id.btnLocUpdt);
btnUpd.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
currselectedBus=res1.getText().toString();
currselectedLocat=res2.getText().toString();
new LocationUpdateClass().execute( currselectedBus, currselectedLocat);
}
});
}
protected void onStart(){
super.onStart();
backTask1 bt1 = new backTask1();
bt1.execute();
backTask2 bt2 = new backTask2();
bt2.execute();
}
private class backTask1 extends AsyncTask<Void, Void, Void>{
ArrayList<String> list;
protected void onPreExecute (){
super.onPreExecute();
list = new ArrayList<>();
}
protected Void doInBackground(Void...params){
InputStream is=null;
String result ="";
try {
HttpClient httpClient = new DefaultHttpClient();
HttpPost httpPost = new HttpPost("http://livetipsdotnet.000webhostapp.com/fetchspinner1.php");
HttpResponse response = httpClient.execute(httpPost);
HttpEntity entity = response.getEntity();
is = entity.getContent();
}
catch (IOException e){
e.printStackTrace();
}
try {
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(is,"UTF-8"));
String line="";
while ((line=bufferedReader.readLine())!=null)
{
result +=line;
}
is.close();
}
catch (IOException e){
e.printStackTrace();
}
try {
JSONArray jsonArray = new JSONArray(result);
for (int i=0; i<jsonArray.length(); i++)
{
JSONObject jsonObject = jsonArray.getJSONObject(i);
list.add(jsonObject.getString("id"));
}
}catch (JSONException e){
e.printStackTrace();
}
return null;
}
protected void onPostExecute (Void result){
listitems1.addAll(list);
adapter1.notifyDataSetChanged();
progressbar.setVisibility(View.GONE);
}
}//end of first spinner class
private class backTask2 extends AsyncTask<Void, Void, Void>{
ArrayList<String> list;
protected void onPreExecute (){
super.onPreExecute();
list = new ArrayList<>();
}
protected Void doInBackground(Void...params){
InputStream is=null;
String result ="";
try {
HttpClient httpClient = new DefaultHttpClient();
HttpPost httpPost = new HttpPost("http://livetipsdotnet.000webhostapp.com/fetchspinner2.php");
HttpResponse response = httpClient.execute(httpPost);
HttpEntity entity = response.getEntity();
is = entity.getContent();
}
catch (IOException e){
e.printStackTrace();
}
try {
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(is,"UTF-8"));
String line="";
while ((line=bufferedReader.readLine())!=null)
{
result +=line;
}
is.close();
}
catch (IOException e){
e.printStackTrace();
}
try {
JSONArray jsonArray = new JSONArray(result);
for (int i=0; i<jsonArray.length(); i++)
{
JSONObject jsonObject = jsonArray.getJSONObject(i);
list.add(jsonObject.getString("name"));
}
}catch (JSONException e){
e.printStackTrace();
}
return null;
}
protected void onPostExecute (Void result){
listitems2.addAll(list);
adapter2.notifyDataSetChanged();
progressbar.setVisibility(View.GONE);
}
}
public class LocationUpdateClass extends AsyncTask<String,Void,String> {
@Override
protected String doInBackground(String... params) {
String busID = params[0];
String busLoc = params[1];
String link = "http://livetipsdotnet.000webhostapp.com/buslocationupdt.php?busID="
+ busID + "&busLoc=" + busLoc;
try {
OkHttpClient client = new OkHttpClient();
RequestBody postData = new FormBody.Builder()
.add("type", "json")
.build();
Request request = new Request.Builder()
.url(link)
.post(postData)
.build();
Response response = client.newCall(request).execute();
String result = response.body().string();
return result;
} catch (Exception e) {
return e.getMessage().toString();
}
}
@Override
protected void onPostExecute(String getResult) {
super.onPostExecute(getResult);
DriversLocationUpdate.this.logstatus = getResult;
vtxtValidation.setText(getResult);
}
}
@Override
public void onItemSelected(AdapterView<?> parent, View selectedItemView, int position, long id) {
switch (parent.getId()){
case R.id.bus_arrays:
String list1 = parent.getItemAtPosition(position).toString();
res1.setText(list1);
Toast.makeText(parent.getContext(), "OnItemSelectedListener : " + list1, Toast.LENGTH_SHORT).show();
break;
case R.id.location_arrays:
String list2 = parent.getItemAtPosition(position).toString();
res2.setText(list2);
Toast.makeText(parent.getContext(), "OnItemSelectedListener : " + list2, Toast.LENGTH_SHORT).show();
break;
}
}
@Override
public void onNothingSelected(AdapterView<?> arg0) {
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.menu_drivers_location_update, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
return id == R.id.action_settings || super.onOptionsItemSelected(item);
}
}
E / AndroidRuntime：致命异常：主要 过程：tosan.example.tosan.buslocation，PID：11451 java.lang.NullPointerException：尝试调用虚方法＆＃39; void android.widget.TextView.setText（java.lang.CharSequence）＆＃39;在null对象引用上 at tosan.example.tosan.buslocation.DriversLocationUpdate $ LocationUpdateClass.onPostExecute（DriversLocationUpdate.java:224） at tosan.example.tosan.buslocation.DriversLocationUpdate $ LocationUpdateClass.onPostExecute（DriversLocationUpdate.java:196） 在android.os.AsyncTask.finish（AsyncTask.java:660） 在android.os.AsyncTask.-wrap1（AsyncTask.java） 在android.os.AsyncTask $ InternalHandler.handleMessage（AsyncTask.java:677） 在android.os.Handler.dispatchMessage（Handler.java:102） 在android.os.Looper.loop（Looper.java:154） 在android.app.ActivityThread.main（ActivityThread.java:6682） at java.lang.reflect.Method.invoke（Native Method） 在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:1520） 在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:1410）
答案 0 :(得分：0)
试试这个..
final Spinner spinner = (Spinner)findViewById(R.id.spinner);
spinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
@Override
public void onItemSelected(AdapterView<?> arg0, View arg1, int arg2, long arg3) {
String items = spinner.getSelectedItem().toString();
//Here give a network call
}
@Override
public void onNothingSelected(AdapterView<?> arg0) {
}
});