我已经在json的asynctask中分配了字符串值，但它在onclick函数中显示为null值。这是我的字符串变量声明
public class MainActivity extends AppCompatActivity implements AdapterView.OnItemSelectedListener {
String due,total;
这是我在json
的asynctask中指定的字符串值total
JSONObject jsonObject = new JSONObject(str);
JSONArray jsonArray = jsonObject.getJSONArray("result");
for(int i=0; i< jsonArray.length(); i++)
{
JSONObject jo = jsonArray.getJSONObject(i);
total = jo.getString("due");
在此类total中分配为＆＃34; name1＆＃34;并且还在println中显示结果为logcat。但是当我在onclicklistener函数中将此值赋给其他字符串变量时，其println结果显示为null
这是我的完整活动代码
public class MainActivity extends AppCompatActivity implements AdapterView.OnItemSelectedListener {
private Spinner sname;
private EditText txtamount;
private ArrayList<String> names;
private ArrayAdapter<String> sdap;
String amount,mem,due,total;
TableLayout tableLayout;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
names = new ArrayList<String>();
tableLayout = findViewById(R.id.tblLoan);
sname = findViewById(R.id.spnMem);
sname.setOnItemSelectedListener(this);
txtamount = findViewById(R.id.txtLonCr);
Getdata getdata = new Getdata();
getdata.execute();
sdap = new ArrayAdapter<>(MainActivity.this,android.R.layout.simple_spinner_item, names);
sdap.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
sname.setAdapter(sdap);
}
protected class Getdata extends AsyncTask<Void,Void,Void>
{
private String jsonurl;
private String str;
@Override
protected void onPreExecute()
{
jsonurl="http://10.0.2.2/dwnloandata.php";
}
@Override
protected Void doInBackground(Void... voids) {
try {
tableLayout.removeAllViews();
URL url = new URL(jsonurl);
HttpURLConnection httpURLConnection=(HttpURLConnection)url.openConnection();
httpURLConnection.setRequestMethod("GET");
InputStream inputStream = httpURLConnection.getInputStream();
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
String line;
StringBuilder json = new StringBuilder();
while ((line = bufferedReader.readLine())!= null)
{
json.append(line).append('\n');
str=json.toString();
}
if (str != null){
JSONObject jsonObject = new JSONObject(str);
JSONArray name = jsonObject.getJSONArray("result");
for (int i=0; i< name.length(); i++)
{
JSONObject jo= name.getJSONObject(i);
names.add(jo.getString("name"));
TableRow raw = new TableRow(MainActivity.this);
TableRow.LayoutParams lp = new TableRow.LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.MATCH_PARENT);
raw.setLayoutParams(lp);
raw.setId(i+1);
TextView nm = new TextView(MainActivity.this);
nm.setWidth(650);
nm.setHeight(250);
nm.setTextSize(20);
nm.setText(jo.getString("name"));
TextView amnt = new TextView(MainActivity.this);
amnt.setTextSize(20);
amnt.setWidth(600);
amnt.setHeight(250);
amnt.setTextAlignment(TEXT_ALIGNMENT_CENTER);
amnt.setText(jo.getString("due"));
tableLayout.addView(raw);
raw.addView(nm);
raw.addView(amnt);
}}
bufferedReader.close();
inputStream.close();
httpURLConnection.disconnect();
} catch (IOException | JSONException e) {
e.printStackTrace();
}
return null;
}
@Override
protected void onPostExecute(Void aVoid) {
super.onPostExecute(aVoid);
sdap.notifyDataSetChanged();
}
}
@Override
public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
String item = parent.getItemAtPosition(position).toString();
mem=item;
}
@Override
public void onNothingSelected(AdapterView<?> parent) {
}
private class MembersLoan extends AsyncTask<String,Void,String> {
private String jsonurl,str;
@Override
protected void onPreExecute()
{
jsonurl = "http://10.0.2.2/dwnsingleloandata.php";
}
@Override
protected String doInBackground(String... strings) {
String member = strings[0];
try {
URL url = new URL(jsonurl);
HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
httpURLConnection.setRequestMethod("POST");
OutputStream outputStream = httpURLConnection.getOutputStream();
BufferedWriter bufferedWriter = new BufferedWriter(new OutputStreamWriter(outputStream,"UTF-8"));
String post_data = URLEncoder.encode("name","UTF-8") + "=" + URLEncoder.encode(member,"UTF-8");
bufferedWriter.write(post_data);
bufferedWriter.flush();
bufferedWriter.close();
InputStream inputStream = httpURLConnection.getInputStream();
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream,"iso-8859-1"));
String line;
StringBuilder jaon = new StringBuilder();
while ((line = bufferedReader.readLine()) != null)
{
jaon.append(line).append("\n");
str = jaon.toString();
}
if( str != null)
{
JSONObject jsonObject = new JSONObject(str);
JSONArray jsonArray = jsonObject.getJSONArray("result");
for(int i=0; i< jsonArray.length(); i++)
{
JSONObject jo = jsonArray.getJSONObject(i);
total = jo.getString("due");
System.out.println("due==" + total);
}
bufferedReader.close();
inputStream.close();
httpURLConnection.disconnect();
}
} catch (JSONException | IOException e) {
e.printStackTrace();
}
return null;
}
}
public void onClick(View view) {
amount = txtamount.getText().toString();
due = total;
LoanCreditInsert loanCreditInsert = new LoanCreditInsert(view.getContext());
loanCreditInsert.execute(mem,amount);
MembersLoan membersLoan = new MembersLoan();
membersLoan.execute(mem);
System.out.println("Amount=" + amount);
System.out.println("due=" + due);
int bdue = Integer.valueOf(due);
int ade = Integer.valueOf(amount);
int ldue = bdue - ade;
String ldu = String.valueOf(ldue);
LoanInsert loanInsert = new LoanInsert(view.getContext());
loanInsert.execute(mem,amount,ldu);
Getdata getdata = new Getdata();
getdata.execute();
}
}
答案 0 :(得分：0)
membersLoan.execute（MEM）;
在这样的调用之后，你不能拥有代码（使用doInBackground（）的结果）。
将以下所有代码放在MenbersLoan的onPostExecute中。
一般情况下：如果使用.execute（）启动asynctask，则调用后无法获得更多代码。如果您有“以下代码”，则将该代码放入该任务的onPostExecute（）中。
由于你有大约四个/五个asynctasks，你只能在前者的onPostExecute中调用下一个。
有工作要做......只需稍加编辑。
答案 1 :(得分：0)
LoanCreditInsert loanCreditInsert = new LoanCreditInsert(view.getContext());
loanCreditInsert.execute(mem,amount);
MembersLoan membersLoan = new MembersLoan();
membersLoan.execute(mem);
请逐个执行asynctask并尝试。