Question

我创建了这个在doInBackground中无法正常工作的AsyncTask。为了更好地理解，我指出了一些事情：

getFunctionVal(String function, double Val);此方法返回以点计算的函数的值（例如：getFunctionVal("x+3", 2.0) = 5.0）。
funzione和derivata是两个字符串（它们是公式）。

问题：我无法理解为什么soluzioni.size()始终为0，risultati.size()也会发生同样的事情。当我在UI中的OnClickListener内部使用此代码时，这并没有发生。

  public double b = -20;
  public double a = -20;

  public class TaskAsincrono extends AsyncTask<Void, Void, Boolean> {

    private Context mContext;
    private View view;
    public List<Double> risultati = new ArrayList<>();
    public List<Double> soluzioni = new ArrayList<>();
    private ProgressDialog dialog;

    public TaskAsincrono (Context context, View v){
        mContext = context;
        view = v;
    }

    @Override
    protected void onPreExecute(){
      dialog = ProgressDialog.show(view.getContext(), "", "Attendi...", false, true);
    }

    @Override
    protected void onProgressUpdate(Void[] values) {

    };

    @Override
    protected Boolean doInBackground(Void... params) {

        int step = 500;
        double k = (b-a)/step;

        List<Double> valoriIntervallo = new ArrayList<>();
        List<Double> valoriFunzione = new ArrayList<>();

        //Generates number for intervals
        for(int i = 0; i < step; i++) {
            double ak = a + k;
            double fak = getFunctionVal(funzione, ak);
            a += k;
            valoriIntervallo.add(ak);
            valoriFunzione.add(fak);
        }

        //show the number intervals
        for(int j = 0; j < valoriIntervallo.size()-1; j++) {

            if (Math.signum(valoriFunzione.get(j)) != Math.signum(valoriFunzione.get(j+1))) {
                risultati.add(valoriIntervallo.get(j));
                risultati.add(valoriIntervallo.get(j+1));
            }

        }

            k = 0;

            for (int i = 0; i < (risultati.size()); i += 2) {

                k++;
                double a = risultati.get(i);
                double b = risultati.get(i + 1);
                double res = (b + a) / 2;

                for (int j = 1; j < 10; j++) {
                    res = res - (getFunctionVal(funzione, res) / getFunctionVal(derivata, res));
                }

                soluzioni.add(res);

            }

        return true;
    }

    @Override
    protected void onPostExecute(final Boolean success) {

        if(dialog.isShowing()) { dialog.dismiss(); }

        TableLayout tl = (TableLayout) view.findViewById(R.id.tableLayoutTangenti);

        for (int o = 0; o < 1; o++) {

            TableRow tr = new TableRow(mContext);
            tr.setLayoutParams(new TableRow.LayoutParams(TableRow.LayoutParams.MATCH_PARENT, TableRow.LayoutParams.WRAP_CONTENT));

            TextView coefficente = new TextView(mContext);
            coefficente.setText("x" + String.valueOf((o+1)) + " = ");
            coefficente.setGravity(Gravity.CENTER);
            coefficente.setLayoutParams(new TableRow.LayoutParams(0, TableRow.LayoutParams.WRAP_CONTENT, 0.2f));

            EditText decimale = new EditText(mContext);
            decimale.setGravity(Gravity.CENTER);
            decimale.setText(String.valueOf(risultati.size()));
            decimale.setFocusable(false);
            decimale.setFocusableInTouchMode(false);
            decimale.setClickable(false);
            decimale.setLayoutParams(new TableRow.LayoutParams(0, TableRow.LayoutParams.WRAP_CONTENT, 0.8f));

            tr.addView(coefficente);
            tr.addView(decimale);
            tl.addView(tr, new TableLayout.LayoutParams(TableLayout.LayoutParams.MATCH_PARENT, TableLayout.LayoutParams.WRAP_CONTENT));
        }
    }

    @Override
    protected void onCancelled() {
        mAuthTask = null;
    }
}

如果你问我为什么要使用AsyncTask，那是因为我需要step = 50000而我不能强调＃34;用户界面这么多。

Answer 1

检查条件 if（Math.signum（valoriFunzione.get（j））！= Math.signum（valoriFunzione.get（j + 1）））评估为真。

Answer 2

k为0. funzione是常量。假设getFunctionVal是纯函数，valoriFunzione包含相同值的500倍。

这意味着Math.signum(valoriFunzione.get(j)) != Math.signum(valoriFunzione.get(j+1))始终为假。

这就是risultati中没有任何内容的原因。

ArrayList在AsyncTask中不起作用

2 个答案: