Question

我已经声明了这个多维ArrayList：

public class Rete {

public RequestQueue requestQueue;
public ArrayList<ArrayList<String>> result = new ArrayList<ArrayList<String>>();


public Rete(RequestQueue requestQueue) {
    this.requestQueue = requestQueue;
    result.add(new ArrayList<String>(4));
}

}

我想要添加这样的数据：

for (int i = 0; i < utenti.length(); i++) {
                    JSONObject student = utenti.getJSONObject(i);

                    result.get(i).add(student.getString("nome"));
                    result.get(i).add(student.getString("cognome"));
                    result.get(i).add(student.getString("numero"));
                    result.get(i).add(student.getString("email"));

                }

但应用程序崩溃... logcat：

10-11 20:10:27.048    6429-6429/com.rete.prova.ale.reteale E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.rete.prova.ale.reteale, PID: 6429
java.lang.IndexOutOfBoundsException: Invalid index 1, size is 1
        at java.util.ArrayList.throwIndexOutOfBoundsException(ArrayList.java:255)
        at java.util.ArrayList.get(ArrayList.java:308)
        at com.rete.prova.ale.reteale.Rete$4.onResponse(Rete.java:101)
        at com.rete.prova.ale.reteale.Rete$4.onResponse(Rete.java:89)
        at com.android.volley.toolbox.JsonRequest.deliverResponse(JsonRequest.java:65)
        at com.android.volley.ExecutorDelivery$ResponseDeliveryRunnable.run(ExecutorDelivery.java:99)
        at android.os.Handler.handleCallback(Handler.java:739)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:148)
        at android.app.ActivityThread.main(ActivityThread.java:5417)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

问题是ArrayList ..如何以正确的方式对它们进行初始化？

Answer 1

这是你的arraylist

public ArrayList<ArrayList<String>> result = new ArrayList<ArrayList<String>>();

这就是你出错的地方

result.get(i).add(student.getString("nome"));
result.get(i).add(student.getString("cognome"));
result.get(i).add(student.getString("numero"));
result.get(i).add(student.getString("email"));

您正在获取 IndexOutOfBoundsException ，因为您正在尝试从空数组中获取对象。

试试这个

ArrayList<String> studentdata = new ArrayList<String>();
studentdata.add(student.getString("nome"));
studentdata.add(student.getString("cognome"));
studentdata.add(student.getString("numero"));
studentdata.add(student.getString("email"));

result.add(studentdata);

Answer 2

在for循环的每次迭代中，您需要实例化一个新的<root>并将其添加到ArrayList

result

并摆脱

for (int i = 0; i < utenti.length(); i++) {
        JSONObject student = utenti.getJSONObject(i);
        ArrayList<String> tmp = new ArrayList<>(4);
        tmp.add(student.getString("nome"));
        tmp.add(student.getString("cognome"));
        tmp.add(student.getString("numero"));
        tmp.add(student.getString("email"));
        result.add(tmp);
}

多维ArrayListy inizialize

2 个答案: