Question

我知道这个答案已在某些页面上被提及并回答过，例如这个页面。 Android App crashes after Scrolling down ListView

但我尝试了答案，我的应用程序仍会崩溃，并给我一个空指针异常，我似乎无法找到我应该把if语句放在哪里或者如果我需要做一些完全不同的事情我的代码

package com.evanarendssgmail.php;

import android.app.AlertDialog;
import android.app.ListActivity;
import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.EditText;

import com.android.volley.RequestQueue;
import com.android.volley.Response;
import com.android.volley.toolbox.Volley;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

public class MainActivity extends ListActivity {


    private EditText name;
    private EditText buzz;
    private String [] names;
    private JSONObject jsonResponse;
    private String [] newNames;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        String [] evan = new String[10];
        for (int i = 0; i < 10; i ++) {
            evan[i] = "evan";
        }
        jsonResponse = null;

        Response.Listener<String> responseListener = new Response.Listener<String>() {
            @Override
            public void onResponse(String response) {
                String TAG = "YOUR TAG";
                Log.d(TAG,"after onResponse");
                try {

                    Log.d(TAG,"after try");
                    jsonResponse = new JSONObject(response);
                    Log.d(TAG,"after object initialization");
                    boolean success = jsonResponse.getBoolean("success");
                    Log.d(TAG,"after boolean statement");
                    if (success) {
                        Log.d(TAG,"Sucess");
                        //jarray = jsonResponse.getJSONArray("name");
                        if (jsonResponse != null) {
                            String lengt = Integer.toString(jsonResponse.length());
                            Log.d(TAG, "after lengt intialization");
                            int length = Integer.parseInt(lengt);
                            Log.d(TAG, "After length initialization");
                            names = new String[length];
                            Log.d(TAG, "after array initialization");
                            String number = "";
                            for (int i = 0; i < length - 1; i++) {
                                Log.d(TAG, "beginning loop");
                                number = Integer.toString(i);
                                Log.d(TAG, "mid loop");
                                names[i] = jsonResponse.getString(number);
                                Log.d(TAG, "End loop");
                            }
                        }
                        Log.d(TAG,"Before array adapter");
                        Log.d(TAG,"End of Tag");


                    } else {
                        AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this);
                        builder.setMessage("Login Failed")
                                .setNegativeButton("Retry", null)
                                .create()
                                .show();
                    }

                } catch (JSONException e) {
                    Log.d(TAG,"catch");
                    e.printStackTrace();
                }
            }
        };

        LoginRequest loginRequest = new LoginRequest(responseListener);
        RequestQueue queue = Volley.newRequestQueue(MainActivity.this);
        queue.add(loginRequest);

        //trnsfer();

        ArrayAdapter<String> adapter = new ArrayAdapter<String>(getListView().getContext(),android.R.layout.simple_list_item_1,names);
        getListView().setAdapter(adapter);




        name = (EditText) findViewById(R.id.name_text);
        buzz = (EditText) findViewById(R.id.buzz_text);
    }


    public void trnsfer() {

    }
    public void send_click(View v) {
        String nme = name.getText().toString();

        Response.Listener<String> responseListener = new Response.Listener<String>() {
            @Override
            public void onResponse(String response) {
                try {
                    JSONObject jsonResponse = new JSONObject(response);
                    boolean success = jsonResponse.getBoolean("success");
                    if (success) {
                        Intent intent = new Intent(MainActivity.this, MainActivity.class);
                        MainActivity.this.startActivity(intent);
                    } else {
                        AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this);
                        builder.setMessage("Register Failed")
                                .setNegativeButton("Retry", null)
                                .create()
                                .show();
                    }
                } catch (JSONException e) {
                    e.printStackTrace();
                }
            }
        };

        RegisterRequest registerRequest = new RegisterRequest(nme, responseListener);
        RequestQueue queue = Volley.newRequestQueue(MainActivity.this);
        queue.add(registerRequest);
    }

    public void reap() {
        Response.Listener<String> responseListener = new Response.Listener<String>() {
            @Override
            public void onResponse(String response) {
                String TAG = "YOUR TAG";
                Log.d(TAG,"after onResponse");
                try {
                    Log.d(TAG,"after try");
                    JSONObject jsonResponse = new JSONObject(response);
                    Log.d(TAG,"after object initialization");
                    boolean success = jsonResponse.getBoolean("success");
                    Log.d(TAG,"after boolean statement");
                    if (success) {
                        Log.d(TAG,"Sucess");
                        //jarray = jsonResponse.getJSONArray("name");
                        String lengt = Integer.toString(jsonResponse.length());
                        Log.d(TAG,"after lengt intialization");
                        int length = Integer.parseInt(lengt);
                        Log.d(TAG,"After length initialization");
                        names = new String[length];
                        Log.d(TAG,"after array initialization");
                        String number = "";
                        for (int i = 0; i < length - 1; i ++ ) {
                            Log.d(TAG,"beginning loop");
                            number = Integer.toString(i);
                            Log.d(TAG,"mid loop");
                            names[i] = jsonResponse.getString(number);
                            Log.d(TAG,"End loop");
                        }
                        Log.d(TAG,"Before array adapter");
                        Log.d(TAG,"End of Tag");


                    } else {
                        AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this);
                        builder.setMessage("Login Failed")
                                .setNegativeButton("Retry", null)
                                .create()
                                .show();
                    }

                } catch (JSONException e) {
                    Log.d(TAG,"catch");
                    e.printStackTrace();
                }
            }
        };

        LoginRequest loginRequest = new LoginRequest(responseListener);
        RequestQueue queue = Volley.newRequestQueue(MainActivity.this);
        queue.add(loginRequest);

    }
}

--- XML FILES

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.evanarendssgmail.php.MainActivity">


    <ListView
        android:layout_width="wrap_content"
        android:layout_height="250dp"
        android:id="@android:id/list"
        android:layout_below="@+id/buzz_text"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true" />

    <EditText
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/name_text"
        android:layout_alignParentTop="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:layout_alignRight="@android:id/list"
        android:layout_alignEnd="@android:id/list"
        android:text="Name" />

    <EditText
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/buzz_text"
        android:layout_below="@+id/name_text"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:layout_alignRight="@+id/name_text"
        android:layout_alignEnd="@+id/name_text"
        android:text="buzzword" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Send"
        android:id="@+id/button"
        android:onClick="send_click"
        android:layout_below="@android:id/list"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Receve"
        android:onClick="receve_click"
        android:id="@+id/button2"
        android:layout_below="@+id/button"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true" />
</RelativeLayout>

如果我将响应监听器放入onclick函数，它会将所有数据加载到listview中，但是一旦我滚动到底部，它将给我一个空指针异常。

滚动到底部

0 个答案: