Question

由于我是Android的新手，我无法弄清楚为什么ListView不从ArrayList获取值，因此显示NullPointerException。

我正在尝试使用自定义对话框从TextView点击的json链接查看ListView中的内容。

logcat的：

02-26 05:42:22.905: E/AndroidRuntime(1441): FATAL EXCEPTION: main
02-26 05:42:22.905: E/AndroidRuntime(1441): java.lang.NullPointerException
02-26 05:42:22.905: E/AndroidRuntime(1441):     at com.example.customalertdialoglistview.MainActivity$1.onClick(MainActivity.java:106)
02-26 05:42:22.905: E/AndroidRuntime(1441):     at android.view.View.performClick(View.java:4204)
02-26 05:42:22.905: E/AndroidRuntime(1441):     at android.view.View$PerformClick.run(View.java:17355)
02-26 05:42:22.905: E/AndroidRuntime(1441):     at android.os.Handler.handleCallback(Handler.java:725)
02-26 05:42:22.905: E/AndroidRuntime(1441):     at android.os.Handler.dispatchMessage(Handler.java:92)
02-26 05:42:22.905: E/AndroidRuntime(1441):     at android.os.Looper.loop(Looper.java:137)
02-26 05:42:22.905: E/AndroidRuntime(1441):     at android.app.ActivityThread.main(ActivityThread.java:5041)
02-26 05:42:22.905: E/AndroidRuntime(1441):     at java.lang.reflect.Method.invokeNative(Native Method)
02-26 05:42:22.905: E/AndroidRuntime(1441):     at java.lang.reflect.Method.invoke(Method.java:511)
02-26 05:42:22.905: E/AndroidRuntime(1441):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
02-26 05:42:22.905: E/AndroidRuntime(1441):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
02-26 05:42:22.905: E/AndroidRuntime(1441):     at dalvik.system.NativeStart.main(Native Method)

MainActivity：

public void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    vehino = (TextView) findViewById(R.id.textView1);

    // add button listener
    vehino.setOnClickListener(new OnClickListener() {



        @TargetApi(Build.VERSION_CODES.GINGERBREAD)
        @Override
        public void onClick(View arg0) {

            // custom dialog
            final Dialog dialog = new Dialog(context);
            dialog.setContentView(R.layout.custom);
            dialog.setTitle("Select Id...");
            ThreadPolicy tp = ThreadPolicy.LAX;
            StrictMode.setThreadPolicy(tp);
            JSONParser jParser = new JSONParser();


            ArrayList<HashMap<String,String>> state_cons=new ArrayList<HashMap<String,String>>();

            try {
                json2=JSONfunctions
                        .getJSONfromURL("http://192.168.1.63/inba/mtc/mtc_enduser/vehicle_id_pop.php");
                jsonarray = json2.getJSONArray("vehicle");

                // looping through All Contacts
                for (int i=0;i<jsonarray.length();i++){
                    JSONObject c=jsonarray.getJSONObject(i);

                    HashMap<String,String> valuePairs=new HashMap<String,String>();

                    valuePairs.put("vehicle_id",c.getString(TAG_id));
                    valuePairs.put("vehicle_no", c.getString(TAG_no));
                    String state1 = c.getString(TAG_id);
                    String state2 = c.getString(TAG_no);
                    Log.d("states",state1 + state2);
                    state_cons.add(valuePairs);
                    state_cons.addAll(state_cons);

                    shippingid=state1;
                    cids=state2;

                    listview = (ListView) findViewById(R.id.listView1);

                    adapter = new ListViewAdapter(MainActivity.this, arraylist);

                    listview.setAdapter(adapter);
                }

                // set the custom dialog components - text, image and button
                dialog.show();

            }catch(JSONException e){
                e.printStackTrace();
            }
        }

        });}}

ListViewAdapter类：

public class ListViewAdapter extends BaseAdapter {

Context context;
LayoutInflater inflater;
ArrayList<HashMap<String, String>> data;

HashMap<String, String> resultp = new HashMap<String, String>();

public ListViewAdapter(Context context,
        ArrayList<HashMap<String, String>> arraylist) {
    this.context = context;
    data = arraylist;

}

@Override
public int getCount() {
    return data.size();

}

@Override
public Object getItem(int position) {
    return null;
}

@Override
public long getItemId(int position) {
    return 0;
}

@Override
public View getView(final int position, View convertView, ViewGroup parent) {

    TextView vehicle_id;
    TextView vehicle_no;

    View v = convertView;

    if (v == null) {
        LayoutInflater inflater = (LayoutInflater) context
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        v = inflater.inflate(R.layout.listview_item, null);
    }

    /*inflater = (LayoutInflater) context
            .getSystemService(Context.LAYOUT_INFLATER_SERVICE);*/

    /*View itemView = inflater.inflate(R.layout.listview_item, parent, false);*/

    resultp = data.get(position);

    vehicle_id = (TextView) v.findViewById(R.id.vid);
    Log.d("vehicle_id", "name" + vehicle_id);
    vehicle_no = (TextView) v.findViewById(R.id.vno);
    Log.d("vehicle_no", "name" + vehicle_no);

    vehicle_id.setText(resultp.get(MainActivity.TAG_id));
    vehicle_no.setText(resultp.get(MainActivity.TAG_no));

    v.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View arg0) {

            resultp = data.get(position);

            /*
             * intent.putExtra("name", resultp.get(Update.NAME));
             * intent.putExtra("age", resultp.get(Update.AGE));
             * 
             * 
             * context.startActivity(intent);
             */

        }

    });
    return v;
}}

谢谢。

Answer 1

adapter = new ListViewAdapter(MainActivity.this, arraylist);

需要指定“arrayList”，如果将其声明为变量，则为空

Answer 2

adapter = new ListViewAdapter(MainActivity.this, arraylist);

我认为arraylist值是Null .....

Answer 3

我发现你可能正在主线程上运行网络相关的操作，这是不可能的。

为此目的，您应该使用Thread或AsyncTask。

这部分必须在后台线程中

json2=JSONfunctions.getJSONfromURL("http://192.168.1.63/inba/mtc/mtc_enduser/vehicle_id_pop.php");

如果您说第106行是listview.setAdapter(adapter);，则listview为空。检查oyu是否在listView1

中包含ID为activity_main.xml的列表视图

列表视图中的java.lang.NullPointerException

3 个答案: