Question

我正在尝试搜索从URL获取的JSON数据，但只要用户键入搜索字符串，应用程序就会崩溃。我该如何解决？

这是我的代码：

MainActivity.java

public class MainActivity extends AppCompatActivity {

    private String TAG = MainActivity.class.getSimpleName();

    private ProgressDialog pDialog;
    private ListView lv;

    private EditText filterText;

    private ArrayAdapter<String> listAdapter;

    // URL to get contacts JSON
    private static String url = "http://210.213.86.195:14344/inventory/getallitemname";

    ArrayList<HashMap<String, String>> itemList;

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

        filterText = (EditText)findViewById(R.id.editText);

        itemList = new ArrayList<>();

        lv = (ListView) findViewById(R.id.list_item);

        new GetItems().execute();

        filterText.addTextChangedListener(new TextWatcher() {
            @Override
            public void beforeTextChanged(CharSequence s, int start, int count, int after) {

            }

            @Override
            public void onTextChanged(CharSequence s, int start, int before, int count) {
                MainActivity.this.listAdapter.getFilter().filter(s);
            }

            @Override
            public void afterTextChanged(Editable s) {

            }

        }
        );
    }

    /**
     * Async task class to get json by making HTTP call
     */
    private class GetItems extends AsyncTask<Void, Void, Void> {
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            // Showing progress dialog
            pDialog = new ProgressDialog(MainActivity.this);
            pDialog.setMessage("Please wait...");
            pDialog.setCancelable(false);
            pDialog.show();

        }

        @Override
        protected Void doInBackground(Void... arg0) {
            HttpHandler sh = new HttpHandler();

            // Making a request to url and getting response
            String jsonStr = sh.makeServiceCall(url);

            Log.e(TAG, "Response from url: " + jsonStr);

            if (jsonStr != null) {
                try {
                    JSONObject jsonObj = new JSONObject(jsonStr);

                    // Getting JSON Array node
                    JSONArray items = jsonObj.getJSONArray("Data");

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

                        String ItemCode = c.getString("ItemCode");
                        String ItemName = c.getString("ItemName");

                        // tmp hash map for single item
                        HashMap<String, String> item = new HashMap<>();

                        // adding each child node to HashMap key => value
                        item.put("ItemCode", ItemCode);
                        item.put("ItemName", ItemName);

                        // adding item to item list
                        itemList.add(item);
                    }

                } catch (final JSONException e) {
                    Log.e(TAG, "Json parsing error: " + e.getMessage());
                    runOnUiThread(new Runnable() {
                        @Override
                        public void run() {
                            Toast.makeText(getApplicationContext(),
                                    "Json parsing error: " + e.getMessage(),
                                    Toast.LENGTH_LONG)
                                    .show();
                        }
                    });

                }
            } else {
                Log.e(TAG, "Couldn't get json from server.");
                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        Toast.makeText(getApplicationContext(),
                                "Couldn't get json from server. Check LogCat for possible errors!",
                                Toast.LENGTH_LONG)
                                .show();
                    }
                });

            }

            return null;
        }

        @Override
        protected void onPostExecute(Void result) {
            super.onPostExecute(result);
            // Dismiss the progress dialog
            if (pDialog.isShowing())
                pDialog.dismiss();
            /**
             * Updating parsed JSON data into ListView
             * */
            ListAdapter adapter = new SimpleAdapter(
                    MainActivity.this, itemList,
                    R.layout.list_item, new String[]{"ItemCode", "ItemName"}, new int[]{R.id.ItemCode,
                    R.id.ItemName});

            lv.setAdapter(adapter);
        }

    }

}

activity_main.xml中

<?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"
    tools:context="com.example.jsonparser.MainActivity">

    <EditText
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/editText"
        android:layout_marginLeft="10dp"
        android:layout_marginRight="10dp"
        android:layout_alignParentTop="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true" />

    <ListView
        android:id="@+id/list_item"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginRight="5dp"
        android:layout_marginTop="10dp"
        android:layout_below="@+id/editText"
        android:layout_alignLeft="@+id/editText"
        android:layout_alignStart="@+id/editText" />
</RelativeLayout>

list_item.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical"
    android:padding="@dimen/activity_horizontal_margin">

    <TextView
        android:id="@+id/ItemName"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:paddingBottom="2dip"
        android:paddingTop="6dip"
        android:textColor="@color/colorPrimaryDark"
        android:textSize="16sp"
        android:textStyle="bold" />

    <TextView
        android:id="@+id/ItemCode"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:paddingBottom="2dip"
        android:textColor="@color/colorAccent" />
</LinearLayout>

Answer 1

你还没有把它放在代码的任何地方： -

MainActivity.this.listAdapter

所以默认为null，在postExecute中你正在使用本地适配器变量。

Answer 2

放

 adapter = new ArrayAdapter<String>(this,
                    R.layout.list_view_rows, R.id.listview, ListofStringYouWantToDisplay);

下面

lv = (ListView) findViewById(R.id.list_item);

听到 - ListofStringYouWantToDisplay是你要显示的String []或ArrayList

您的问题是您在使用前未初始化适配器

使用ListView

2 个答案: