android - MainActivity找不到id为android.R.id.list的ListView，但是它是存在的

Question

我正在关注 this tutorial .

我已经根据我的应用程序的需要对其进行了修改，例如没有CRUD 功能和没有主菜单 - 我只想列出应用程序启动时执行的主要 Activity 期间的所有项目.

代码似乎没有错误，但运行它给我:Unfortunately, MyFirstApp has stopped in the VM.

LogCat 给我这个:

E/AndroidRuntime(910): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.myfirstproject/com.example.myfirstproject.MainActivity}: java.lang.RuntimeException: Your content must have a ListView whose id attribute is 'android.R.id.list'

做什么？我检查了我的 .xml 布局并进行了更改，但应用程序仍然崩溃。

MainActivity.java

package com.example.myfirstproject;

//imports

public class MainActivity extends ListActivity implements OnItemClickListener {

    // Progress Dialog
    private ProgressDialog pDialog;

    // Creating JSON Parser object
    JSONParser jParser = new JSONParser();

    ArrayList<HashMap<String, String>> carsList;

    // url to get all products list
    private static String url_all_cars = "http://localhost/webservice/get_all_cars.php";

    // JSON Node names
    private static final String TAG_SUCCESS = "success";
    private static final String TAG_CARS = "cars";
    private static final String TAG_NAME = "name";

    // products JSONArray
    JSONArray cars = null;

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

        // Hashmap for ListView
        carsList = new ArrayList<HashMap<String, String>>();

        // Loading products in Background Thread
        new LoadAllcars().execute();

        // Get listview
        ListView lv = getListView();
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.activity_main, menu);
        return true;
    }

    /**
     * Background Async Task to Load all product by making HTTP Request
     * */
    class LoadAllcars extends AsyncTask<String, String, String> {

        /**
         * Before starting background thread Show Progress Dialog
         * */
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            pDialog = new ProgressDialog(MainActivity.this);
            pDialog.setMessage("Loading cars. Please wait...");
            pDialog.setIndeterminate(false);
            pDialog.setCancelable(false);
            pDialog.show();
        }

        /**
         * getting All products from url
         * */
        protected String doInBackground(String... args) {
            // Building Parameters
            List<NameValuePair> params = new ArrayList<NameValuePair>();
            // getting JSON string from URL
            JSONObject json = jParser.makeHttpRequest(url_all_cars, "GET", params);

            // Check your log cat for JSON reponse
            Log.d("All cars: ", json.toString());

            try {
                // Checking for SUCCESS TAG
                int success = json.getInt(TAG_SUCCESS);

                if (success == 1) {
                    // products found
                    // Getting Array of Products
                    cars = json.getJSONArray(TAG_CARS);

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

                        // Storing each json item in variable
                        String title = c.getString(TAG_NAME);

                        // creating new HashMap
                        HashMap<String, String> map = new HashMap<String, String>();

                        // adding each child node to HashMap key => value
                        map.put(TAG_NAME, name);

                        // adding HashList to ArrayList
                        carsList.add(map);
                    }
                } else {
                    // no products found
                    pDialog = new ProgressDialog(MainActivity.this);
                    pDialog.setMessage("No cars found");
                    pDialog.setIndeterminate(false);
                    pDialog.setCancelable(false);
                    pDialog.show();
                }
            } catch (JSONException e) {
                e.printStackTrace();
            }

            return null;
        }

        /**
         * After completing background task Dismiss the progress dialog
         * **/
        protected void onPostExecute(String file_url) {
            // dismiss the dialog after getting all products
            pDialog.dismiss();
            // updating UI from Background Thread
            runOnUiThread(new Runnable() {
                public void run() {
                    /**
                     * Updating parsed JSON data into ListView
                     * */
                    ListAdapter adapter = new SimpleAdapter(
                            MainActivity.this, carsList,
                            android.R.id.list, new String[] {TAG_NAME},
                            new int[] { R.id.title });
                    // updating listview
                    setListAdapter(adapter);
                }
            });

        }
    }
}

activity_main.xml(带有 ListView 的主 Activity 的布局):

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/main_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >
    <ListView
        android:id="@+id/list"
        android:layout_width="fill_parent"
        android:layout_height="0dp"
        android:layout_weight="1" >
    </ListView>   
</LinearLayout>

list_item.xml(单个列表项的布局):

<?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" >

    <!-- Name Label -->
    <TextView
        android:id="@+id/name"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:paddingTop="6dip"
        android:paddingLeft="6dip"
        android:textSize="17dip"
        android:textStyle="bold" />

</LinearLayout>

Answer 1

看看他们如何在 ListActivity 文档中定义布局 here

您的 ListView Id 是 android:id="@+id/list" 并且它需要是 android:id="@android:id/list">/p>

另外，你的 ListAdapter 会崩溃

ListAdapter adapter = new SimpleAdapter(
                            MainActivity.this, carsList,
                            android.R.id.list, new String[] {TAG_NAME},
                            new int[] { R.id.title });

您告诉适配器使用 android ListView 作为 Item View 。 您应该为此传递您的 list_item.xml ID 并使用正确的 TextView ID(名称)

例如:

ListAdapter adapter = new SimpleAdapter(
                                MainActivity.this, carsList,
                                R.layout.list_item, new String[] {TAG_NAME},
                                new int[] { R.id.name});