java - ClassCastException : android. widget.TextView 无法转换为 android.widget.ListView

Question

我不确定为什么会出现此类强制转换异常。我做了好几次 [Project --> Clean]，还是没用。

有人请帮助我。

谢谢。

这是ScheduleFragment.java

 public class ScheduleFragment extends Fragment {

    public static final String PREFS_NAME="PreferencesValue";

    public ProgressDialog pDialog;

    private ListView myListView;

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

    ArrayList<HashMap<String, String>> subjectList;     

    // url to get all subjects list
    private static String url_all_subjects = "http://192.168.1.12/android_project/get_subjects.php";

    // JSON Node names
    private static final String TAG_SUCCESS = "success";
    private static final String TAG_STUDENT = "student";
    private static final String TAG_MATRIX_ID = "matrix_id";
    private static final String TAG_NAME = "name";

    // subject JSONArray
    JSONArray student = null;


public ScheduleFragment(){}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
    View rootView = inflater.inflate(R.layout.fragment_schedule, container, false);

    //Bring the value from login page
   TextView tvmatrix = (TextView)rootView.findViewById(R.id.textViewMatrix);        
   SharedPreferences settings = getActivity().getSharedPreferences(PREFS_NAME, 0);        
   tvmatrix.setText(settings.getString("matrix", "A13123"));
    //-------------------------------------------------------------------------


 //------------------------------------CREATING A LISTVIEW-----------------------

    // Loading subject in Background Thread
    new LoadAllSubject().execute();

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

    myListView = (ListView) rootView.findViewById(R.id.textViewMatrix);

    // on selecting single subject
    myListView.setOnItemClickListener(new OnItemClickListener() {

        @Override
        public void onItemClick(AdapterView<?> parent, View view,
                int position, long id) {
            // getting values from selected ListItem
            String matrix_id = ((TextView) view.findViewById(R.id.textViewMatrix)).getText()
                    .toString();

            // Starting new intent
            Intent in = new Intent(getActivity().getApplicationContext(),
                    SingleSubject.class);

            // sending matrix id to next activity
            in.putExtra(TAG_MATRIX_ID, matrix_id);

            // starting new activity and expecting some response back
            startActivityForResult(in, 100);
        }
    });

    return rootView;
}

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

    /**
     * Before starting background thread Show Progress Dialog
     * */

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        pDialog = ProgressDialog.show(ScheduleFragment.this.getActivity(), "Progress", "Loading subjects. Please wait...", false);
        pDialog.setIndeterminate(false);
        pDialog.setCancelable(false);
    }

    /**
     * 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_subjects, "GET", params);

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

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

            if (success == 1) {
                // subject found
                // Getting Array of Subject
                student = json.getJSONArray(TAG_STUDENT);

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

                    // Storing each json item in variable
                    String matrix_id = c.getString(TAG_MATRIX_ID);
                    String name = 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_MATRIX_ID, matrix_id);
                    map.put(TAG_NAME, name);

                    // adding HashList to ArrayList
                    subjectList.add(map);
                }
            } else {
                // no subjects found

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

        return null;
    }

    /**
     * After completing background task Dismiss the progress dialog
     * **/
    protected void onPostExecute(String file_url) {
        super.onPostExecute(file_url);
        // dismiss the dialog after getting all products
        pDialog.dismiss();
        // updating UI from Background Thread           
                 ListAdapter adapter = new SimpleAdapter(
                           getActivity(), subjectList,
                        R.layout.all_subject, new String[] { TAG_MATRIX_ID,
                                TAG_NAME},
                        new int[] { R.id.matrix_id, R.id.name });
                // updating listview
                myListView.setAdapter(adapter);
    }
}
 }

这是 all_subject.xml

     <TextView
    android:id="@+id/matrix_id"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:visibility="gone" />


<!-- 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" />

这是fragment_schedule.xml

        <ListView
    android:id="@android:id/list"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"/>

<TextView
    android:id="@+id/textViewMatrix"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentTop="true"
    android:layout_centerHorizontal="true"
    android:layout_marginTop="66dp"
    android:text="Large Text"
    android:textAppearance="?android:attr/textAppearanceLarge" />

这是错误日志。

    03-25 12:14:06.177: W/dalvikvm(1129): threadid=1: thread exiting with uncaught   exception (group=0x40d09930)
      03-25 12:14:06.271: E/AndroidRuntime(1129): FATAL EXCEPTION: main
      03-25 12:14:06.271: E/AndroidRuntime(1129): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.ultra.esc/com.ultra.esc.HomeActivity}: java.lang.ClassCastException: android.widget.TextView cannot be cast to android.widget.ListView
      03-25 12:14:06.271: E/AndroidRuntime(1129):   at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
     03-25 12:14:06.271: E/AndroidRuntime(1129):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
     03-25 12:14:06.271: E/AndroidRuntime(1129):    at android.app.ActivityThread.access$600(ActivityThread.java:141)
     03-25 12:14:06.271: E/AndroidRuntime(1129):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
     03-25 12:14:06.271: E/AndroidRuntime(1129):    at android.os.Handler.dispatchMessage(Handler.java:99)
     03-25 12:14:06.271: E/AndroidRuntime(1129):    at android.os.Looper.loop(Looper.java:137)
     03-25 12:14:06.271: E/AndroidRuntime(1129):    at android.app.ActivityThread.main(ActivityThread.java:5039)
     03-25 12:14:06.271: E/AndroidRuntime(1129):    at java.lang.reflect.Method.invokeNative(Native Method)
    03-25 12:14:06.271: E/AndroidRuntime(1129):     at java.lang.reflect.Method.invoke(Method.java:511)
     03-25 12:14:06.271: E/AndroidRuntime(1129):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
    03-25 12:14:06.271: E/AndroidRuntime(1129):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
    03-25 12:14:06.271: E/AndroidRuntime(1129):     at dalvik.system.NativeStart.main(Native Method)
    03-25 12:14:06.271: E/AndroidRuntime(1129): Caused by: java.lang.ClassCastException: android.widget.TextView cannot be cast to android.widget.ListView
    03-25 12:14:06.271: E/AndroidRuntime(1129):     at com.ultra.esc.ScheduleFragment.onCreateView(ScheduleFragment.java:88)
    03-25 12:14:06.271: E/AndroidRuntime(1129):     at android.app.Fragment.performCreateView(Fragment.java:1695)
    03-25 12:14:06.271: E/AndroidRuntime(1129):     at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:885)
    03-25 12:14:06.271: E/AndroidRuntime(1129):     at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1057)
    03-25 12:14:06.271: E/AndroidRuntime(1129):     at android.app.BackStackRecord.run(BackStackRecord.java:682)
    03-25 12:14:06.271: E/AndroidRuntime(1129):     at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1435)
    03-25 12:14:06.271: E/AndroidRuntime(1129):     at android.app.Activity.performStart(Activity.java:5113)
   03-25 12:14:06.271: E/AndroidRuntime(1129):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2153)
   03-25 12:14:06.271: E/AndroidRuntime(1129):  ... 11 more

Answer 1

这里你错了

 myListView = (ListView) rootView.findViewById(R.id.textViewMatrix);

textViewMatrix 是 TextView id 而不是 ListView id 并发布您的 fragment_schedule.xml 文件

然后改变这个

<ListView
  android:id="@android:id/list" ...../>

到

<ListView
    android:id="@+id/list"
    .......
    ......../>

并在您的 fragment 中使用

myListView = (ListView) rootView.findViewById(R.id.list);