java.lang.RuntimeException : Unable to start activity ComponentInfo{. ..} : java. lang.NullPointerException

Question

似乎有很多问题与我的类似，但那里发布的答案似乎对我不起作用。我的程序应该只是打开一个允许 webview 的新页面。 但是当我尝试打开此页面时，会显示错误，但没有太多提示问题所在。

public class DetailedEventActivity extends Activity {

    TextView name;
    TextView desc;
    TextView link;

    String pid;
    String myName;
    String myDesc;
    String myLink;
    Button eLink;


    // Progress Dialog
    private ProgressDialog pDialog;

    // JSON parser class
    JSONParser jsonParser = new JSONParser();

    // single profile url
    private static final String url_event_detials = "http://10.0.2.2:8888/week_6/get_all_event.php";

    // JSON Node names
    private static final String TAG_SUCCESS = "success";
    private static final String TAG_EVENT = "event";
    private static final String TAG_PID = "eventID";
    private static final String TAG_NAME = "eventName";
    private static final String TAG_DESC = "eventDescription";
    private static final String TAG_LINK = "link";

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

        // getting profile details from intent
        Intent i = getIntent();

        // getting profile id (pid) from intent
        pid = i.getStringExtra(TAG_PID);
        myName = i.getStringExtra(TAG_NAME);
        myDesc = i.getStringExtra(TAG_DESC);
        myLink = i.getStringExtra(TAG_LINK);

        name = (TextView) findViewById(R.id.inputName);
        desc = (TextView) findViewById(R.id.inputDesc);
        //link = (TextView) findViewById(R.id.inputLink);

        name.setText(myName);
        desc.setText(myDesc);
        link.setText(myLink);

        eLink = (Button) findViewById(R.id.eventLink);

        eLink.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View view) {
                WebView webview = new WebView(DetailedEventActivity.this);
                setContentView(webview);
                WebSettings webSettings = webview.getSettings();
                webSettings.setJavaScriptEnabled(true);

                webview.loadUrl(myLink);
             }
        }); 



        // Getting complete profile details in background thread

    } 

这些代码通向另一个类。

public class ViewEventActivity extends ListActivity {

    String pid;
    String name;
    String desc;
    String link;

    // Progress Dialog
    private ProgressDialog pDialog;

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

    ArrayList<HashMap<String, String>> eventList;

    // url to get all profile list
    private static String url_all_event = "http://10.0.2.2:8888/week_6/get_all_event.php";

    // JSON Node names
    private static final String TAG_SUCCESS = "success";
    private static final String TAG_EVENT = "event";
    private static final String TAG_PID = "eventID";
    private static final String TAG_NAME = "eventName";
    private static final String TAG_DESC = "eventDescription";
    private static final String TAG_LINK = "link";

    // profiles JSONArray
    JSONArray event = null;

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

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

        // Loading profiles in Background Thread
        new LoadAllEvent().execute();

        // Get listview
        ListView lv = getListView();
        // on seleting single event
        // launching Edit event Screen

        lv.setOnItemClickListener(new OnItemClickListener() {

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

                //Roy
                String myPid = eventList.get(position).get(TAG_PID);
                String myName = eventList.get(position).get(TAG_NAME);
                String myDesc = eventList.get(position).get(TAG_DESC);
                String myLink = eventList.get(position).get(TAG_LINK);

                // Starting new intent
                Intent in = new Intent(getApplicationContext(),DetailedEventActivity.class);
                // sending pid to next activity
                in.putExtra(TAG_PID, myPid);
                Log.d("Put Extra ", "id = "+ myPid);
                in.putExtra(TAG_NAME, myName);
                Log.d("Put Extra ", "name = "+ myName);
                in.putExtra(TAG_DESC, myDesc);
                Log.d("Put Extra ", "desc = "+ myDesc);
                in.putExtra(TAG_LINK, myLink);
                Log.d("Put Extra ", "link = "+ myLink);
                // starting new activity and expecting some response back
               startActivityForResult(in, 100);
            }
        }); 

    }

    // Response from Edit profile Activity
    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        // if result code 100
        if (resultCode == 100) {
            // if result code 100 is received
            // means user edited/deleted profile
            // reload this screen again
            Intent intent = getIntent();
            finish();
            startActivity(intent);
        }

    }

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

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

        /**
         * getting All profiles 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_event, "GET", params);

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

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

                if (success == 1) {
                    // profiles found
                    // Getting Array of profiles
                    event = json.getJSONArray(TAG_EVENT);

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

                        Log.d("View Json ", "i = "+i);
                        // Storing each json item in variable
                        String id = c.getString(TAG_PID);
                        Log.d("View Json ", "id = "+ id);
                        String name = c.getString(TAG_NAME);
                        Log.d("View Json ", "name = "+ name);
                        String desc = c.getString(TAG_DESC);
                        Log.d("View Json ", "desc = "+ desc);
                        String link = c.getString(TAG_LINK);
                        Log.d("View Json ", "link = "+ link);

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

                        // adding each child node to HashMap key => value
                        map.put(TAG_PID, id);
                        map.put(TAG_NAME, name);
                        map.put(TAG_DESC, desc);
                        map.put(TAG_LINK, link);

                        // adding HashList to ArrayList
                        eventList.add(map);
                    }
                } else {
                    // no profiles found
                    // Launch Add New profile Activity
                    Intent i = new Intent(getApplicationContext(),
                            MainScreenActivity.class);
                    //Main Page Aagin
                    pDialog = new ProgressDialog(ViewEventActivity.this);
                    pDialog.setMessage("Redirecting to main page");
                    pDialog.setIndeterminate(false);
                    pDialog.setCancelable(false);
                    pDialog.show();
                    // Closing all previous activities
                    i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
                    startActivity(i);
                }
            } 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 profiles
            pDialog.dismiss();
            // updating UI from Background Thread
            runOnUiThread(new Runnable() {
                public void run() {
                    /**
                     * Updating parsed JSON data into ListView
                     * */
                    ListAdapter adapter = new SimpleAdapter(
                            ViewEventActivity.this, eventList,
                            R.layout.list_event, new String[] { TAG_PID,
                                    TAG_NAME},
                            new int[] { R.id.pid, R.id.name });
                    // updating listview
                    setListAdapter(adapter);
                }
            });

        }

    }
}

我在 LogCat 上不断遇到的错误是:

11-17 11:21:55.819: E/AndroidRuntime(1391): FATAL EXCEPTION: main
11-17 11:21:55.819: E/AndroidRuntime(1391): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.test/com.example.test.DetailedEventActivity}: java.lang.NullPointerException
11-17 11:21:55.819: E/AndroidRuntime(1391):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
11-17 11:21:55.819: E/AndroidRuntime(1391):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
11-17 11:21:55.819: E/AndroidRuntime(1391):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
11-17 11:21:55.819: E/AndroidRuntime(1391):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
11-17 11:21:55.819: E/AndroidRuntime(1391):     at android.os.Handler.dispatchMessage(Handler.java:99)
11-17 11:21:55.819: E/AndroidRuntime(1391):     at android.os.Looper.loop(Looper.java:137)
11-17 11:21:55.819: E/AndroidRuntime(1391):     at android.app.ActivityThread.main(ActivityThread.java:5103)
11-17 11:21:55.819: E/AndroidRuntime(1391):     at java.lang.reflect.Method.invokeNative(Native Method)
11-17 11:21:55.819: E/AndroidRuntime(1391):     at java.lang.reflect.Method.invoke(Method.java:525)
11-17 11:21:55.819: E/AndroidRuntime(1391):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
11-17 11:21:55.819: E/AndroidRuntime(1391):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
11-17 11:21:55.819: E/AndroidRuntime(1391):     at dalvik.system.NativeStart.main(Native Method)
11-17 11:21:55.819: E/AndroidRuntime(1391): Caused by: java.lang.NullPointerException
11-17 11:21:55.819: E/AndroidRuntime(1391):     at com.example.test.DetailedEventActivity.onCreate(DetailedEventActivity.java:77)
11-17 11:21:55.819: E/AndroidRuntime(1391):     at android.app.Activity.performCreate(Activity.java:5133)
11-17 11:21:55.819: E/AndroidRuntime(1391):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
11-17 11:21:55.819: E/AndroidRuntime(1391):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
11-17 11:21:55.819: E/AndroidRuntime(1391):     ... 11 more

我知道这个问题可能看起来微不足道，但我上个月才开始学习java，所以非常感谢指导和帮助。谢谢!

Answer 1

您在没有正确初始化的情况下访问链接对象:

  //link = (TextView) findViewById(R.id.inputLink);
  link.setText(myLink);