OnItemClick给出空指针异常

Question

我已经设置了一个列表活动，一切都工作得很好，直到我想实现onitemclick()方法。我想在项目点击上启动一个新的活动，但它给空指针异常。我已经在舱单上申报了我所有的活动。下面是由list组成的活动:

DBLib.java

package com.example.test;
import java.util.ArrayList;
import java.util.HashMap;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import android.app.ListActivity;
import android.app.ProgressDialog;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.text.Editable;
import android.text.TextWatcher;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.SimpleAdapter;
public class DBLib extends ListActivity {
    private ProgressDialog pDialog;
    private EditText inputSearch;
    SimpleAdapter adapter;

    private static final String READ_DB_URL ="http://crshaggy.byethost7.com/webservice/warehouse.php";
    private static final String TAG_TITLE = "title";
    private static final String TAG_POSTS = "posts";
    private JSONArray mComments = null;

    private ArrayList<HashMap<String, String>> mCommentList;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.dblib_list);
        //inputSearch = (EditText)findViewById(R.id.et_search);
        //setListAdapter(new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1));
}
        @Override
    protected void onResume() {
        // TODO Auto-generated method stub
        super.onResume();
        // loading the comments via AsyncTask
        new LoadComments().execute();
    }
    public void updateJSONdata() {
    mCommentList = new ArrayList<HashMap<String, String>>();
    JSONParser jParser = new JSONParser();
    JSONObject json = jParser.getJSONFromUrl(READ_DB_URL);
    try{
        mComments = json.getJSONArray(TAG_POSTS);
        for (int i = 0; i < mComments.length(); i++) {
            JSONObject c = mComments.getJSONObject(i);
            String title = c.getString(TAG_TITLE);
        HashMap<String, String> map = new HashMap<String, String>();

        map.put(TAG_TITLE, title);
        mCommentList.add(map);
    }
} catch (JSONException e) {
            e.printStackTrace();
        }
    }

     void updateList() {
        adapter = new SimpleAdapter(this, mCommentList, 
        R.layout.post, new String[] { TAG_TITLE}, 
        new int[] { R.id.title});
        setListAdapter(adapter);

                ListView lv = getListView();    
        lv.setOnItemClickListener(new OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view,
                    int position, long id) {
                Intent openPost = new Intent(DBLib.this, BookDetail.class);
                startActivity(openPost);
                    }
                });
            }
    public class LoadComments extends AsyncTask<Void, Void, Boolean>{
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            pDialog = new ProgressDialog(DBLib.this);
            pDialog.setMessage("Loading Warehouse...");
            pDialog.setIndeterminate(false);
            pDialog.setCancelable(true);
            pDialog.show();
        }
        @Override
        protected Boolean doInBackground(Void... arg0) {
            updateJSONdata();
            return null;
        }
        @Override
        protected void onPostExecute(Boolean result) {
            super.onPostExecute(result);
            pDialog.dismiss();
            updateList();
            inputSearch = (EditText) findViewById(R.id.et_search);
            inputSearch.addTextChangedListener(new TextWatcher() {
                @Override
                public void onTextChanged(CharSequence cs, int arg1, int arg2, int arg3) {
                    // When user changed the Text
                    DBLib.this.adapter.getFilter().filter(cs);   
                }
                @Override
                public void beforeTextChanged(CharSequence arg0, int arg1, int arg2,
                        int arg3) {
                    // TODO Auto-generated method stub
                }
                @Override
                public void afterTextChanged(Editable arg0) {
                    // TODO Auto-generated method stub                          
                }
            });

}
    }
}

这是错误日志

08-06 14:13:45.116: E/AndroidRuntime(1673): FATAL EXCEPTION: main
08-06 14:13:45.116: E/AndroidRuntime(1673): Process: com.example.test, PID: 1673
08-06 14:13:45.116: E/AndroidRuntime(1673): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.test/com.example.test.BookDetail}: java.lang.NullPointerException
08-06 14:13:45.116: E/AndroidRuntime(1673):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2121)
08-06 14:13:45.116: E/AndroidRuntime(1673):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
08-06 14:13:45.116: E/AndroidRuntime(1673):     at android.app.ActivityThread.access$800(ActivityThread.java:135)
08-06 14:13:45.116: E/AndroidRuntime(1673):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
08-06 14:13:45.116: E/AndroidRuntime(1673):     at android.os.Handler.dispatchMessage(Handler.java:102)
08-06 14:13:45.116: E/AndroidRuntime(1673):     at android.os.Looper.loop(Looper.java:136)
08-06 14:13:45.116: E/AndroidRuntime(1673):     at android.app.ActivityThread.main(ActivityThread.java:5017)
08-06 14:13:45.116: E/AndroidRuntime(1673):     at java.lang.reflect.Method.invokeNative(Native Method)
08-06 14:13:45.116: E/AndroidRuntime(1673):     at java.lang.reflect.Method.invoke(Method.java:515)
08-06 14:13:45.116: E/AndroidRuntime(1673):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
08-06 14:13:45.116: E/AndroidRuntime(1673):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
08-06 14:13:45.116: E/AndroidRuntime(1673):     at dalvik.system.NativeStart.main(Native Method)
08-06 14:13:45.116: E/AndroidRuntime(1673): Caused by: java.lang.NullPointerException
08-06 14:13:45.116: E/AndroidRuntime(1673):     at com.example.test.BookDetail.<init>(BookDetail.java:14)
08-06 14:13:45.116: E/AndroidRuntime(1673):     at java.lang.Class.newInstanceImpl(Native Method)
08-06 14:13:45.116: E/AndroidRuntime(1673):     at java.lang.Class.newInstance(Class.java:1208)
08-06 14:13:45.116: E/AndroidRuntime(1673):     at android.app.Instrumentation.newActivity(Instrumentation.java:1061)
08-06 14:13:45.116: E/AndroidRuntime(1673):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2112)
08-06 14:13:45.116: E/AndroidRuntime(1673):     ... 11 more

BookDetail.java

package com.example.test;
import android.app.Activity;
import android.os.Bundle;
public class BookDetail extends Activity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.book_detail);
    }

}

清单

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.test"
    android:versionCode="1"
    android:versionName="1.0" >
    <uses-sdk
        android:minSdkVersion="13"
        android:targetSdkVersion="19" />
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
    <uses-permission android:name="android.permission.INTERNET" />
    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/MyTheme" >
        <activity
            android:name=".JSONParser"
            android:label="@string/title_activity_jsonpaerser" >
        </activity>
        <activity
            android:name=".Login"
            android:label="@string/title_activity_login" >
            <intent-filter>
                <action android:name="android.intent.action.LOGIN" />
                <category android:name="android.intent.category.DEFAULT" />
            </intent-filter>
        </activity>
        <activity
            android:name=".Register"
            android:label="@string/title_activity_register" >
        </activity>
        <activity
            android:name=".StartingPoint"
            android:label="@string/title_activity_starting_point" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity
            android:name=".DBLib"
            android:label="@string/title_activity_dblib" >
            <intent-filter>
                <action android:name="android.intent.action.SEARCH" />
            </intent-filter>
            <meta-data
                android:name="android.app.searchable"
                android:resource="@xml/searchable" />
        </activity>
        <activity
            android:name=".Index"
            android:label="@string/title_activity_index" >
        </activity>
        <activity
            android:name=".BookDetail"
            android:label="@string/title_activity_book_detail">
            <intent-filter>
                <action android:name="android.intent.action.BOOKDETAIL" />
                <category android:name="android.intent.category.DEFAULT" />
            </intent-filter> 
        </activity>
    </application>
</manifest>

Answer 1

试试这个:

public void onItemClick(AdapterView<?> parent, View view, int position, long id)
{
    Intent intent = new Intent(getApplicationContext(), BookDetail.class);
    startActivity(intent);
}