我从服务器获取json数据，我想将该数据传递给我的数据库，我想在我的listview中显示这些数据，现在它的一些空指针异常。
Mainactivity.java
public class MainActivity extends ListActivity implements FetchDataListener,OnClickListener{
private static final int ACTIVITY_CREATE=0;
private static final int TAG_CATEGORY = 0;
private static final String CATEGORY_COLUMN_ID = "_id";
private static final String CATEGORY_COLUMN_TITLE = "title";
private static final String CATEGORY_COLUMN_CONTENT = "content";
private static final String CATEGORY_COLUMN_COUNT = "count";
private static final int Application = 0;
private ProgressDialog dialog;
ListView lv;
ListView lv1;
private List<Application> items;
private Button btnGetSelected;
private Button praycount;
public int pct;
private String stringVal;
private TextView value;
private int prayers;
private int prayerid;
EditText myFilter;
ApplicationAdapter adapter;
private GinfyDbAdapter mDbHelper;
JSONArray contacts = null;
private SimpleCursorAdapter dataAdapter;
@Override
protected void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_list_item);
mDbHelper=new GinfyDbAdapter(MainActivity.this);
mDbHelper.open();
fillData();
registerForContextMenu(getListView());
lv1 =(ListView)findViewById(R.id.list);
lv =(ListView)findViewById(R.id.list);
btnGetSelected = (Button) findViewById(R.id.btnget);
btnGetSelected.setOnClickListener(this);
myFilter = (EditText) findViewById(R.id.myFilter);
// Adding items to listview
/**
* Enabling Search Filter
* */
new GetDataAsyncTask().execute();
//praycount.setOnClickListener(this);
//initView();
}
/*private void initView(){
// show progress dialog
dialog = ProgressDialog.show(this, "", "Loading...");
String url = "http://www.ginfy.com/api/v1/posts.json";
FetchDataTask task = new FetchDataTask(this);
task.execute(url);
} */
private class GetDataAsyncTask extends AsyncTask<Void, Void, Boolean> {
private ProgressDialog Dialog = new ProgressDialog(MainActivity.this);
protected void onPreExecute() {
Dialog.setMessage("Loading.....");
Dialog.show();
}
@Override
protected void onPostExecute(Boolean result) {
super.onPostExecute(result);
Dialog.dismiss();
Intent intent = new Intent(MainActivity.this, MainActivity.class);
startActivity(intent);
}
@Override
protected Boolean doInBackground(Void... params) {
getProdData();
return null;
}
}
public void getProdData() {
// getting JSON string from URL
JSONParser jsonObject = new JSONParser();
//JSONObject jsonObject = new JSONObject();
//JSONArray aJson = jsonObject.getJSONArray("post");
String url = "http://www.ginfy.com/api/v1/posts.json";
// getting JSON string from URL
//JSONArray aJson = jsonObject.getJSONArray(url);
JSONArray Json = jsonObject.getJSONFromUrl(url);
try {
// Getting Array of Contacts
contacts = Json.getJSONArray(TAG_CATEGORY);
// looping through All Contacts
for(int i = 0; i < contacts.length(); i++){
JSONObject c = contacts.getJSONObject(i);
// Storing each json item in variable
String id = c.getString(CATEGORY_COLUMN_ID);
String title = c.getString(CATEGORY_COLUMN_TITLE);
String content = c.getString(CATEGORY_COLUMN_CONTENT);
String count = c.getString(CATEGORY_COLUMN_COUNT);
mDbHelper.saveCategoryRecord(new Category(id,title,content,count));
}
} catch (JSONException e) {
e.printStackTrace();
}
}
@SuppressLint("NewApi")
@SuppressWarnings("deprecation")
private void fillData() {
mDbHelper.open();
Cursor projectsCursor = mDbHelper.fetchAllProjects();
//startManagingCursor(projectsCursor);
// Create an array to specify the fields we want to display in the list (only TITLE)
String[] from = new String[]{GinfyDbAdapter.CATEGORY_COLUMN_TITLE, GinfyDbAdapter.CATEGORY_COLUMN_CONTENT, GinfyDbAdapter.CATEGORY_COLUMN_COUNT};
// and an array of the fields we want to bind those fields to (in this case just text1)
int[] to = new int[]{R.id.text2, R.id.text1, R.id.count};
/* Now create a simple cursor adapter and set it to display
SimpleCursorAdapter projects =
new SimpleCursorAdapter(this, R.layout.activity_row, projectsCursor, from, to);
setListAdapter(projects);
*/
// create the adapter using the cursor pointing to the desired data
//as well as the layout information
dataAdapter = new SimpleCursorAdapter(
this, R.layout.activity_row,
projectsCursor,
from,
to,
0);
setListAdapter(dataAdapter);
}
private void setListAdapter(SimpleCursorAdapter dataAdapter2) {
// TODO Auto-generated method stub
}
它显示此行registerForContextMenu(getListView());中的错误，它会引发空指针异常。
mycategory.java
public class Category {
String _id;
String title;
String content;
String count;
public Category(String id, String title, String content, String count) {
super();
this._id = id;
this.title = title;
this.content = content;
this.count = count;
}
public String getId() {
return _id;
}
public void setId(String id) {
this._id = id;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
public String getContent() {
return content;
}
public void setContent(String content) {
this.content = content;
}
public String getCount() {
return count;
}
public void setCount(String count) {
this.count = count;
}
}
这是我的db部分，我正在给予
public class GinfyDbAdapter {
private static final String DATABASE_NAME = "test";
private static final String DATABASE_TABLE_PROJ = "projects";
private static final int DATABASE_VERSION = 3;
public static final String CATEGORY_COLUMN_ID = "_id";
public static final String CATEGORY_COLUMN_TITLE = "title";
public static final String CATEGORY_COLUMN_CONTENT = "content";
public static final String CATEGORY_COLUMN_COUNT = "count";
private static final String TAG = "GinfyDbAdapter";
private DatabaseHelper mDbHelper;
private static SQLiteDatabase mDb;
private final Context mCtx;
public void saveCategoryRecord(String id, String title, String content, String count) {
ContentValues contentValues = new ContentValues();
contentValues.put(CATEGORY_COLUMN_ID, id);
contentValues.put(CATEGORY_COLUMN_TITLE, title);
contentValues.put(CATEGORY_COLUMN_CONTENT, content);
contentValues.put(CATEGORY_COLUMN_COUNT, count);
mDb.insert(DATABASE_NAME, null, contentValues);
}
public Cursor getTimeRecordList() {
return mDb.rawQuery("select * from " + DATABASE_NAME, null);
}
private static class DatabaseHelper extends SQLiteOpenHelper {
DatabaseHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
private static final String DATABASE_CREATE_PROJ =
"create table " + DATABASE_TABLE_PROJ + " ("
+ CATEGORY_COLUMN_ID + " integer primary key , "
+ CATEGORY_COLUMN_TITLE + " text not null, " + CATEGORY_COLUMN_CONTENT + " text not null, " + CATEGORY_COLUMN_COUNT + " integer );" ;
@Override
public void onCreate(SQLiteDatabase db) {
// TODO Auto-generated method stub
String DATABASE_CREATE_PROJ = "CREATE TABLE " + DATABASE_TABLE_PROJ + "( "
+ CATEGORY_COLUMN_ID + " INTEGER PRIMARY KEY, "
+ CATEGORY_COLUMN_TITLE + " TEXT, " + CATEGORY_COLUMN_CONTENT + " TEXT, " + CATEGORY_COLUMN_COUNT + " INTEGER );" ;
db.execSQL(DATABASE_CREATE_PROJ);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// TODO Auto-generated method stub
db.execSQL("DROP TABLE IF EXISTS"+ DATABASE_NAME);
onCreate(db);
}
}
public void saveCategoryRecord(Category category) {
String query = "insert into"+ DATABASE_NAME+ " values( ?, ?, ?, ?, ?, ? )";
SQLiteStatement stmt = mDb.compileStatement(query);
stmt.bindString(1, category.getId());
stmt.bindString(2, category.getTitle());
stmt.bindString(3, category.getContent());
stmt.bindString(4, category.getCount());
stmt.execute();
}
public Cursor fetchAllProjects() {
// TODO Auto-generated method stub
return mDb.query(DATABASE_TABLE_PROJ, new String[] {CATEGORY_COLUMN_ID, CATEGORY_COLUMN_TITLE, CATEGORY_COLUMN_CONTENT, CATEGORY_COLUMN_COUNT }, null, null, null, null, null);
}
public GinfyDbAdapter(Context ctx) {
this.mCtx = ctx;
}
public GinfyDbAdapter open() throws SQLException {
mDbHelper = new DatabaseHelper(mCtx);
mDb = mDbHelper.getWritableDatabase();
return this;
}
}
我的代码是否正确，将json数据发送到数据库并显示在listview
中Logcat错误是
07-05 08:59:57.605: E/AndroidRuntime(30062): FATAL EXCEPTION: main
07-05 08:59:57.605: E/AndroidRuntime(30062): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.jsonandroid/com.example.jsonandroid.MainActivity}: java.lang.NullPointerException
07-05 08:59:57.605: E/AndroidRuntime(30062): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
07-05 08:59:57.605: E/AndroidRuntime(30062): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
07-05 08:59:57.605: E/AndroidRuntime(30062): at android.app.ActivityThread.access$600(ActivityThread.java:141)
07-05 08:59:57.605: E/AndroidRuntime(30062): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
07-05 08:59:57.605: E/AndroidRuntime(30062): at android.os.Handler.dispatchMessage(Handler.java:99)
07-05 08:59:57.605: E/AndroidRuntime(30062): at android.os.Looper.loop(Looper.java:137)
07-05 08:59:57.605: E/AndroidRuntime(30062): at android.app.ActivityThread.main(ActivityThread.java:5039)
07-05 08:59:57.605: E/AndroidRuntime(30062): at java.lang.reflect.Method.invokeNative(Native Method)
07-05 08:59:57.605: E/AndroidRuntime(30062): at java.lang.reflect.Method.invoke(Method.java:511)
07-05 08:59:57.605: E/AndroidRuntime(30062): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
07-05 08:59:57.605: E/AndroidRuntime(30062): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
07-05 08:59:57.605: E/AndroidRuntime(30062): at dalvik.system.NativeStart.main(Native Method)
07-05 08:59:57.605: E/AndroidRuntime(30062): Caused by: java.lang.NullPointerException
07-05 08:59:57.605: E/AndroidRuntime(30062): at android.app.Activity.registerForContextMenu(Activity.java:2857)
07-05 08:59:57.605: E/AndroidRuntime(30062): at com.example.jsonandroid.MainActivity.onCreate(MainActivity.java:68)
07-05 08:59:57.605: E/AndroidRuntime(30062): at android.app.Activity.performCreate(Activity.java:5104)
07-05 08:59:57.605: E/AndroidRuntime(30062): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
07-05 08:59:57.605: E/AndroidRuntime(30062): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
答案 0 :(得分：1)
您的课程不会延长ListActivity。
registerForContextMenu(getListView());
http://developer.android.com/reference/android/app/ListActivity.html#getListView()
public ListView getListView ()
获取活动的列表视图小部件。
你有这个可以删除。
private View getListView() {
// TODO Auto-generated method stub
return null; // returning null
}
你也有这个
lv1 =(ListView)findViewById(R.id.list);
lv =(ListView)findViewById(R.id.list);
两者都引用相同的资源ID。
根据你的评论，你说你得到了
java.lang.RuntimeException: Your content must have a ListView whose id attribute is 'android.R.id.list
您自己的视图必须包含一个ID为“@android：id / list”的ListView对象（如果它在代码中则列出）
<ListView
android:id="@android:id/list" // must have this
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#00FF00"
android:layout_weight="1"
android:drawSelectorOnTop="false"/>
编辑：
public class MainActivity extends ListActivity{// implements FetchDataListener,OnClickListener{
private GinfyDbAdapter mDbHelper;
JSONArray contacts = null;
private SimpleCursorAdapter dataAdapter;
@Override
protected void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mDbHelper=new GinfyDbAdapter(MainActivity.this);
mDbHelper.open();
Cursor projectsCursor = mDbHelper.fetchAllProjects();
if(projectsCursor!=null)
{
fillData(projectsCursor);
}
else
{
new GetDataAsyncTask().execute();
}
}
private class GetDataAsyncTask extends AsyncTask<Void, Void, Void> {
private ProgressDialog Dialog = new ProgressDialog(MainActivity.this);
protected void onPreExecute() {
Dialog.setMessage("Loading.....");
Dialog.show();
}
@Override
protected void onPostExecute(Void result) {
super.onPostExecute(result);
Dialog.dismiss();
Cursor projectsCursor = mDbHelper.fetchAllProjects();
if(projectsCursor!=null)
{
mDbHelper=new GinfyDbAdapter(MainActivity.this);
mDbHelper.open();
fillData(projectsCursor);
}
}
@Override
protected Void doInBackground(Void... params) {
getData();
return null;
}
}
public void getData()
{
try
{
HttpClient httpclient = new DefaultHttpClient();
httpclient.getParams().setParameter(CoreProtocolPNames.PROTOCOL_VERSION, HttpVersion.HTTP_1_1);
HttpGet request = new HttpGet("http://www.ginfy.com/api/v1/posts.json");
// HttpGet request = new HttpGet("http://gdata.youtube.com/feeds/api/users/mbbangalore/uploads?v=2&alt=jsonc");
HttpResponse response = httpclient.execute(request);
HttpEntity resEntity = response.getEntity();
String _response=EntityUtils.toString(resEntity); // content will be consume only once
Log.i("................",_response);
httpclient.getConnectionManager().shutdown();
JSONObject jsonObject = new JSONObject(_response);
JSONArray contacts = jsonObject.getJSONArray("post");//(url);
for(int i = 0; i < contacts.length(); i++){
JSONObject c = contacts.getJSONObject(i);
String id = c.getString("id");
String title = c.getString("title");
String content = c.getString("content");
String count = c.getString("content");
mDbHelper=new GinfyDbAdapter(MainActivity.this);
mDbHelper.open();
mDbHelper.saveCategoryRecord(new Category(id,title,content,count));
}
} catch (Exception e) {
e.printStackTrace();
}
}
@SuppressWarnings("deprecation")
private void fillData(Cursor projectsCursor) {
//mDbHelper.open();
if(projectsCursor!=null)
{
String[] from = new String[]{GinfyDbAdapter.CATEGORY_COLUMN_TITLE, GinfyDbAdapter.CATEGORY_COLUMN_CONTENT, GinfyDbAdapter.CATEGORY_COLUMN_COUNT};
int[] to = new int[]{R.id.textView1, R.id.textView2, R.id.textView3};
dataAdapter = new SimpleCursorAdapter(
this, R.layout.activity_row,
projectsCursor,
from,
to,
0);
setListAdapter(dataAdapter);
}else
{
Log.i("...........","null");
}
}
}
数据库类的其他更改
void saveCategoryRecord(Category category) {
/// SQLiteDatabase db = this.getWritableDatabase();
ContentValues values = new ContentValues();
values.put(CATEGORY_COLUMN_TITLE , category.getTitle());
values.put(CATEGORY_COLUMN_CONTENT, category.getContent());
values.put(CATEGORY_COLUMN_COUNT, category.getCount());
// Inserting Row
mDb.insert(DATABASE_TABLE_PROJ, null, values);
mDb.close(); // Closing database connection
}
答案 1 :(得分：0)
从ListActivity扩展您的活动