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標(biāo)題: JAVA顯示空指針，請(qǐng)問(wèn)哪里出問(wèn)題了？ [打印本頁(yè)]

作者: Wheat_southwest 時(shí)間: 2014-06-02 22:42
標(biāo)題: JAVA顯示空指針，請(qǐng)問(wèn)哪里出問(wèn)題了？
本帖最后由 Wheat_southwest 于 2014-06-03 07:35 編輯

public class dbhelper extends SQLiteOpenHelper{
private static final String DB_NAME = "school_activity.db";
private static final int DB_VERSION = 1;
private static final String TABLE_NAME1 = "lecture";
private static final String TABLE_NAME2 = "stu";
private static final String TABLE_NAME3 = "com";
private static final String CREATE_INFO1 = "create table if not exists lecture("
         + "_id integer primary key autoincrement,name varchar(20),"
         + "time varchar(20),place varchar(20),hostname varchar(20),"
         +"more varchar(50),contact varchar(20)";
private static final String CREATE_INFO2 = "create table if not exists stu("
         + "_id integer primary key autoincrement,name varchar(20),"
         + "time varchar(20),place varchar(20),hostname varchar(20),"
         +"more varchar(50),contact varchar(20)";
private static final String CREATE_INFO3 = "create table if not exists com("
         + "_id integer primary key autoincrement,name varchar(20),"
         + "time varchar(20),place varchar(20),hostname varchar(20),"
         +"more varchar(50),contact varchar(20)";
private SQLiteDatabase db;
   dbhelper(Context context){
   super(context,DB_NAME,null,DB_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db){
   this.db=db;
   db.execSQL(CREATE_INFO1);
   Log.i("TABLE1","created successfully!");
   db.execSQL(CREATE_INFO2);
   Log.i("TABLE2","created successfully!");
   db.execSQL(CREATE_INFO3);
   Log.i("TABLE3","created successfully!");
}
public void insert(SQLiteDatabase MDB, String tableName) {
   ContentValues values=new ContentValues();
      values.put("name","信管");
      values.put("time","2014.6.1");
      values.put("place","204");
      values.put("hostname","名字");
      values.put("more","關(guān)于安卓編程");
      values.put("contact","名字  手機(jī)");
      MDB.insert(tableName,null,values);
}
public Cursor query(String tableName) {
      db = getWritableDatabase();
      Cursor c = db.query(tableName, null, null, null, null, null, null);
      return c;
}

// Return cursor by SQL string
public Cursor rawQuery(String sql, String[] args) {
      db = getWritableDatabase();
      Cursor c = db.rawQuery(sql, args);
      return c;
}
public void execSQL(String sql) {
      db = getWritableDatabase();
      db.execSQL(sql);
}
public void del(int id,String tableName) {
      if (db == null)
         db = getWritableDatabase();
      db.delete(tableName, "id=?", new String[] { String.valueOf(id) });
}
public void close() {
      if (db != null)
         db.close();
}
public void onUpgrade(SQLiteDatabase db,int oldversion,int newversion){

}

}

public class activities extends Activity {
SQLiteDatabase db=null;
dbhelper dbhelper;
ArrayList<HashMap<String,Object>> listdata;
SimpleAdapter listItemAdapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.ecnu_type);
      dbhelper=new dbhelper(activities.this);
      dbhelper.onCreate(db);
      dbhelper.insert(db,"lecture");
      Cursor cursor=dbhelper.rawQuery("select name,hostname from lecture",null);
      listdata=new ArrayList<HashMap<String, Object>>();
   // cursor.moveToFirst();
      int columnsize=cursor.getColumnCount();
      while(cursor.moveToNext()){

         HashMap<String,Object> map=new HashMap<String, Object>();
         for(int i=0;i<columnsize;i++){
            map.put("name", cursor.getString(1));
            map.put("hostname",cursor.getString(4));

         }
         listdata.add(map);
      }
      ListView list=(ListView)findViewById(R.id.activity_items);
      listItemAdapter=new SimpleAdapter(activities.this,listdata,R.layout.item,new String[]{"name","hostname"},
            new int[]{R.id.name,R.id.hostname});
      list.setAdapter(listItemAdapter);

      }

}

作者: Wheat_southwest 時(shí)間: 2014-06-02 22:46
這是運(yùn)行后的結(jié)果

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