2
不管我對這個listview試圖做什麼，並試圖讓它在每次點擊按鈕時動態更新它都不起作用，並且總是拋出一個NPE。無法讓Listview從數據庫中刷新
代碼如下，我非常歡迎提供幫助。我試過重新查詢，我試過了notifyDataSetChanged，但我會說實話，這只是我的第二個項目，第一個使用數據庫或列表視圖，我會努力。
DatabaseHelper
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.provider.BaseColumns;
import android.util.Log;
public class DatabaseHelper extends SQLiteOpenHelper {
private static final String TAG = DatabaseHelper.class.getSimpleName();
public static final String DATABASE_NAME = "reordermymeds.db";
public static final int DATABASE_VERSION = 3;
public static final String TABLE_NAME = "Medicines";
public static final String C_ID = BaseColumns._ID;
public static final String C_MED_NAME = "med_name";
public static final String TABLE_NAME_SURG = "Surgeries";
public static final String SURGERY_NAME = "sName";
public static final String SURGERY_TEL = "sTel";
public static final String SURGERY_MAIL = "sMail";
public DatabaseHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
// TODO Auto-generated constructor stub
}
@Override
public void onCreate(SQLiteDatabase db) {
// TODO Auto-generated method stub
String sql = String.format("CREATE TABLE %s (%s INTEGER PRIMARY KEY, %s TEXT)", TABLE_NAME, C_ID, C_MED_NAME);
String sql_surg = String.format(
"create table %s (%s int primary key, %s TEXT, %s TEXT, %s TEXT)",
TABLE_NAME_SURG, C_ID, SURGERY_NAME, SURGERY_TEL, SURGERY_MAIL);
Log.d(TAG, "onCreate sql: "+sql);
db.execSQL(sql);
db.execSQL(sql_surg);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// TODO Auto-generated method stub
db.execSQL("drop table if exists " + TABLE_NAME);
db.execSQL("drop table if exists " + TABLE_NAME_SURG);
this.onCreate(db);
}
}
和
活動
import android.app.ListActivity;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.SimpleCursorAdapter;
import android.widget.Toast;
public class pills extends ListActivity {
public static final String C_MED_NAME = "med_name";
public SimpleCursorAdapter ladapter;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.pills);
try {
DatabaseHelper DBHelper= new DatabaseHelper(this);
SQLiteDatabase db = DBHelper.getReadableDatabase();
Cursor cur = db.query("Medicines", null, null, null, null, null, null);
startManagingCursor(cur);
String [] columns = new String[] {C_MED_NAME};
int [] to = new int[] {R.id.meditem};
SimpleCursorAdapter ladapter = new SimpleCursorAdapter(this, R.layout.meditem, cur, columns, to);
this.setListAdapter(ladapter);
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
Button saveMed = (Button) findViewById(R.id.pills_newmedsubmit);
saveMed.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
final EditText newMed = (EditText) findViewById(R.id.pills_newmedtxtbox);
if (newMed.getText().toString().equals("")) {
Context context = getApplicationContext();
CharSequence text = "Please type the name of a new prescription item.";
int duration = Toast.LENGTH_SHORT;
Toast toast= Toast.makeText(context, text, duration);
toast.show();
}
else
{
String medName = newMed.getText().toString();
insertNewPrescriptionItem(medName);
EditText clearTextBox = (EditText) findViewById(R.id.pills_newmedtxtbox);
clearTextBox.setText("");
Context context = getApplicationContext();
CharSequence text = "Saved";
int duration = Toast.LENGTH_SHORT;
Toast toast = Toast.makeText(context, text, duration);
toast.show();
}
setListAdapter(ladapter);
ladapter.notifyDataSetChanged();
}
});}
private void insertNewPrescriptionItem (String medName){
DatabaseHelper DbHelper = new DatabaseHelper(this);
SQLiteDatabase db = DbHelper.getWritableDatabase();
ContentValues cv = new ContentValues();
cv.put(DatabaseHelper.C_MED_NAME, medName);
db.insert(DatabaseHelper.TABLE_NAME, DatabaseHelper.C_MED_NAME, cv);
db.close();
}
}
當然，最後但並非最不重要的，堆棧跟蹤。我可以看到該錯誤，但我嘗試使用Google的每一個結果都是一樣的。任何人都可以證明我是否一定會出現愚蠢的錯誤？
堆棧跟蹤
08-11 01:21:26.095: ERROR/AndroidRuntime(15327): FATAL EXCEPTION: main
08-11 01:21:26.095: ERROR/AndroidRuntime(15327): java.lang.NullPointerException
08-11 01:21:26.095: ERROR/AndroidRuntime(15327): at com.asurya.reordmymeds.pills$1.onClick(pills.java:90)
08-11 01:21:26.095: ERROR/AndroidRuntime(15327): at android.view.View.performClick(View.java:2485)
08-11 01:21:26.095: ERROR/AndroidRuntime(15327): at android.view.View$PerformClick.run(View.java:9080)
08-11 01:21:26.095: ERROR/AndroidRuntime(15327): at android.os.Handler.handleCallback(Handler.java:587)
08-11 01:21:26.095: ERROR/AndroidRuntime(15327): at android.os.Handler.dispatchMessage(Handler.java:92)
08-11 01:21:26.095: ERROR/AndroidRuntime(15327): at android.os.Looper.loop(Looper.java:130)
08-11 01:21:26.095: ERROR/AndroidRuntime(15327): at android.app.ActivityThread.main(ActivityThread.java:3683)
08-11 01:21:26.095: ERROR/AndroidRuntime(15327): at java.lang.reflect.Method.invokeNative(Native Method)
08-11 01:21:26.095: ERROR/AndroidRuntime(15327): at java.lang.reflect.Method.invoke(Method.java:507)
08-11 01:21:26.095: ERROR/AndroidRuntime(15327): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
08-11 01:21:26.095: ERROR/AndroidRuntime(15327): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
08-11 01:21:26.095: ERROR/AndroidRuntime(15327): at dalvik.system.NativeStart.main(Native Method)
08-11 01:21:26.107: WARN/ActivityManager(110): Force finishing activity com.asurya.reordmymeds/.pills
哎呀。如果我讓大家都知道這會幫助，與其指望他們自己:)
的代碼這是造成NPE是行：
ladapter.notifyDataSetChanged();
另外，如果我只是註釋掉該行，該應用程序運行正常，但您必須刷新活動以查看數據庫中的更新數據。謝謝大家。
哪條線是'90'？ –
糟糕。如果我讓你們都知道，而不是自己計算它們，它會有所幫助:)導致NPE的代碼行是ladapter.notifyDataSetChanged（）;另外，如果我只是註釋掉這一行，應用程序運行良好，但您必須刷新活動以查看數據庫中的更新數據。謝謝大家。 –