我有一个快速的问题，我敢肯定我只是犯了一个小错误，但我无法弄清楚。我试图根据用户在EditText中输入的内容从数据库中获取信息。我出错了
“ java.lang.IllegalStateException：无法从读取行0，列1
CursorWindow。确保游标已正确初始化，然后再进行
从中访问数据。”。
这是我的主要活动课
public class MainActivity extends AppCompatActivity {
Button create;
Button retrieve;
Button save;
Button clear;
EditText listName;
EditText listDetails;
ToDoListDatabase myDb;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
myDb = new ToDoListDatabase(this);
create = (Button)findViewById(R.id.createButton);
retrieve = (Button)findViewById(R.id.retrieveButton);
save = (Button)findViewById(R.id.saveButton);
clear = (Button)findViewById(R.id.clearButton);
listName = (EditText)findViewById(R.id.listName);
listDetails = (EditText)findViewById(R.id.listDetails);
create.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
AddList();
}
});
retrieve.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
showList(listName.getText().toString());
}
});
}
//Method Resets EditText back to default
public void resetEditText(){
listName.setText("");
listDetails.setText("");
}
//Method Adds List Entered By User To DataBase
public void AddList(){
boolean isInserted = myDb.insertData(listName.getText().toString(), listDetails.getText().toString());
if(isInserted == true){
Toast.makeText(MainActivity.this,"List " + listName.getText().toString() + " successfully created", Toast.LENGTH_LONG).show();
resetEditText();
}
else
Toast.makeText(MainActivity.this,"Error creating list", Toast.LENGTH_LONG).show();
}
public void showList(String listName){
Cursor res = myDb.getList(listName);
if(res.getCount() == 0){
Toast.makeText(MainActivity.this,"Error finding list", Toast.LENGTH_LONG).show();
return;
}
StringBuffer buffer = new StringBuffer();
buffer.append(res.getString(2));
listDetails.setText(buffer); //Not working yet!!!!
}
}
这是我的数据库类
public class ToDoListDatabase extends SQLiteOpenHelper {
public static final String DATABASE_NAME = "List_db";
public static final String TABLE_NAME = "List_Table";
public static final String COL_1 = "ID";
public static final String COL_2 = "NAME";
public static final String COL_3 = "LIST";
public ToDoListDatabase(Context context) {
super(context, DATABASE_NAME, null, 1);
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL("create table " + TABLE_NAME + " (ID INTEGER PRIMARY KEY AUTOINCREMENT,NAME TEXT,LIST TEXT)");
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("DROP TABLE IF EXITS" + TABLE_NAME);
onCreate(db);
}
public boolean insertData(String name, String list) {
SQLiteDatabase db = this.getWritableDatabase();
ContentValues contentValues = new ContentValues();
contentValues.put(COL_2, name);
contentValues.put(COL_3, list);
long result = db.insert(TABLE_NAME, null, contentValues);
if (result == -1) { //returns -1 if not inserted
return false;
} else
return true;
}
public Cursor getList(String listName) {
SQLiteDatabase db = this.getWritableDatabase();
Cursor res = db.rawQuery("SELECT LIST FROM " + TABLE_NAME + " WHERE NAME = '" +listName+"'" , null);
return res;
}
}
这是我的Android显示器
10-10 13:11:41.618 2643-2643/com.example.stephen.todolist E/AndroidRuntime: FATAL EXCEPTION: main
android.database.CursorIndexOutOfBoundsException: Index -1 requested, with a size of 4
at android.database.AbstractCursor.checkPosition(AbstractCursor.java:424)
at android.database.AbstractWindowedCursor.checkPosition(AbstractWindowedCursor.java:136)
at android.database.AbstractWindowedCursor.getString(AbstractWindowedCursor.java:50)
at com.example.stephen.todolist.MainActivity.showList(MainActivity.java:79)
at com.example.stephen.todolist.MainActivity$2.onClick(MainActivity.java:47)
at android.view.View.performClick(View.java:4439)
at android.widget.Button.performClick(Button.java:139)
at android.view.View$PerformClick.run(View.java:18395)
at android.os.Handler.handleCallback(Handler.java:725)
at android.os.Handler.dispatchMessage(Handler.java:92)
at android.os.Looper.loop(Looper.java:176)
at android.app.ActivityThread.main(ActivityThread.java:5317)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1102)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:869)
at dalvik.system.NativeStart.main(Native Method)
最佳答案
您的ToDoListDatabase类不包含任何名称为listName的字段，您将在该字段上调用getText（）。另外，您没有在getList（）中传递任何参数。您应该在此getList（）中传递EditText查询，然后在此参数上创建查询。
变化：
MainActivy.java
retrieve.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
showList(listName.getText().toString());
}
});
public void showList(String listName){
Cursor res = myDb.getList(listName);
if(res.getCount() == 0){
Toast.makeText(MainActivity.this,"Error finding list", Toast.LENGTH_LONG).show();
//return;
}
}
StringBuffer buffer = new StringBuffer();
buffer.append(res.getString(2));
listDetails.setText(buffer); //Not working yet!!!!
}
ToDoListDatabase.java
public Cursor getList(String listName) {
SQLiteDatabase db = this.getWritableDatabase();
Cursor res = db.rawQuery("SELECT LIST FROM " + TABLE_NAME + " WHERE NAME ='" + listName+"'" , null);
return res;
}
更新资料
将您的showList更改为
public void showList(String listName){
Cursor res = myDb.getList(listName);
if(res.getCount() == 0){
Toast.makeText(MainActivity.this,"Error finding list", Toast.LENGTH_LONG).show();
return;
}
res.moveToFirst();
StringBuffer buffer = new StringBuffer();
while (!res.isAfterLast()) {
buffer.append(res.getString(0));
res.moveToNext();
}
res.close();
listDetails.setText(buffer); //Not working yet!!!!
}