尝试使用光标窗口null异常错误显示ListView时错误

Question

i我试图将目标日期添加到listGditem，目标权重到listGwitem和当前的重量为listCwitem，然后将它们插入SQLITE，并将其显示在Historical Activity.java中。将数据插入设置行为有效，但是显示这些项目的显示以下错误：

引起的： 来自Cursorwindow。确保正确初始化光标 从中访问数据之前。 在android.database.cursorwindow.nativegetstring(本机方法( at android.database.cursorwindow.getstring(cursorwindow.java:438( at Android.database.AbstractwindowedCursor.getString(AbstractWindowedCursor.java:51(
在com.example.fftest.thistoryactivity.viewdata(historyActivity.java:121(
在com.example.fftest.thistoryactivity.oncreate(historyActivity.java:85(

历史法

public class historyActivity extends MainActivity {
    private TextView mTextMessage;
    Intent intent = new Intent();
    ListView listView1;
    ListView listView2;
    ListView listView3;
    ArrayList<String> listgDitem;
    ArrayList<String> listgWitem;
    ArrayList<String> listcWitem;
Cursor cursor;
EditText goalDinput;
    EditText goalWinput;
    EditText currentWinput;

    DatabaseHelper myDB;
    private BottomNavigationView.OnNavigationItemSelectedListener mOnNavigationItemSelectedListener
            = new BottomNavigationView.OnNavigationItemSelectedListener() {
        @Override
        public boolean onNavigationItemSelected(@NonNull MenuItem item) {
            switch (item.getItemId()) {
                case R.id.navigation_home:
                    mTextMessage.setText(R.string.title_home);
                    Intent intent1 = new Intent(historyActivity.this, MainActivity.class);
                    startActivity(intent1);
                    break;
                case R.id.navigation_history:
                    mTextMessage.setText(R.string.title_history);
                    Intent intent2 = new Intent(historyActivity.this, historyActivity.class);
                    startActivity(intent2);
                    break;
                case R.id.navigation_progress:
                    mTextMessage.setText(R.string.title_progress);
                    Intent intent3 = new Intent(historyActivity.this, progressActivity.class);
                    startActivity(intent3);
                    break;
                case R.id.navigation_settings:
                    mTextMessage.setText(R.string.title_settings);
                    Intent intent4 = new Intent(historyActivity.this, settingsActivity.class);
                    startActivity(intent4);
                    break;
            }
            return false;
        }
    };
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_history);
        goalDinput = findViewById(R.id.goaldinput);
        goalWinput = findViewById(R.id.goalwinput);
        currentWinput = findViewById(R.id.currentWinput);
        listView1=findViewById(R.id.goaldlistView);
        listView2=findViewById(R.id.goalwlistView);
        listView3=findViewById(R.id.currentwlistView);
        viewData();
        listView1.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
                String text = listView1.getItemAtPosition(i).toString();
                Toast.makeText(historyActivity.this,"" + text, Toast.LENGTH_SHORT).show();
            }
        });
        listView2.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
                String text = listView2.getItemAtPosition(i).toString();
                Toast.makeText(historyActivity.this,"" + text, Toast.LENGTH_SHORT).show();
            }
        });
        listView3.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
                String text = listView3.getItemAtPosition(i).toString();
                Toast.makeText(historyActivity.this,"" + text, Toast.LENGTH_SHORT).show();
            }
        });
    }
    private void viewData() {
        myDB = new DatabaseHelper(this);
        listgDitem=new ArrayList<>();
        listgWitem=new ArrayList<>();
        listcWitem=new ArrayList<>();
        cursor = myDB.viewData();
        if (cursor.getCount() == 0) {
            Toast.makeText(this, "No data to show", Toast.LENGTH_SHORT).show();
        } else {
            while (cursor.moveToNext()) {
                listgDitem.add(cursor.getString(1));
                listgWitem.add(cursor.getString(2));
               listcWitem.add(cursor.getString(3));
            }
            adapter1 = new ArrayAdapter<>(this, R.layout.activity_history, listgDitem);
            adapter2 = new ArrayAdapter<>(this, R.layout.activity_history, listgWitem);
            adapter3 = new ArrayAdapter<>(this, R.layout.activity_history, listcWitem);
            listView1.setAdapter(adapter1);
            listView2.setAdapter(adapter2);
            listView3.setAdapter(adapter3);
        }
    }

}

databasehelper.java

package com.example.fftest;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.DatabaseErrorHandler;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
public class DatabaseHelper extends SQLiteOpenHelper {
    public static final String DB_NAME="weightDB.db";
    public static final String DB_TABLE="weightDB_data";
    public static final String ID = "ID";
    public static final String Col1 = "GDATE";
    public static final String Col2 = "GWEIGHT";
    public static final String Col3 = "CWEIGHT";
    public static final String CREATE_TABLE="CREATE TABLE " + DB_TABLE + " ("+
            ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " +
             " GDATE TEXT, GWEIGHT TEXT, CWEIGHT " + ") ";
    Cursor cursor;
    public DatabaseHelper(Context ctx)
    {
        super(ctx, DB_NAME, null, 1);}

    @Override
public void onCreate(SQLiteDatabase db){
    db.execSQL(CREATE_TABLE);}
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion){
        db.execSQL("DROP IF TABLE EXISTS "  + DB_TABLE);
        onCreate(db);
    }
    public boolean insertData(String gDate, String gWeight, String cWeight){
        SQLiteDatabase db = this.getWritableDatabase();
        ContentValues contentValues = new ContentValues();
        contentValues.put(Col1, gDate);
        contentValues.put(Col2, gWeight);
        contentValues.put(Col3, cWeight);
        long result = db.insert(DB_TABLE, null, contentValues);
        return result !=-1;
    }
    public Cursor viewData(){
        SQLiteDatabase db = this.getReadableDatabase();
        String query = "SELECT * from " + DB_TABLE;
        cursor = db.rawQuery(query,null);
        return cursor;
    }
}

Answer 1

我可以看到的三件事是您的代码中的可疑/错误，

1.如果您最近更改了CREATE_TABLE模式，则必须在DatabaseHelper.java

上更新DB版本

static final int DB_VERSION = 2;

public DatabaseHelper(Context ctx) {
    super(ctx, DB_NAME, null, DB_VERSION);
}

2.完整的create_table架构找到，最后一部分， CWEIGHT type TEXT in the CREATE_TABLE中错过了。

public static final String CREATE_TABLE="CREATE TABLE " + DB_TABLE + " ("+
        ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " +
         " GDATE TEXT, GWEIGHT TEXT, CWEIGHT " + ") ";

正确的是

public static final String CREATE_TABLE="CREATE TABLE " + DB_TABLE + " ("+
        ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " +
         " GDATE TEXT, GWEIGHT TEXT, CWEIGHT TEXT" + "); ";

3. Onupgrade((方法，带有错误的架构，"如果"位置，

db.execSQL("DROP IF TABLE EXISTS "  + DB_TABLE);

这可能会丢下以下错误，

android.database.sqlite.SQLiteException: near "IF": syntax error

正确的语法为drop表[如果存在] [schema_name。] table_name;因此，您可以更新代码，

db.execSQL("DROP TABLE IF EXISTS "  + DB_TABLE);