Question

我只是试图将复选框的状态存储在数据库中，但是当我点击提交按钮时我的应用程序崩溃。我正在尝试使用sqliteOpenHelper执行此操作。存储状态后我也想显示它，但首先我无法存储它。请指导我，因为我是android的新手。这是我的代码..

MainActivity.java

public class DatabaseHelper extends SQLiteOpenHelper {

    public static final String DATABASE_NAME = "check.db";
    public static final String TABLE_NAME = "entry";
    public static final String COL1 = "SIZE";

    public DatabaseHelper(Context context) {
       super(context, DATABASE_NAME, null, 1);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        String createTable = "CREATE TABLE " + TABLE_NAME + "(SIZE INTEGER)";
        db.execSQL(createTable);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) 
   {
    db.execSQL("DROP IF TABLE EXISTS " + TABLE_NAME);
    onCreate(db);
   }

   public boolean addData(int s1){
       SQLiteDatabase db = this.getWritableDatabase();

       ContentValues contentValues = new ContentValues();
       contentValues.put(COL1, s1);

       long result  = db.insert(TABLE_NAME, null, contentValues);

       if(result == -1){
           return false;
       }else{
           return true;
       }
   }
}

databasehelper.java

05-28 19:06:06.236 3806-3806/com.example.hp.checkbox E/AndroidRuntime: FATAL EXCEPTION: main Process: com.example.hp.checkbox, PID: 3806 java.lang.NullPointerException: Attempt to invoke virtual method 'booleancom.example.hp.checkbox.DatabaseHelper.addData(java.lang.String)' on a null object reference
    at com.example.hp.checkbox.MainActivity$2.onClick(MainActivity.java:55)
    at android.view.View.performClick(View.java:5637)
    at android.view.View$PerformClick.run(View.java:22429)
    at android.os.Handler.handleCallback(Handler.java:751)
    at android.os.Handler.dispatchMessage(Handler.java:95)

logcat的

{{1}}

Answer 1

你不应该把这个复选框的事件监听器放在提交按钮onClick监听器上。

Answer 2

我有一些问题我建议尝试使用以下代码，它将侦听器分开而不是将它们包含起来（只有在点击提交按钮时才会应用checkChanged，因为它太晚了无论状态如何（直到你更改复选框））。

期待， “但我怎么知道它添加了一行？” 方法logData已添加到 DatabaseHelper 将列出日志中的行（例如，从数据库中获取数据的介绍）。

MainActivity： -

公共类MainActivity扩展了AppCompatActivity {

CheckBox ch1;
Button btnSubmit;
int checked=0;
DatabaseHelper dbhelper;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    dbhelper = new DatabaseHelper(this); //<<<< ADDED

    ch1=(CheckBox)findViewById(R.id.checkBox);
    btnSubmit=(Button)findViewById(R.id.button);

    // Button onClick Listener
    btnSubmit.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {

            dbhelper.addData(checked);
            dbhelper.logData(); //<<<< ADDED to display data to log (see logData in DatabaseHelper)
        }
    });

    // CheckBox onchanged Listener
    ch1.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
        @Override
        public void onCheckedChanged(CompoundButton compoundButton, boolean isChecked) {
            checked = 0;
            if (isChecked) {
                checked = 1;
            }
        }
    });
    //AddData(); //REMOVED
}

DatabaseHelper.java： -

public class DatabaseHelper extends SQLiteOpenHelper {

    public static final String DATABASE_NAME = "check.db";
    public static final String TABLE_NAME = "entry";
    public static final String COL1 = "SIZE";

    public DatabaseHelper(Context context) {
        super(context, DATABASE_NAME, null, 1);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        //String createTable = "CREATE TABLE " + TABLE_NAME + "(SIZE INTEGER)";
        String createTable = "CREATE TABLE " + TABLE_NAME + "(" + COL1 + " INTEGER)"; //<<<< Suggestion
        db.execSQL(createTable);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion)
    {
        //db.execSQL("DROP IF TABLE EXISTS " + TABLE_NAME); //<<<< INVALID
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME); //<<<< ADDED CORRECTION
        onCreate(db);
    }

    public boolean addData(int s1){
        SQLiteDatabase db = this.getWritableDatabase();

        ContentValues contentValues = new ContentValues();
        contentValues.put(COL1, s1);

        //<<<< simplified return
        return (db.insert(TABLE_NAME, null, contentValues) > 0);
    }

    //<<<<<<<<<< New method to write contents to the log >>>>>>>>>>
    public void logData() {
        SQLiteDatabase db = this.getWritableDatabase();
        Cursor csr =  db.query(TABLE_NAME,null,null,null, null,null, null);
        Log.d(
                "ENTRY TABLE INFO",
                "Number of rows in table is " +
                        csr.getCount() +
                        "; they are :-"
        );
        while (csr.moveToNext()) {
            Log.d(
                    "ENTRY TABLE INFO",
                    "Row # " +
                            String.valueOf(csr.getPosition()) +
                            " that has a value of " +
                            csr.getInt(csr.getColumnIndex(COL1))
            );
        }
        csr.close();
    }
}

测试结果

执行以下操作后： -

单击提交按钮（未选中复选框）。
选中复选框。
点击提交按钮（选中复选框）。

日志中的结果输出为： -

05-28 21:47:40.628 1156-1156/ci.checkit D/ENTRY TABLE INFO: Number of rows in table is 2; they are :-
    Row # 0 that has a value of 0
    Row # 1 that has a value of 1

只需将复选框状态存储到sqlite数据库

2 个答案:

MainActivity： -

DatabaseHelper.java： -

测试结果