Question

我试图在我的Db中插入一些记录。问题是当我点击保存按钮时我得到了这个例外。所以我首先检查了logcat并过滤掉了这些消息。

    03-21 18:07:00.820: E/AndroidRuntime(4756): FATAL EXCEPTION: main
    03-21 18:07:00.820: E/AndroidRuntime(4756): java.lang.NullPointerException
    03-21 18:07:00.820: E/AndroidRuntime(4756):     at com.example.kjk.MainActivity$1.onClick(MainActivity.java:51)
    03-21 18:07:00.820: E/AndroidRuntime(4756):     at android.view.View.performClick(View.java:4240)
    03-21 18:07:00.820: E/AndroidRuntime(4756):     at android.view.View$PerformClick.run(View.java:17721)
    03-21 18:07:00.820: E/AndroidRuntime(4756):     at android.os.Handler.handleCallback(Handler.java:730)
    03-21 18:07:00.820: E/AndroidRuntime(4756):     at android.os.Handler.dispatchMessage(Handler.java:92)
    03-21 18:07:00.820: E/AndroidRuntime(4756):     at android.os.Looper.loop(Looper.java:137)
    03-21 18:07:00.820: E/AndroidRuntime(4756):     at android.app.ActivityThread.main(ActivityThread.java:5103)
    03-21 18:07:00.820: E/AndroidRuntime(4756):     at java.lang.reflect.Method.invokeNative(Native Method)
    03-21 18:07:00.820: E/AndroidRuntime(4756):     at java.lang.reflect.Method.invoke(Method.java:525)
    03-21 18:07:00.820: E/AndroidRuntime(4756):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
    03-21 18:07:00.820: E/AndroidRuntime(4756):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
    03-21 18:07:00.820: E/AndroidRuntime(4756):     at dalvik.system.NativeStart.main(Native Method)

我认为异常来自这里然而我无法找到解决问题的任何解决方案

AddData（name.getText（）。toString（），surname.getText（）。toString（））;

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    name=(EditText)findViewById(R.id.edtName);
    surname=(EditText)findViewById(R.id.edtsurname);
    btnsave=(Button)findViewById(R.id.btnSave);
    btnfetch=(Button)findViewById(R.id.btnFetch);
    tvname=(TextView)findViewById(R.id.tvNmae);
    tvsurname=(TextView)findViewById(R.id.tvSurname);

    btnsave.setOnClickListener(new View.OnClickListener() {


        @Override
        public void onClick(View v) {
        try {

            AddData(name.getText().toString(), surname.getText().toString());

        } catch (Exception e) {

            Log.e("Error ", e.getMessage());
        }
        finally{

            v1.close();

        }

        }
    });


    btnfetch.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {
        SQLiteDatabase db=v1.getReadableDatabase();
        Cursor cursor=db.query( "Info", columns, null, null, null, null, null);

        while(cursor.moveToNext()){

            String name=cursor.getString(cursor.getColumnIndex("name"));
            String surname=cursor.getString(cursor.getColumnIndex("surname"));
            tvname.setText(name);
            tvsurname.setText(surname);



        }
        }
    });

}

private void AddData(String name,String sur) {
SQLiteDatabase db=v1.getWritableDatabase();
ContentValues cv=new ContentValues();
cv.put(name, sur);
db.insertOrThrow("Info", null, cv);

}

以下是数据库类

private static final String Db_Name="Mydb";
private static final int ver=1;


public Veritabani(Context context, String name, CursorFactory factory,
        int version) {
    super(context, Db_Name, null, ver);
    // TODO Auto-generated constructor stub
}

@Override
public void onCreate(SQLiteDatabase db) {
    // TODO Auto-generated method stub
    db.execSQL("CREATE TABLE Info(name TEXT,surname TEXT);");

}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    // TODO Auto-generated method stub
    db.execSQL("DROP TABLE IF EXIST Info");
    onCreate(db);
}

Answer 1

您的堆栈跟踪说

java.lang.NullPointerException
 03-21 18:07:00.820: E/AndroidRuntime(4756):at com.example.kjk.MainActivity$1.onClick(MainActivity.java:51)

来自您的评论

所以v1是数据库和第51行的实例，表示为 logcat是v1.close（）;

这表示v1为空，并且您尚未正确初始化它。

试

protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
v1 = new Veritabani(this);

Answer 2

尝试将cursor.moveToFirst()放在while(cursor.moveToNext()){}代码中的btnfetch.setOnClickListener之前。

尝试插入记录时出现NullPointerException

2 个答案: