Question

我正在尝试在我的activity_main页面上创建一个用户数据库，这样当用户登录该应用程序时，它将引导他们进入下一个主要页面。这是当前的ActivityMain.java文件：

         package com.example.awesomefilebuilder;
import android.content.ContentValues;
import android.content.Intent;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
    public class MainActivity extends Base_Activity {

    public final static String EXTRA_MESSAGE = "com.example.awesomefilebuilder.MESSAGE";
    public final String TAG = "MainActivity";
    public final String edit_message ="Username";
    public static final String DATABASE_NAME = "data";
    public static final String TABLE_NAME = "comments_table";
    public static final String C_ID = "_id";
    public static final String NAME = "name";
    public static final String COMMENT = "comment";
    public static final String EMAIL = "email";
    public static final String TIME = "time";
    public static final String PASSWORD = "password";
    public static final int VERSION = 1;

    View view;
    SQLiteDatabase db;
    DbHelper dbhelper;


    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
    {

        DbHelper dbhelper = new DbHelper(getActivity());
        db = dbhelper.getWritableDatabase();
        view = inflater.inflate(R. layout.activity_main, container,false);


            ContentValues cv = new ContentValues();


        cv.put(DbHelper.NAME, NAME);
        cv.put(DbHelper.COMMENT, COMMENT);
        cv.put(DbHelper.EMAIL, EMAIL);
        cv.put(DbHelper.PASSWORD, PASSWORD);
        db.insert(DbHelper.TABLE_NAME, null, cv);


    Button query = (Button) view.findViewById(R.id.query);
    query.setOnClickListener(new OnClickListener()
    {

        public void onClick(View arg0)
        {
            String [] columns = {DbHelper.NAME, DbHelper.COMMENT, DbHelper.EMAIL};

            Cursor cursor = db.query(DbHelper.TABLE_NAME, null, null, null, null, null, null);
            cursor.moveToFirst();

                while(cursor.moveToNext())
                {
                    String name = cursor.getString(cursor.getColumnIndex(DbHelper.NAME));
                    String comment = cursor.getString(cursor.getColumnIndex(DbHelper.COMMENT));
                    String password = cursor.getString(cursor.getColumnIndex(DbHelper.PASSWORD));
                    String email = cursor.getString(cursor.getColumnIndex(DbHelper.EMAIL));

                    Toast.makeText(getActivity(), "Name = "+ name +"/nComment= "+ comment,Toast.LENGTH_SHORT).show();
                }

                cursor.close();




        }

    });
        return view;


    }


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Log.i(TAG, "onCreate" );

}

@Override
public void onDestroy() {
    super.onDestroy();  // Always call the superclass

    // Stop method tracing that the activity started during onCreate()
    android.os.Debug.stopMethodTracing();
}


/** Called when the user clicks the Send button */
public void sendMessage(View view) {
    Intent intent = new Intent(this, HomePageMain.class);
    EditText editText = (EditText) findViewById(R.id.createpicture);
    String message = editText.getText().toString();
    intent.putExtra(EXTRA_MESSAGE, message);
    startActivity(intent);
    Log.i(TAG, "sendMessage" );
    }

}

我在网站上阅读并了解getActivity（）选项应仅用于片段，但我不想将片段用于简单的用户登录屏幕。我该怎么做才能替换getActivity（）选项，或者只是为了修复错误？此外，我不想连接到一个单独的数据库，即使我只能在我的应用程序中创建数据库时可以使用它，我已经完成了。如果有人需要查看任何额外的编码页面，这将使这更容易解决，请告诉我。提前致谢！：）

Answer 1

这应该可以解决问题。关于getApplication(), getApplicationContext(), getBaseContext() and someClass.this

，这是非常好的答案

DbHelper dbhelper = new DbHelper(getApplicationContext());

Answer 2

您不能在Activity类中使用getActivity（），因为此方法属于Fragment类。在您的情况下，您可以执行以下操作：

DbHelper dbhelper = new DbHelper(this);

或

DbHelper dbhelper = new DbHelper(MainActivity.this);

或

DbHelper dbhelper = new DbHelper(getApplicationContext());

注意： 您在此处粘贴的代码语法错误，因为onCreateView（）不是Activity类的方法，它是Fragment类的方法。您应该使用onCreateView（）方法编写的onCreate（）方法编写代码。 strong text

方法getactivity（）未定义类型Use In activity_main for User Database

2 个答案: