java - 登录后在抽屉导航中显示电子邮件

Question

我试图在登录 Android 应用程序后在抽屉导航中显示来自 login.java 页面的电子邮件。运行时出现 FATAL EXCEPTION 错误和 java.lang.NullPointerException 。

我已将代码放入DoctorHome.java:

package com.example.medicationmanagementsystem;

import android.content.Intent;
import android.os.Bundle;
import android.view.MenuItem;
import android.widget.EditText;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.appcompat.app.ActionBarDrawerToggle;
import androidx.appcompat.app.AppCompatActivity;
import androidx.appcompat.widget.Toolbar;
import androidx.core.view.GravityCompat;
import androidx.drawerlayout.widget.DrawerLayout;

import com.example.medicationmanagementsystem.DAO.DatabaseHelper;
import com.google.android.material.navigation.NavigationView;

public class DoctorHome extends AppCompatActivity implements NavigationView.OnNavigationItemSelectedListener {
    private DrawerLayout drawer;
    TextView txtDisplayEmail;
    DatabaseHelper myDb;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.doctor_layout);

        Toolbar toolbar = findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);


        drawer = findViewById(R.id.drawer_layout);

        txtDisplayEmail = findViewById(R.id.emaildisplay);
        txtDisplayEmail.setText(myDb.getEmail());

        NavigationView navigationView = findViewById(R.id.nav_view);
        navigationView.setNavigationItemSelectedListener(this);

        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(this, drawer, toolbar,
                R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        drawer.addDrawerListener(toggle);
        toggle.syncState();
    }
    //END

    @Override
    public boolean onNavigationItemSelected(@NonNull MenuItem menuItem) {
        switch (menuItem.getItemId()) {
            case R.id.nav_createprescription:
                Intent createpresintent = new Intent(DoctorHome.this, MainActivity.class);
                startActivity(createpresintent);
                break;
            case R.id.viewprescriptions:
                Intent presintent = new Intent(DoctorHome.this, ViewListContents.class);
                startActivity(presintent);
                break;
            case R.id.nav_addpatients:
                Intent createpatientintent = new Intent(DoctorHome.this, NewPatient.class);
                startActivity(createpatientintent);
                break;
            case R.id.nav_viewpatients:
                Intent viewpatientintent = new Intent(DoctorHome.this, ViewPatientListContents.class);
                startActivity(viewpatientintent);
                break;
            case R.id.nav_logout:
                Intent logoutintent= new Intent(DoctorHome.this, Login.class);
                startActivity(logoutintent);
                break;
        }
        drawer.closeDrawer(GravityCompat.START);
        return true;
    }

    @Override
    public void onBackPressed() {
        if (drawer.isDrawerOpen(GravityCompat.START)) {
            drawer.closeDrawer(GravityCompat.START);
        } else {
            super.onBackPressed();
        }
    }
}

DatabaseHelper.java

//getting email
    public String getEmail() throws SQLException {
        String email = "";
        Cursor cursor = this.getReadableDatabase().query(
                TABLE_USERS, new String[] {COL_USER_EMAIL},
                null, null, null, null, null);
        if (cursor.moveToFirst()) {
            do {
                email = cursor.getString(0);
            } while (cursor.moveToNext());
        }
        cursor.close();

        return email;
    }

我使用 SQLite 作为数据库来保存用户详细信息。我只需要此电子邮件显示在导航标题的 TextView 电子邮件显示中。任何帮助，将不胜感激。谢谢你!!

Answer 1

首先，您必须先初始化myDb，然后才能像这样使用它:

myDb = new DatabaseHelper(this);

此外，txtDisplayEmail 不在您的 Activity 布局内，因此:

txtDisplayEmail = findViewById(R.id.emaildisplay);

返回null。
您应该做的是在 NavigationView 的标题中找到 txtDisplayEmail。
更改为:

myDb = new DatabaseHelper(this);
drawer = findViewById(R.id.drawer_layout);
NavigationView navigationView = findViewById(R.id.nav_view);
View header = navigationView.getHeaderView(0);
txtDisplayEmail = (TextView) header.findViewById(R.id.emaildisplay);
txtDisplayEmail.setText(myDb.getEmail());
navigationView.setNavigationItemSelectedListener(this);

但是 DatabaseHelper 的方法 getEmail() 不会返回用户的电子邮件(如果这是它应该做的)。
它只是循环遍历表中的所有电子邮件并返回最后一封。
因此，将其更改为返回登录用户的电子邮件。