Android 固定凭据登录表单实现与常见错误规避

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <!-- 假设这里有一个ImageView，实际应用中可以替换为Logo等 -->
    <ImageView
        android:id="@+id/imageView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="64dp"
        android:src="@drawable/ic_launcher_foreground"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <!-- 用户名输入框 -->
    <EditText
        android:id="@+id/etUsername"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginTop="48dp"
        android:ems="10"
        android:hint="@string/username"
        android:inputType="textPersonName"
        app:layout_constraintEnd_toStartOf="@+id/guideline2"
        app:layout_constraintStart_toStartOf="@+id/guideline"
        app:layout_constraintTop_toBottomOf="@+id/imageView" />

    <!-- 密码输入框 -->
    <EditText
        android:id="@+id/etPassword"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginTop="15dp"
        android:ems="10"
        android:hint="@string/password"
        android:inputType="textPassword"
        app:layout_constraintEnd_toStartOf="@+id/guideline2"
        app:layout_constraintStart_toStartOf="@+id/guideline"
        app:layout_constraintTop_toBottomOf="@+id/etUsername" />

    <!-- 登录按钮 -->
    <Button
        android:id="@+id/btnLogin"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginTop="36dp"
        android:backgroundTint="@color/yellow_700"
        android:text="@string/enterApp"
        app:layout_constraintEnd_toStartOf="@+id/guideline2"
        app:layout_constraintHorizontal_bias="0.495"
        app:layout_constraintStart_toStartOf="@+id/guideline"
        app:layout_constraintTop_toBottomOf="@+id/etPassword" />

    <!-- 辅助线，用于布局对齐 -->
    <androidx.constraintlayout.widget.Guideline
        android:id="@+id/guideline"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="vertical"
        app:layout_constraintGuide_percent="0.1" />

    <androidx.constraintlayout.widget.Guideline
        android:id="@+id/guideline2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="vertical"
        app:layout_constraintGuide_percent="0.9" />

</androidx.constraintlayout.widget.ConstraintLayout>

// 错误示例：过早获取输入框内容
String user = etUsername.getText().toString(); // 此时输入框为空
String pass = etPassword.getText().toString(); // 此时输入框为空

package com.example.your_app_package; // 替换为您的应用包名

import androidx.appcompat.app.AppCompatActivity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

    private Button btnLogin;
    private EditText etUsername;
    private EditText etPassword;

    // 预设的用户名和密码（仅用于演示，生产环境应避免硬编码）
    private final String fixedUsername = "bartul";
    private final String fixedPassword = "kalinic";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // 初始化 UI 组件
        btnLogin = findViewById(R.id.btnLogin);
        etUsername = findViewById(R.id.etUsername);
        etPassword = findViewById(R.id.etPassword);

        // 设置登录按钮的点击监听器
        btnLogin.setOnClickListener(new View.OnClickListener(){
            @Override
            public void onClick(View view) {
                // 在点击事件发生时获取用户输入，这是关键！
                String enteredUsername = etUsername.getText().toString();
                String enteredPassword = etPassword.getText().toString();

                // 验证用户名和密码
                if (enteredUsername.equals(fixedUsername) && enteredPassword.equals(fixedPassword)) {
                    // 登录成功，跳转到下一个 Activity
                    Toast.makeText(getApplicationContext(), "登录成功！", Toast.LENGTH_SHORT).show();
                    Intent intent = new Intent(MainActivity.this, MiNoteMenuActivity.class);
                    // 设置 Intent 标志，清除当前任务栈并启动新任务
                    intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK | Intent.FLAG_ACTIVITY_NEW_TASK);
                    startActivity(intent);
                } else {
                    // 登录失败，显示错误提示
                    Toast.makeText(getApplicationContext(), "用户名或密码错误，请重试！", Toast.LENGTH_SHORT).show();
                    // 清空输入框，方便用户重新输入
                    etUsername.setText("");
                    etPassword.setText("");
                }
            }
        });
    }
}