Android SharedPreferences 登錄頁面：Manifest 缺少主 Activity 聲明導致啟動即結束，修正包結構與上下文傳遞

核心錯誤：AndroidManifest.xml 缺少 MAIN/LAUNCHER Activity

<activity android:name="my" android:label="mine">  
    <intent-filter>
        <action android:name="android.intent.action.MAIN" />
        <category android:name="android.intent.category.LAUNCHER" />
    </intent-filter>
</activity>

android:name="my" 應為完整類名 com.example.manage.MainActivity，否則系統找不到入口，**安裝成功但圖標啟動即結束**（ActivityManager 無法解析組件）。

完整修正版代碼

1. AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="https://schemas.android.com/apk/res/android"
    package="com.example.manage"
    android:versionCode="1"
    android:versionName="1.0">

    <uses-sdk android:minSdkVersion="8" android:targetSdkVersion="17" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme">

        <activity
            android:name=".MainActivity"  
            android:label="@string/app_name">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

    </application>
</manifest>

2. MainActivity.java（修正上下文傳遞、泛型、監聽器類型）

package com.example.manage;

import android.app.Activity;
import android.os.Bundle;
import android.text.TextUtils;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
import java.util.Map;

public class MainActivity extends Activity implements View.OnClickListener {
    private EditText etNumber, etPassword;
    private Button btnLogin;

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

    private void initView() {
        etNumber = findViewById(R.id.et_number);
        etPassword = findViewById(R.id.et_password);
        btnLogin = findViewById(R.id.btn_login);
        btnLogin.setOnClickListener(this);  // 直接 this，實現了 OnClickListener
    }

    private void loadSavedInfo() {
        Map<String, String> userInfo = Utils.getUserInfo(this);
        if (userInfo != null) {
            etNumber.setText(userInfo.get("number"));
            etPassword.setText(userInfo.get("password"));
        }
    }

    @Override
    public void onClick(View v) {
        if (v.getId() == R.id.btn_login) {
            String number = etNumber.getText().toString().trim();
            String password = etPassword.getText().toString();
            if (TextUtils.isEmpty(number)) { toast("請輸入賬號"); return; }
            if (TextUtils.isEmpty(password)) { toast("請輸入密碼"); return; }
            
            toast("登錄成功");
            Log.i("MainActivity", "記住密碼: " + number + ", " + password);
            Utils.saveUserInfo(this, number, password);
        }
    }

    private void toast(String msg) {
        Toast.makeText(this, msg, Toast.LENGTH_SHORT).show();
    }
}

3. Utils.java（修正泛型、鍵名一致、上下文類型）

package com.example.manage;

import android.content.Context;
import android.content.SharedPreferences;
import java.util.HashMap;
import java.util.Map;

public class Utils {
    private static final String PREFS_NAME = "data";
    private static final String KEY_USER = "username";
    private static final String KEY_PWD = "pwd";

    public static boolean saveUserInfo(Context context, String number, String password) {
        SharedPreferences sp = context.getSharedPreferences(PREFS_NAME, Context.MODE_PRIVATE);
        sp.edit().putString(KEY_USER, number).putString(KEY_PWD, password).apply();
        return true;
    }

    public static Map<String, String> getUserInfo(Context context) {
        SharedPreferences sp = context.getSharedPreferences(PREFS_NAME, Context.MODE_PRIVATE);
        String number = sp.getString(KEY_USER, "");
        String password = sp.getString(KEY_PWD, "");
        if (TextUtils.isEmpty(number) && TextUtils.isEmpty(password)) return null;
        Map<String, String> map = new HashMap<>();
        map.put("number", number);
        map.put("password", password);
        return map;
    }
}

關鍵修正點總結

「Manifest 入口類名寫全、SharedPreferences 鍵值對齊、上下文傳 this 不傳 Application」—— Android 登錄頁三大填坑指南。