无法从SharedPreferences获取值

Question

嘿，这里有人能帮我吗？我想从user.java获取SharedPreferences,但总是得到以下错误：

2020-12-29 16:42:11.424 220 63-22063/com.example.BauwagenApp E/AndroidRuntime：致命异常：主进程：com.example.BauwagenApp,PID：22063 java.lang.RuntimeException：无法启动activity组件Info{com.example.BauwagenApp/com.example.BauwagenApp.ActivityUser}：java.lang.NullPoInterException：尝试在Android.App.ActivityThread.PerformLaunchActivity（ActivityThread.java:3449)上的null对象引用上调用虚拟方法“）在android.os.looper.loop（looper.java:223)在android.app.activitythread.main（activitythread.java:7656)在java.lang.reflect.Method.invoke（原生方法）在com.android.internal.os.runtimeinit$methodandargscaller.run（runtimeinit.java:592)在com.android.internal.os.zygoteinit.main（zygoteinit.java:947)

原因：java.lang.NullPoInterException：尝试在Android.Content.Context.Android.Context.GetApplicationContext(ContextWrapper.Java:122)处的Com.Example.BauwagenApp.User.(user.java:39)处的Com.Example.BauwagenApp.User.(user.java:39)处的Android.App.Activity.PerformCreate（Activity.java:8000)处的Android.Context.Android.Context.GetApplicationContext()对空对象引用html" target="_blank">调用虚拟方法“.ServerTransaction.TransactionExecutor.Execute（TransactionExecutor.java:95)在Android.app.ActivityThread$H.HandleMessage（ActivityThread.java:2066)在Android.os.Handler.DispatchMessage（ActivityThread.java:106)在Android.os.Looper.Loop（Looper.java:223)在Android.app.ActivityThread.Main（ActivityThread.java:7656)在java.lang.Reflect.Method.Invoke（本机方法）在PID:22063 SIG:9

这里是我的user.java，错误的原因是：

package com.example.bauwagenapp;

import android.content.SharedPreferences;
import androidx.appcompat.app.AppCompatActivity;

public class User extends AppCompatActivity {

    private String name;
    private int guthaben;
    private int getrunken;

    public void setName(String name){
        this.name = name;
    }

    public String getName(){
        return name;
    }

    public void setGuthaben(int guthaben){
        this.guthaben = guthaben;
    }

    public int getGuthaben(){
        return guthaben;
    }

    public void setGetrunken(int getrunken){
        this.getrunken = getrunken;
    }

    public int getGetrunken(){
        return getrunken;
    }


    public User(String name){
        this.name = name;
        this.guthaben = getGuthabenFromPreference(this.name);
        this.getrunken = getGetrunkenFromPreference(this.name);
    }

    public int getGuthabenFromPreference(String name){
        SharedPreferences Guthaben_User = getApplicationContext().getSharedPreferences(name, 0);
        int Guthaben = Guthaben_User.getInt("Guthaben", 0);
        return Guthaben;
    }

    public int getGetrunkenFromPreference(String name){
        SharedPreferences Getrunken_User = getApplicationContext().getSharedPreferences(name, 0);
        int Getrunken = Getrunken_User.getInt("Getrunken", 0);
        return Getrunken;
    }
}

Answer 1

公共int getGetrunkenFromPreference（字符串名称）

不能调用从activity扩展的类中的公共函数，因为不能使用new运算符实例化该activity。