Android共享首选项崩溃

当我将它放入手机进行调试时，此活动崩溃，我只是添加了存储变量的部分 . 我做错什么了吗？

它是一个活动，如果他们之前设置了它们，它们应该获得当前变量，用户也可以设置它们 .

package com.software.roux.diabcalc;

import android.content.Intent;
import android.content.SharedPreferences;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.PrintWriter;

import static com.software.roux.diabcalc.R.id.bolus;

public class Settings extends AppCompatActivity {

    SharedPreferences mPrefs = getSharedPreferences("label", 0);

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_settings);
        setTitle("Insulin Calculator by Ben Roux");

        String bolusString = mPrefs.getString("bolus", "0");
        String corrString = mPrefs.getString("correction", "0");
        String lowString = mPrefs.getString("low", "0");
        String highString = mPrefs.getString("high", "0");

        EditText b1 = (EditText)findViewById(R.id.bolus);
        b1.setText(bolusString);

        EditText b2 = (EditText)findViewById(R.id.correction);
        b2.setText(corrString);

        EditText b3 = (EditText)findViewById(R.id.targetlow);
        b3.setText(lowString);

        EditText b4 = (EditText)findViewById(R.id.targethigh);
        b4.setText(highString);
    }

    public void switchclick(View a) {
        if (a.getId() == R.id.backbutton) {
            Intent myIntent = new Intent(Settings.this, MainActivity.class);
            Settings.this.startActivity(myIntent);
        }
    }

    public void setclick(View b) {
        if (b.getId() == R.id.setter) {

            EditText b1 = (EditText)findViewById(R.id.bolus);
            String bolussave = ""+b1;
            SharedPreferences.Editor mEditor1 = mPrefs.edit();
            mEditor1.putString("bolus", bolussave).commit();

            EditText b2 = (EditText)findViewById(R.id.correction);
            String corrsave = ""+b2;
            SharedPreferences.Editor mEditor2 = mPrefs.edit();
            mEditor2.putString("correction", corrsave).commit();


            EditText b3 = (EditText)findViewById(R.id.targetlow);
            String lowsave = ""+b3;
            SharedPreferences.Editor mEditor3 = mPrefs.edit();
            mEditor3.putString("low", lowsave).commit();


            EditText b4 = (EditText)findViewById(R.id.targethigh);
            String highsave = ""+b4;
            SharedPreferences.Editor mEditor4 = mPrefs.edit();
            mEditor4.putString("high", highsave).commit();


        }
    }
}

更新崩溃日志：

03-18 15：29：59.477 7801-7801 / com.software.roux.diabcalc E / AndroidRuntime：FATAL EXCEPTION：main进程：com.software.roux.diabcalc，PID：7801 java.lang.RuntimeException：无法实例化activity ComponentInfo {com.software.roux.diabcalc / com.software.roux.diabcalc.Settings}：java.lang.NullPointerException：尝试调用虚方法'android.content.SharedPreferences android.content.Context.getSharedPreferences（java.lang） .string，int）'在android.app.ActivityThread.perleLaunchActivity（ActivityThread.java：30：94）上的空对象引用，位于android.app.ActivityThread.access $ 1100的android.app.ActivityThread.handleLaunchActivity（ActivityThread.java:3350） （ActivityThread.java:222）在android.app.A.运行时，Android.O.Roper.loop（Looper . ）上的android.app.ActivityThread $ H.handleMessage（ActivityThread.java:1795）位于android.os.Handler.dispatchMessage（Handler.java:102） . java：158）在android.app.ActivityThread.main（ActivityThread.java:7229）的java.lang.reflect.Method.invoke（Native Method）com.android.in com.android.internal.os.ZygoteInit.main（ZygoteInit.java:1120）中的ternal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:1230）引起：java.lang.NullPointerException：尝试调用虚方法' android.content.SharedPreferences android.content.Context.getSharedPreferences（java.lang.String，int）'在com.software.roux.diabcalc上的android.content.ContextWrapper.getSharedPreferences（ContextWrapper.java:185）上的空对象引用上.Settings . （Settings.java:21）在android.app.ActivityThread.performLaunchActivity（ActivityThread.java）的android.app.Instrumentation.newActivity（Instrumentation.java:1095）的java.lang.Class.newInstance（Native Method）中 . 3084）在Android.app.A活动时，我在Android.app.ActivityThread.access $ 1100（ActivityThread.java:222）的android.app.ActivityThread.handleLaunchActivity（ActivityThread.java:3350）.ActivityThread $ H.handleMessage（ActivityThread.java:1795）在Android.app.Handler.dispatchMessage（Handler.java:102）android.app.Looper.loop（Looper.java:158）android.app .ActivityThread.main（ActivityThread.java:7229）位于com.android的com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:1230）的java.lang.reflect.Method.invoke（Native Method） .internal.os.ZygoteInit.main（ZygoteInit.java:1120）