Question

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。我做错了吗？

这是一个活动，如果他们之前设置了它们，它们应该获取当前变量，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：致命异常：主要处理：com.software.roux.diabcalc，PID：7801 java.lang.RuntimeException：无法实例化活动 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null对象引用上在 android.app.ActivityThread.performLaunchActivity（ActivityThread.java:3094）在 android.app.ActivityThread.handleLaunchActivity（ActivityThread.java:3350）在android.app.ActivityThread.access $ 1100（ActivityThread.java:222）在 android.app.ActivityThread $ H.handleMessage（ActivityThread.java:1795）在android.os.Handler.dispatchMessage（Handler.java:102）在android.os.Looper.loop（Looper.java:158）在android.app.ActivityThread.main（ActivityThread.java:7229） at java.lang.reflect.Method.invoke（Native Method）在 com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:1230）在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:1120）引起：java.lang.NullPointerException：尝试调用虚拟方法'android.content.SharedPreferences android.content.Context.getSharedPreferences（java.lang.String，int）' 在null对象引用上在 android.content.ContextWrapper.getSharedPreferences（ContextWrapper.java:185）在com.software.roux.diabcalc.Settings。（Settings.java:21） at java.lang.Class.newInstance（Native Method）在android.app.Instrumentation.newActivity（Instrumentation.java:1095）在 android.app.ActivityThread.performLaunchActivity（ActivityThread.java:3084）在 android.app.ActivityThread.handleLaunchActivity（ActivityThread.java:3350）在android.app.ActivityThread.access $ 1100（ActivityThread.java:222）在 android.app.ActivityThread $ H.handleMessage（ActivityThread.java:1795）在android.os.Handler.dispatchMessage（Handler.java:102）在android.os.Looper.loop（Looper.java:158）在android.app.ActivityThread.main（ActivityThread.java:7229） at java.lang.reflect.Method.invoke（Native Method）在 com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:1230）在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:1120）

Answer 1

稍后启动SharedPreferences mPrefs。在onCreate方法中。

仅在context方法之后初始化onCreate。所以，这必须工作：

SharedPreferences mPrefs;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_settings);
        setTitle("Insulin Calculator by Ben Roux");
 mPrefs= getSharedPreferences("label", 0);

另一个问题是，在当前代码中，您只需将EditText变量的地址保存在内存中。要检索文本，请使用：

String bolussave = ""+b1.getText().toString();

Answer 2

尝试在OnCreate方法中实例化mPref。

@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");
    mPrefs = getSharedPreferences("label", 0);
    ...
    ...

Android共享首选项崩溃

2 个答案: