java - 将数据保存到Java Android中的全局变量

我正在尝试通过执行以下操作将数据保存到全局变量中：

public static String UnitCode;
public static String RDate;
public static String AArea;

    final EditText unitCode = (EditText) findViewById(R.id.editText1);
    final EditText reservationDate = (EditText) findViewById(R.id.editText2);
    final EditText Area = (EditText) findViewById(R.id.editText3);

            UnitCode = unitCode.getText().toString();
            RDate = reservationDate.getText().toString();
            AArea = Area.getText().toString();

这是在我的ReservationActivity.class内部。

但是，每当我在ReservationProcessActivity类上访问它时：

    UnitCode = ReservationActivity.UnitCode.toString();
    RDate = ReservationActivity.RDate.toString();
    Area = ReservationActivity.AArea.toString();

仅当我取消对ReservationProcessActivity中的零件的注释时，我的android应用程序才会突然崩溃，如果我对其进行注释，则可以正常工作。我做错了吗？

这是logcat错误：

02-06 11:50:10.956: E/AndroidRuntime(16482): FATAL EXCEPTION: main
02-06 11:50:10.956: E/AndroidRuntime(16482): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.appletest/com.example.appletest.ReservationProcessActivity}: java.lang.NullPointerException
02-06 11:50:10.956: E/AndroidRuntime(16482):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2308)
02-06 11:50:10.956: E/AndroidRuntime(16482):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2362)
02-06 11:50:10.956: E/AndroidRuntime(16482):    at android.app.ActivityThread.access$700(ActivityThread.java:168)
02-06 11:50:10.956: E/AndroidRuntime(16482):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1329)
02-06 11:50:10.956: E/AndroidRuntime(16482):    at android.os.Handler.dispatchMessage(Handler.java:99)
02-06 11:50:10.956: E/AndroidRuntime(16482):    at android.os.Looper.loop(Looper.java:137)
02-06 11:50:10.956: E/AndroidRuntime(16482):    at android.app.ActivityThread.main(ActivityThread.java:5493)
02-06 11:50:10.956: E/AndroidRuntime(16482):    at java.lang.reflect.Method.invokeNative(Native Method)
02-06 11:50:10.956: E/AndroidRuntime(16482):    at java.lang.reflect.Method.invoke(Method.java:525)
02-06 11:50:10.956: E/AndroidRuntime(16482):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1209)
02-06 11:50:10.956: E/AndroidRuntime(16482):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1025)
02-06 11:50:10.956: E/AndroidRuntime(16482):    at dalvik.system.NativeStart.main(Native Method)
02-06 11:50:10.956: E/AndroidRuntime(16482): Caused by: java.lang.NullPointerException
02-06 11:50:10.956: E/AndroidRuntime(16482):    at com.example.appletest.ReservationProcessActivity.onCreate(ReservationProcessActivity.java:102)
02-06 11:50:10.956: E/AndroidRuntime(16482):    at android.app.Activity.performCreate(Activity.java:5372)
02-06 11:50:10.956: E/AndroidRuntime(16482):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1104)
02-06 11:50:10.956: E/AndroidRuntime(16482):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2270)
02-06 11:50:10.956: E/AndroidRuntime(16482):    ... 11 more

这是我的ReservationProcessActivity类：

public class ReservationProcessActivity extends Activity {

    WebView webView;

    HttpResponse response;
    HttpClient httpclient;
    List<NameValuePair> nameValuePairs;
    StringBuffer buffer;
    HttpPost httppost;

    String UnitCode;
    String RDate;
    String Area;

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

        webView = (WebView)findViewById(R.id.webView1);
        webView.getSettings().setLoadWithOverviewMode(true);
        webView.getSettings().setUseWideViewPort(true);
        webView.setWebChromeClient(new WebChromeClient());
        webView.setWebViewClient(new MyBrowser());
        webView.getSettings().setBuiltInZoomControls(false);
        webView.getSettings().setJavaScriptEnabled(true);
        webView.setHorizontalScrollBarEnabled(false);

        UnitCode = ReservationActivity.UnitCode.toString();
        RDate = ReservationActivity.RDate.toString();
        Area = ReservationActivity.AArea.toString();


        webView.loadUrl("http://google.com/");

    }

}

ReservationActivity类：

package com.example.appletest;

import android.app.ActionBar;
import android.app.Activity;
import android.content.Intent;
import android.content.SharedPreferences;
import android.graphics.Color;
import android.graphics.drawable.ColorDrawable;
import android.os.Bundle;
import android.support.v4.app.NavUtils;
import android.text.Html;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.RadioButton;

public class ReservationActivity extends Activity {


    public static String UnitCode;
    public static String RDate;
    public static String AArea;

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

        //button
        final Button nextButton = (Button) findViewById(R.id.NextButton1);

        //textbox
        final EditText unitCode = (EditText) findViewById(R.id.editText1);
        final EditText reservationDate = (EditText) findViewById(R.id.editText2);
        final EditText Area = (EditText) findViewById(R.id.editText3);

        nextButton.setOnClickListener(new View.OnClickListener(){

            public void onClick(View v) {
                // TODO Auto-generated method stub

                UnitCode = unitCode.getText().toString();
                RDate = reservationDate.getText().toString();
                AArea = Area.getText().toString();

                Intent i = new Intent(ReservationActivity.this, ReservationProcessActivity.class);
                startActivity(i);
                finish();
            }

        });

}

最佳答案

如果ReservationProcessActivity在同一jvm中的ReservationActivity的onCreate之前调用了onCreate（），则ReservationActivity中的静态变量UnitCode仍然为null。当您从ReservationProcessActivity像这样使用它时：

UnitCode = ReservationActivity.UnitCode.toString();

那会导致您的崩溃。我不确定您活动中的事件顺序是什么，但是我认为这种情况正在发生。