Android 空指针异常

我想构建一个应用程序，从ListView中的EditText获取输入。 基本上，我有三列，每列都有EditText。现在，当我试图从用户那里获取输入并将其存储在String类型的变量中，当我运行这个应用程序时，它会崩溃，因为它得到NullPointerException

这是我的MainActivity.java

package com.example.manuj.autocalc;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.text.Editable;
import android.text.TextWatcher;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.TextView;

import java.util.ArrayList;

public class MainActivity extends AppCompatActivity {

    EditText editTotal;
    EditText editItem;
    EditText editAmt;
    String item;
    String amt;
    String total;
    ListView listView;
    CustomAdapter customAdapter;

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

        editItem=findViewById(R.id.itemEdit);
        editTotal=findViewById(R.id.editTotal);
        editAmt=findViewById(R.id.amtEdit);

        item=editItem.getText().toString();
        total=editTotal.getText().toString();
        amt=editAmt.getText().toString();

        final ArrayList<Calc> calcs=new ArrayList<>();
        calcs.add(new Calc("    -","    -","     -"));
        calcs.add(new Calc("    -","    -","     -"));
        calcs.add(new Calc("    -","    -","     -"));
        calcs.add(new Calc("    -","    -","     -"));
        calcs.add(new Calc("    -","    -","     -"));

        listView=findViewById(R.id.listView);
        customAdapter=new CustomAdapter(this,-1,calcs);
        listView.setAdapter(customAdapter);
//        Calc calc=new Calc(item,amt,total);
//        calcs.add(calc);
        customAdapter.notifyDataSetChanged();







    }
}

这是我的错误

E/AndroidRuntime: FATAL EXCEPTION: main
              Process: com.example.manuj.autocalc, PID: 6618
              java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.manuj.autocalc/com.example.manuj.autocalc.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.text.Editable android.widget.EditText.getText()' on a null object reference
                  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2984)
                  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3045)
                  at android.app.ActivityThread.-wrap14(ActivityThread.java)
                  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1642)
                  at android.os.Handler.dispatchMessage(Handler.java:102)
                  at android.os.Looper.loop(Looper.java:154)
                  at android.app.ActivityThread.main(ActivityThread.java:6776)
                  at java.lang.reflect.Method.invoke(Native Method)
                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1518)
                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1408)
               Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.text.Editable android.widget.EditText.getText()' on a null object reference
                  at com.example.manuj.autocalc.MainActivity.onCreate(MainActivity.java:36)
                  at android.app.Activity.performCreate(Activity.java:6956)
                  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1126)
                  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2927)
                  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3045) 
                  at android.app.ActivityThread.-wrap14(ActivityThread.java) 
                  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1642) 
                  at android.os.Handler.dispatchMessage(Handler.java:102) 
                  at android.os.Looper.loop(Looper.java:154) 
                  at android.app.ActivityThread.main(ActivityThread.java:6776) 
                  at java.lang.reflect.Method.invoke(Native Method) 
                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1518) 
                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1408) 

---

应用程序已终止。

加载活动时，您正在从EditText读取文本，然后添加了.toString（）。首先.getText（）返回Null，然后将Null转换为字符串。因此崩溃

为了避免这次事故

只要打个空支票就行了

if(your_edit_text.getText() != null)
 {
   //Then do your operation
 }

---

看起来像itemEdit、editTotal、amtEdit属于您的列表\u item.xml布局而不是活动\u main.xml。您已经在MainActivity类中初始化了这三个EditText，这可能是它抛出错误的原因。但无论如何，请提供您的xml布局。

发布我编辑的崩溃日志，原因是：java.lang.NullPointerException:尝试在com.example.manuj.autocalc.MainActivity.onCreate（MainActivity.java:36）上的空对象引用上调用虚拟方法“android.text.Editable android.widget.EditText.getText（）”看起来

R.id.itemEdit

不属于布局

R.layout.activity\u main

您不能这样做。你需要在适配器中处理列表项的写入，然后我还能做什么。请帮助我是初学者。堆栈跟踪声明它是在null对象上调用的getText。请放入你的xml。如果有帮助，请查看此链接：我已添加了xml文件。请检查。是的，你是对的。但是我能够显示列表项。但是我想要它需要在MainActivity中显示，因此当我获取输入时，它会崩溃，当我只想显示没有获取输入代码的列表项时，它就会显示。您的主要目标是什么？比如你为什么要使用ListView？因为我想构建一个list notes应用程序。所以我认为它需要一个ListView，因为用户将添加list ITME。在activity_main.xml中创建另一个editbox。从那里获取输入。

E/AndroidRuntime: FATAL EXCEPTION: main
              Process: com.example.manuj.autocalc, PID: 6618
              java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.manuj.autocalc/com.example.manuj.autocalc.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.text.Editable android.widget.EditText.getText()' on a null object reference
                  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2984)
                  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3045)
                  at android.app.ActivityThread.-wrap14(ActivityThread.java)
                  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1642)
                  at android.os.Handler.dispatchMessage(Handler.java:102)
                  at android.os.Looper.loop(Looper.java:154)
                  at android.app.ActivityThread.main(ActivityThread.java:6776)
                  at java.lang.reflect.Method.invoke(Native Method)
                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1518)
                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1408)
               Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.text.Editable android.widget.EditText.getText()' on a null object reference
                  at com.example.manuj.autocalc.MainActivity.onCreate(MainActivity.java:36)
                  at android.app.Activity.performCreate(Activity.java:6956)
                  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1126)
                  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2927)
                  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3045) 
                  at android.app.ActivityThread.-wrap14(ActivityThread.java) 
                  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1642) 
                  at android.os.Handler.dispatchMessage(Handler.java:102) 
                  at android.os.Looper.loop(Looper.java:154) 
                  at android.app.ActivityThread.main(ActivityThread.java:6776) 
                  at java.lang.reflect.Method.invoke(Native Method) 
                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1518) 
                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1408) 

if(your_edit_text.getText() != null)
 {
   //Then do your operation
 }