将两个数字添加到Android Studio，如此简单的项目，但会出错

Question

我添加2个数字，然后单击按钮-应用程序不断停止，并且此错误显示在Android Studio中--- java.lang.NullPointerException：尝试调用虚拟方法'android.text.Editable android.widget.EditText .getText（）'（在空对象引用上）

我该如何解决？

这是activity_main.xml文件

<?xml version="1.0" encoding="utf-8"?>
    <LinearLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        xmlns:tools="http://schemas.android.com/tools"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical"
        tools:context=".MainActivity">


        <Button
            android:id="@+id/btnAdd"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginBottom="250dp"
            android:text="Add"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.262"
            app:layout_constraintStart_toStartOf="parent" />

        <EditText
            android:id="@+id/etNum1"
            android:layout_width="250dp"
            android:layout_height="wrap_content"
            android:ems="10"
            android:inputType="number"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            tools:layout_editor_absoluteY="112dp" />

        <EditText
            android:id="@+id/etNum2"
            android:layout_width="250dp"
            android:layout_height="wrap_content"
            android:ems="10"
            android:inputType="number"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            tools:layout_editor_absoluteY="267dp" />

        <TextView
            android:id="@+id/txtAnswer"
            android:layout_width="250dp"
            android:layout_height="wrap_content"
            android:text="Answer:"
            android:textSize="32dp"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.895"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

    </LinearLayout>

这是MainActivity.java文件

package com.naila.triangle;

import androidx.appcompat.app.AppCompatActivity;

import android.annotation.SuppressLint;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

    EditText num1;
    EditText num2;
    Button add;
    TextView result;

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

        num1= (EditText) findViewById(R.id.etNum1);
        num1= (EditText) findViewById(R.id.etNum2);
        add= (Button) findViewById(R.id.btnAdd);
        result= (TextView) findViewById(R.id.txtAnswer);

        add.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                int number1 = Integer.parseInt(num1.getText().toString());
                int number2 = Integer.parseInt(num2.getText().toString());
                int sum = number1 + number2;
                result.setText("Answer: "+ sum);

            }
        });




    }
}

Answer 1

您两次初始化num1。将num1 = ...更改为num2 = ...。