Question

我是应用程序制作的新手，正在制作一个简单的计算器。

每当我点击一个按钮时，我都会收到消息“不幸的是，计算器已停止”。任何帮助将不胜感激。

XML文件：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".Calculator" >

<EditText
    android:id="@+id/editText1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentLeft="true"
    android:layout_alignParentTop="true"
    android:layout_marginLeft="70dp"
    android:layout_marginTop="25dp"
    android:ems="10" >

    <requestFocus />
</EditText>

<EditText
    android:id="@+id/editText2"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@+id/editText1"
    android:layout_marginLeft="70dp"
    android:layout_marginTop="26dp"
    android:ems="10" />

<Button
    android:id="@+id/button1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentLeft="true"
    android:layout_centerVertical="true"
    android:layout_marginLeft="20dp"
    android:text="Add"
    android:onClick="DoAdd" />

<Button
    android:id="@+id/button2"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentLeft="true"
    android:layout_centerVertical="true"
    android:layout_marginLeft="90dp"
    android:text="Subtract" 
    android:onClick="DoMinus"/>

<Button
    android:id="@+id/button3"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:layout_alignParentRight="true"
    android:layout_centerVertical="true"
    android:layout_toRightOf="@+id/button2"
    android:onClick="DoTimes"
    android:text="Multiply" />

<TextView
    android:id="@+id/textView1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@+id/button2"
    android:layout_centerHorizontal="true"
    android:layout_marginTop="94dp"
    android:text="TextView" />

Java文件：

package com.example.calculator;

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;

public class Calculator extends Activity {

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

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.calculator, menu);
    return true;
}

public void doAdd(View v)
{
    EditText firstNumber = (EditText)findViewById(R.id.editText1);
    EditText secondNumber = (EditText)findViewById(R.id.editText2);

    double x = Double.parseDouble(firstNumber.getText().toString());
    double y = Double.parseDouble(secondNumber.getText().toString());

    double total = x + y;

    TextView answerSpace = (TextView)findViewById(R.id.textView1);
    answerSpace.setText(Double.toString(total));
}
}

三江源。

Answer 1

将xml onClick属性更改为与java代码中的方法名称完全匹配：

<Button
android:id="@+id/button1"
...
android:onClick="doAdd" />

注意开头的小写d。

如果这两个不匹配，Android会尝试调用您指定的onClick方法时应用程序崩溃。

Answer 2

FD_ already pointed out the mistake from your code.

But for better coding approach you can follow this. If you wish.

In your xml file, define single method name for onClick on each button ie for
addition,substration,division,multiplication.

What i mean to say...?

// For Addition....

<Button
  android:id="@+id/button1"
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:layout_alignParentLeft="true"
  android:layout_centerVertical="true"
  android:layout_marginLeft="20dp"
  android:text="Add"
  android:onClick="calculate" />

 //Define android:onClick="calculate" for remaining 3 buttons

 ie say for subtraction 

 <Button
  android:id="@+id/button1"
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:layout_alignParentLeft="true"
  android:layout_centerVertical="true"
  android:layout_marginLeft="20dp"
  android:text="Subract"
  android:onClick="calculate" /> 

 do similarly for division and multiplication


 Now, in Java File

 1)Define Variables globally
 2)Find their ids in onCreateMethod(), ie when the activity created.

 How to do this?


 public class Calculator extends Activity
 {
  EditText firstNumber,secondNumber;

    onCreate()
   {
     firstNumber = (EditText)findViewById(R.id.editText1);
     secondNumber = (EditText)findViewById(R.id.editText2);
   }

   public void calculate(View v)
   {

    switch(v.getId())
      {

         case R.id.button1:
              // Do coding here addition....
              break;
          case R.id.button2:
              // Do coding here substraction....
              break;
          case R.id.button3:
              // Do coding here multiplication....
              break;
          case R.id.button4:
              // Do coding here division....
              break;

      }
   }


 }

当我按下我制作的应用程序上的按钮时，该应用程序关闭，但不幸的是该应用程序已关闭

2 个答案: