点击按钮的Android计算器

我试图通过添加值txtA+txtB来计算名为lblAnswer的字段。我对安卓开发领域相当陌生，我想知道什么是最好的方法。我已经在GUI中添加了必要的编辑字段。我现在正在java文件中尝试并创建该方法。此方法已命名为doCalc。以下是我到目前为止的情况

public void doCalc() 
{
    lblAnswer = txtA + txtB;
}

有人建议我添加更多的代码，这里是完整的代码。谢谢你的建议

这是Java文件

      package com.example.wattsprofessional;

     import android.app.Activity;
     import android.os.Bundle;
     import android.view.Menu;

    public class MainActivity extends Activity {

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

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


public void doCalc() 
{
    lblAnswer = txtA + txtB;
    Double.parseDouble(txtA.getText().toString());
    lblAnswer.setText"t
}

这是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"
              tools:context=".MainActivity" >

    <EditText
           android:id="@+id/txtA"
           android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentTop="true"
             android:layout_centerHorizontal="true"
             android:layout_marginTop="40dp"
            android:ems="10"
            android:hint="Write Here"
            android:inputType="numberDecimal" >

    <requestFocus />
</EditText>

<EditText
    android:id="@+id/txtB"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignLeft="@+id/txtA"
    android:layout_below="@+id/txtA"
    android:layout_marginTop="32dp"
    android:ems="10"
    android:hint="Second Here"
    android:inputType="numberDecimal" />

<Button
    android:id="@+id/button1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_centerHorizontal="true"
    android:layout_centerVertical="true"
    android:text="@string/calculate" 
    android:onClick="doCalc"/>

<TextView
    android:id="@+id/lblAnswer"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@+id/button1"
    android:layout_centerHorizontal="true"
    android:layout_marginTop="50dp"
    android:text="TextView" />

    </RelativeLayout>

---

为了从

EditText

获取双精度值，您需要使用

Double.parseDouble（txtA.getText（）.toString（））

。要设置文本，可以使用

lblAnswer.setText（“文本”）

此外，从按钮调用它的最简单方法是在XML中设置它的

android:onClick

属性，例如

android:onClick=“doCalc”

编辑：您还需要创建对对象的引用。在onCreate（）之前，放置：

然后在onCreate（）中，需要初始化对象：

txtA = new (EditText)findViewById(R.Id.txtA);
txtB = new (EditText)findViewById(R.Id.txtB);
lblAnswer = new (TextView)findViewById(R.Id.lblAnswer);

---

您的代码缺少几个关键组件。检查您的代码，并检查我在下面准备的代码

package com.example.wattsprofessional;

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

public class MainActivity extends Activity {

    private EditText txtA, txtB;
    private Button button1;
// ^ we have declared these as fields up here so that we can access them throughout the page, past all the curly brackets

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

        txtA = (EditText) findViewById(R.id.txtA);
        txtB = (EditText) findViewById(R.id.txtB);
        button1 = (Button) findViewById(R.id.button1);
        // ^ this is where we initialize these. You did the xml correctly, but you still need to hook the java to it.
        // it allows us to use any names and locations we like not just same ones.
        // basically you say what it is (Button) and then use the following method to look for the id that you wrote in the xml

        initButton();
        // i made this listener so we'd have time. this is the oncreate method and is called instantly.
        // if we called doCalc here, we'd have no time to put numbers in.
    }

    private void initButton() {
        button1.setOnClickListener(new OnClickListener() {
            // this one performs an action when our button is clicked. it performs whatever is below
            @Override
            public void onClick(View v) {
                String strA = txtA.getText().toString();
                String strB = txtB.getText().toString();
                // we get our strings from our editexts. i think you know how to do this well.

                Double dblAnswer = doCalc(strA, strB);              
                // ^we pass them to our method, it does all the heavy lifting for us. and spits an answer for us.
                TextView lblAnswer = (TextView) findViewById(R.id.lblAnswer);
                // this is a local variable, as opposed to a field. i made so you know that you can do it like this - with the whole line here
                // the disadvantage is that we can't do anything to it outside of this curly bracket. but there are performs gains.
                // in general it's wasteful to use fields when you can suffice with local variable
                String answer = String.valueOf(dblAnswer);
                // we get our answer and turn it to a string.
                lblAnswer.setText(answer);
                // finally we set our result to the textView.
            }
        });
    }

    public double doCalc(String a, String b) {
        // a and b are both variables. they refer to the stuff we put in
        double dblA = Double.parseDouble(a);
        double dblB = Double.parseDouble(b);
        // we're gonna make both of these numbers so we can add them. right now they're just text.
        return dblA + dblB;
        // ^ this statement means that this method will spit a number out when it's done which we can use however.
    }

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

}

---

你到底有什么问题？据我们所知，一切进展顺利。我不能给你一个最好的方法，但我要做的是把我所有的计算都用不同的方法进行，这些方法取参数，然后返回一个值。谢谢你的快速回复。当我看到上面的实际方法时，lblAnswer=txtA+txtB；下面有一条错误线。它表示“无法解析为变量”。这是所有三个变量的错误消息。我不确定我把事情搞砸了。你需要将它们声明为全局变量，然后在

onCreate（）

中初始化它们。也许你最好提供更多的代码。正如Dare所说，您是否将这些值称为

ints

或

double

或您希望使用的任何格式？@Dare。请阅读并理解什么是全局变量。这不是你的建议，谢谢你。我现在就去试试这个。为了支持您在android上所说的：onClick。我在GUI中进行了这项工作，这是正确的位置吗？是的，

android:onClick

位于GUI的XML文件中。好的，所以我对上述建议有点困惑。我要做的是创建一个计算字段。txtA+txtB将是LBLANWER的计算字段？是。最简单的方法是创建变量来保存EditText中解析的值，然后将文本设置为

Double.toString（num1+num2）

（假设num1和num2是您的变量）。谢谢。我很抱歉，但我仍在学习，甚至这对我来说有点困惑。我已经在修订版中提供了我的完整代码。我将尝试完成此代码。但我仍然不太确定如何处理这个问题。我知道我应该做什么，但不知道如何做，如果这样做，因为。谢谢你到目前为止最好的答复。我同意我有很多教程需要复习。这些细节帮助很大。

package com.example.wattsprofessional;

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

public class MainActivity extends Activity {

    private EditText txtA, txtB;
    private Button button1;
// ^ we have declared these as fields up here so that we can access them throughout the page, past all the curly brackets

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

        txtA = (EditText) findViewById(R.id.txtA);
        txtB = (EditText) findViewById(R.id.txtB);
        button1 = (Button) findViewById(R.id.button1);
        // ^ this is where we initialize these. You did the xml correctly, but you still need to hook the java to it.
        // it allows us to use any names and locations we like not just same ones.
        // basically you say what it is (Button) and then use the following method to look for the id that you wrote in the xml

        initButton();
        // i made this listener so we'd have time. this is the oncreate method and is called instantly.
        // if we called doCalc here, we'd have no time to put numbers in.
    }

    private void initButton() {
        button1.setOnClickListener(new OnClickListener() {
            // this one performs an action when our button is clicked. it performs whatever is below
            @Override
            public void onClick(View v) {
                String strA = txtA.getText().toString();
                String strB = txtB.getText().toString();
                // we get our strings from our editexts. i think you know how to do this well.

                Double dblAnswer = doCalc(strA, strB);              
                // ^we pass them to our method, it does all the heavy lifting for us. and spits an answer for us.
                TextView lblAnswer = (TextView) findViewById(R.id.lblAnswer);
                // this is a local variable, as opposed to a field. i made so you know that you can do it like this - with the whole line here
                // the disadvantage is that we can't do anything to it outside of this curly bracket. but there are performs gains.
                // in general it's wasteful to use fields when you can suffice with local variable
                String answer = String.valueOf(dblAnswer);
                // we get our answer and turn it to a string.
                lblAnswer.setText(answer);
                // finally we set our result to the textView.
            }
        });
    }

    public double doCalc(String a, String b) {
        // a and b are both variables. they refer to the stuff we put in
        double dblA = Double.parseDouble(a);
        double dblB = Double.parseDouble(b);
        // we're gonna make both of these numbers so we can add them. right now they're just text.
        return dblA + dblB;
        // ^ this statement means that this method will spit a number out when it's done which we can use however.
    }

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

}