java - 我在多个 View 中需要相同的变量，但它不起作用

Question

我正在尝试创建一个计算行星重量的应用程序。在第一个 View 中，用户输入他们的体重并且它有一个输入按钮，在第二个 View 中是一个单选按钮列表和选择按钮。我想让它把它们的重量乘以地球的力。为此，我需要 activity_main.xml 和 planets.xml 的权重变量。起初我只在 planets 中使用它，但现在它也在 main 中，if else 语句出错。

activity_main.xml:

<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" >

<TextView
    android:id="@+id/askwtTextView"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentLeft="true"
    android:layout_alignParentTop="true"
    android:layout_marginLeft="17dp"
    android:layout_marginTop="19dp"
    android:text="@string/askwt" />

<EditText
    android:id="@+id/inputwtEditText"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignLeft="@+id/askwtTextView"
    android:layout_below="@+id/askwtTextView"
    android:layout_marginTop="26dp"
    android:ems="10"
    android:inputType="numberDecimal" />

<Button
    android:id="@+id/enterButton"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignLeft="@+id/inputwtEditText"
    android:layout_below="@+id/inputwtEditText"
    android:layout_marginTop="38dp"
    android:onClick="buttonclick"
    android:text="@string/enter" />

</RelativeLayout>

行星.xml:

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

<TextView
    android:id="@+id/planetTextView"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/planet" />

<TextView
    android:id="@+id/textViewform2"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="" />

<RadioGroup
    android:id="@+id/radioGroup1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content" >

    <RadioButton
        android:id="@+id/mercuryRadio"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:checked="true"
        android:text="@string/mercury" />

    <RadioButton
        android:id="@+id/venusRadio"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/venus" />

    <RadioButton
        android:id="@+id/earthRadio"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/earth" />

    <RadioButton
        android:id="@+id/marsRadio"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:checked="true"
        android:text="@string/mars" />

    <RadioButton
        android:id="@+id/jupiterRadio"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/jupiter" />

    <RadioButton
        android:id="@+id/saturnRadio"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/saturn" />

    <RadioButton
        android:id="@+id/uranusRadio"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:checked="true"
        android:text="@string/uranus" />

    <RadioButton
        android:id="@+id/neptuneRadio"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/neptune" />

    <RadioButton
        android:id="@+id/plutoRadio"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/pluto" />
</RadioGroup>


<Button
    android:id="@+id/selectButton"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:onClick="buttonclick2"
    android:text="@string/select" />

<TextView
    android:id="@+id/textViewform2"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
     />

</LinearLayout>

Java:

package com.deitel.planetaryweight;

import android.os.Bundle;
import android.app.Activity;
import android.widget.*;
import android.view.View;
import android.view.Menu;
import android.widget.Button;
import android.widget.RadioButton;
import android.widget.RadioGroup;
import android.widget.EditText;
import android.widget.TextView;
import java.text.DecimalFormat;

public class MainActivity extends Activity {

//Global variable
double weight;
private Button enter;  // creates a button 


@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    enter = (Button) findViewById(R.id.enterButton);

    //Start with first screen
    setContentView(R.layout.activity_main);
}

//buttonclick for form 1
public void buttonclick(View view){



    //creates an editext and assigns the resource id of the xml edittext.
    EditText wtentry = (EditText)findViewById(R.id.inputwtEditText);

    //Receives the input from the edittext, converts it to a double (number).
    weight = Double.parseDouble(wtentry.getText().toString());


      //switch views to screen 2
       setContentView(R.layout.planets);

       //change the value of the textview on screen 2 to the calculation value
       TextView t2 = (TextView)findViewById(R.id.textViewform2);
       t2.setText(Double.toString(weight));

        }

        //buttonclick for form 2!
        public void buttonclick2(View view){
            setContentView(R.layout.planets);

            RadioButton mercury = (RadioButton) findViewById(R.id.mercuryRadio);
            RadioButton venus = (RadioButton) findViewById(R.id.venusRadio);
            RadioButton earth = (RadioButton) findViewById(R.id.earthRadio);            
            RadioButton mars = (RadioButton) findViewById(R.id.marsRadio);
            RadioButton jupiter = (RadioButton) findViewById(R.id.jupiterRadio);
            RadioButton saturn = (RadioButton) findViewById(R.id.saturnRadio);
            RadioButton uranus = (RadioButton) findViewById(R.id.uranusRadio);
            RadioButton neptune = (RadioButton) findViewById(R.id.neptuneRadio);
            RadioButton pluto = (RadioButton) findViewById(R.id.plutoRadio);

            //Makes a variable for the entered amount
            Double mercurypf;
            Double venuspf;
            Double earthpf;
            Double marspf;
            Double jupiterpf;
            Double saturnpf;
            Double uranuspf;
            Double neptunepf;
            Double plutopf;
            Double weight;

            // constants
            final double mercuryforce = 0.38; 
            final double venusforce = 0.91; 
            final double earthforce = 1.00; 
            final double marsforce = 0.38; 
            final double jupiterforce = 2.34; 
            final double saturnforce = 1.06; 
            final double uranusforce = .92;
            final double neptuneforce = 1.19;
            final double plutoforce = 0.06;



            // Code used to determine which planet RadioButton is checked:

            if(mercury.isChecked())
            {
                mercurypf = mercuryforce * weight;
            }
            else
            {
                mercurypf = 0.00;
            }


            if(venus.isChecked())
            {
                venuspf = venusforce * weight;
            }
            else
            {
                venuspf = 0.00;

            }
            if(earth.isChecked())
            {
                earthpf = earthforce * weight;
            }
            else
            {
                earthpf = 0.00;
            }
            if(mars.isChecked())
            {
                marspf = marsforce * weight;
            }
            else
            {
                marspf = 0.00;
            }
            if(jupiter.isChecked())
            {
                jupiterpf =jupiterforce * weight;
            }
            else
            {
                jupiterpf = 0.00;
            }
            if(saturn.isChecked())
            {
                saturnpf = saturnforce * weight;
            }
            else
            {
                saturnpf = 0.00;
            }

            if(uranus.isChecked())
            {
                uranuspf = uranusforce * weight;
            }
            else
            {
                uranuspf = 0.00;
            }

            if(neptune.isChecked())
            {
                neptunepf = neptuneforce * weight;
            }
            else
            {
                neptunepf = 0.00;
            }

            if(pluto.isChecked())
            {
                plutopf = plutoforce * weight;
            }
            else
            {
                plutopf = 0.00;
            }

        }
    }

Answer 1

一种方法是:

创建一个名为 say Constants 的新类，并在其中将此变量声明为静态变量。现在您可以从所有 Activity 中访问此变量。

public class Constants {
     public static double weight;
}

从您的所有 Activity 中访问它

Constants.weight = 2.5;