我需要在多个视图中使用相同的变量，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。在第一个视图中，用户输入他们的体重，它有一个输入按钮，在第二个视图中是一个单选按钮列表和选择按钮。我想让它们的重量乘以地球的力量。为此，我需要activity_main.xml 和planets.xml 的权重变量。起初我只在行星上使用它，但现在它也在 main 中，if else 语句出错了。

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>

planets.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，并将该变量声明为静态变量。现在您可以从所有活动中访问此变量。

public class Constants {
     public static double weight;
}

从您的所有活动中访问它

Constants.weight = 2.5;

Answer 2

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

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

您应该在找到任何视图之前设置内容视图。

此外，您不需要对定义变量的方式进行任何更改，因为 weight 是 MainActivity 类中的私有变量，并且您正在同一活动中转换视图。该变量在您更改视图之前存储了 editText 的值，因此即使您更改了 contentView，它也不会丢失同一类中的值。据我所知，问题在于您没有正确设置enter 按钮（我上面建议的更改应该有效）。

Answer 3

除此之外，您还需要解决一些结构和设计问题。查看文档以获取有关在活动之间来回传递信息的信息。 setContentView() 不应在 Activity 中多次调用，除非您有充分的理由这样做。

public class MainActivity extends Activity {
    /* You should get used to declaring everything with the correct visibility.  Good practice is to make everything private and use public mutator methods */
    //Global variable
    private double weight;
    private Button enter;  // creates a button 

    // Views
    private EditText wtEntry;
    private TextView txtForm2;

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

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

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

        //creates an editext and assigns the resource id of the xml edittext.
        wtEntry = (EditText)findViewById(R.id.inputwtEditText);
        txtForm2 = (TextView)findViewById(R.id.textViewform2);
    }
    // Button clicks shouldn't do anything but perform clicky actions. Leave field initialization, view creation, etc to the Activity.
    //buttonclick for form 1
    public void buttonclick(View view){
        //Receives the input from the edittext, converts it to a double (number).
        weight = Double.parseDouble(wtEntry.getText().toString());

        //change the value of the textview on screen 2 to the calculation value
       t2.setText(Double.toString(weight));

       // If you want a new layout, it's best to start a new activity.
       // It looks like you want to get information back, so use startActivityForResult().
       // setContentView(R.layout.planets);
       Intent dataIntent = new Intent(this, PlanetChooser.class);
       dataIntent.putExtra("com.yourpackage.identifier.DATA_WEIGHT", weight);
       startActivityForResult(dataIntent, Activity.RESULT_OK);
    }
    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);

        // Check that the resultCode is the same as we started the activity with
        if(resultCode == Activity.RESULT_OK){
            // get the double from the Intent, using the same string name (package prefixed)
            // or a default value if it didn't get set.
            double resultWeight = data.getDoubleExtra("com.yourpackage.identifier.RESULT_WEIGHT", 0.0);

            // Now do something with resultWeight
        }
    }
}
// PlanetChooser.class
public class PlanetChooser extends Activity {
    // constants, usually denoted by uppercase and declared static and final
    public static final double MERCURYFORCE = 0.38; 
    public static final double VENUSFORCE = 0.91; 
    public static final double EARTHFORCE = 1.00; 
    public static final double MARSFORCE = 0.38; 
    public static final double JUPITERFORCE = 2.34; 
    public static final double SATURNFORCE = 1.06; 
    public static final double URANUSFORCE = 0.92;
    public static final double NEPTUNEFORCE = 1.19;
    public static final double PLUTOFORCE = 0.06;

    private RadioButton mercury, venus, earth, mars, jupiter, saturn, uranus, neptune, pluto;

    // No need to use the Double object as opposed to the primitive unless you have good reason
    private double mercurypf, venuspf, earthpf, marspf, jupiterpf, saturnpf, uranuspf, neptunepf, plutopf, weight;

    // One variable will suffice, it seems.
    private double resultForce;

    public void onCreate(Bundle s){
        super.onCreate(s);
        setContentView(R.layout.planets);

        mercury = (RadioButton) findViewById(R.id.mercuryRadio);
        venus = (RadioButton) findViewById(R.id.venusRadio);
        earth = (RadioButton) findViewById(R.id.earthRadio);            
        mars = (RadioButton) findViewById(R.id.marsRadio);
        jupiter = (RadioButton) findViewById(R.id.jupiterRadio);
        saturn = (RadioButton) findViewById(R.id.saturnRadio);
        uranus = (RadioButton) findViewById(R.id.uranusRadio);
        neptune = (RadioButton) findViewById(R.id.neptuneRadio);
        pluto = (RadioButton) findViewById(R.id.plutoRadio);
    }
    public void buttonclick2(View view){
        /*
        It looks to me here you're looking to see which box is checked, and set a value based on 
        that planet.  Since instance variables (in this case mercurypf, jupiterpf, etc) are initialized
        to the default value (0), there's no need to set them manually.
        */

        // Code used to determine which planet RadioButton is checked:
        if(mercury.isChecked())    {
            resultForce = MERCURYFORCE * weight;
        }
        if(venus.isChecked()){
            resultForce = VENUSFORCE * weight;
        }
        if(earth.isChecked()){
            resultForce = EARTHFORCE * weight;
        }
        if(mars.isChecked()){
            resultForce = MARSFORCE * weight;
        }
        if(jupiter.isChecked()){
            resultForce =JUPITERFORCE * weight;
        }
        if(saturn.isChecked()){
            resultForce = SATURNFORCE * weight;
        }
        if(uranus.isChecked()){
            resultForce = URANUSFORCE * weight;
        }
        if(neptune.isChecked()){
            resultForce = NEPTUNEFORCE * weight;
        }
        if(pluto.isChecked()){
            resultForce = PLUTOFORCE * weight;
        }
        // Create a new data Intent to pass back to the calling activity, set the result code, 
        // and manually finish() this activity.
        Intent dataIntent = new Intent(this);
        dataIntent.putDoubleExtra("com.yourpackage.identifier.RESULT_DATA", resultForce);
        setResult(Activity.RESULT_OK, dataIntent);
        finish();
    }
}

Answer 4

使用应用程序或静态变量全局保存值。看例子

创建一个扩展 Application 的新类。

public class Globals extends Application{
  private int data=200;

  public int getData(){
  return this.data;
}

 public void setData(int d){
  this.data=d;
 }

}

Second:

Add the class to the AndroidManifest file as an attribute of <application> tag:

 <application android:name=".Globals" />

Then you can access your global data from any Activity by calling getApplication()

Globals g = (Globals)getApplication();
int data=g.getData();

静态变量示例

class Global{
    public static int global=1;
}

in your activity simply use it with its class name

 int a;
 a=Global.global;