如何在Java中跨多个类使用变量？

Question

I am trying to create my first app in android studio, on the main screen there are three tick boxes asking the user which number of sides they want on the dice. I have a variable called sides which is set to 6,8 or 12 depending on which tick box the user ticks. I want the variable "sides" on the second activity so it can be used to generate a random integer between one and whatever "sides" is set to.

Answer 1

In first activity Lets assume that you have button GO . When You clicks on Button GO it should start Second Activity say Activity2. Add following code to onClick of GO Button

Intent act2=new Intent(this,Activity2.class);//"this" is  activity reference
act2.putExtra("key",value);
startActivity(act2);

Now in the onCreate method of Activity2 you can retrieve value of key as follows:

Int key=getIntent().getIntExtra("key",0);//0 is default value

In the same way as done above you can pass value of "side" variable to next activity

Answer 2

You can also save it in the Internal Storage and load it when you need, it is very useful because that way you can load it in every activity and every class you want.

you can learn how here . I recommend watching all three parts.

Answer 3

you can use SharedPreferences,

To obtain shared preferences, use the following method In your activity:

SharedPreferences prefs = this.getSharedPreferences(
  "com.example.app", Context.MODE_PRIVATE);

To read preferences:

String dateTimeKey = "com.example.app.datetime";

// use a default value using new Date()
long l = prefs.getLong(dateTimeKey, new Date().getTime()); 

To edit and save preferences

Date dt = getSomeDate();
prefs.edit().putLong(dateTimeKey, dt.getTime()).apply();

The android sdk's sample directory contains an example of retrieving and storing shared preferences. Its located in the:

<android-sdk-home>/samples/android-<platformversion>/ApiDemos directory

Answer 4

Easiest way is to use singleton classes.

public class DataHolder {


public int sides  = 0;

    private static DataHolder dataHolder = new DataHolder();

    public static DataHolder getInstance()
    {
        return dataHolder;
    }


} 

DataHolder.getInstance().sides=sideInActivityA;

you can access the variable by using int sideInActivityB = DataHolder.getInstance().sides;

Answer 5

This can be done by static global variables or the public variables which can be accessed by inheriting the class. However importing the global static classes does the same.