Android-全局变量？

Question

I need to stock some datas in my application. I know that i can do it like this:

class:

public class MyApplication extends Application {

    private String someVariable;

    public String getSomeVariable() {
        return someVariable;
    }

    public void setSomeVariable(String someVariable) {
        this.someVariable = someVariable;
    }
}

Implementation:

MyApp appState = ((MyApp)getApplicationContext());
String state = appState.getSomeVariable();

This is working if i'm in an activity.

But if i'm in a class not extended from Activity, how can I access at my datas?

thanks in advance for your help!

Answer 1

You can use a Singleton design pattern. You can then use it anywhere, because it has static access.

public class SingletonClass {
private static SingletonClass _instance = null;
private int _value = 0;

private SingletonClass() {
}

public static SingletonClass getInstance() {
    if (_instance == null)
        _instance = new SingletonClass();
    return _instance;
}

public int getValue() {
    return _value;
}

public void setValue(int value) {
    _value = value;
}

}

and then access it like this:

SingletonClass.getInstance().getValue();

Note: This is a good and easy workaround for some programming problems, but use it very wisely.. it comes with it's problems

Answer 2

Use SharedPrefrences

http://developer.android.com/guide/topics/data/data-storage.html

Answer 3

Perhaps by injecting all the required for a class data via constructor or special setter, I would suggest former one. ( Constructor Injection vs. Setter Injection )

There are more solutions like static fields but personally I do not like this approach since statics sometimes makes unit testing a bit messy.

BTW, what kind of variables you want to share?

Answer 4

I use, it may be gruesome to some, a class with static variables, that you can retrieve from every class in the app.

Just create a class with all the field as static, and you can use them throughout your app. It doesn't get erased, only when stopping the app.

You could also just add static variables to your application class.

Answer 5

You can use static methods (or variables if they are public). It's really a little messy, but if you group them (methods) in the right way you'll earn happinnes and satisfaction )

static public int getSomeInt(){
     //something
}

And then anywhere in your app use

int x=MyApplication.getSomeInt();

By the way, using this style, you don't need to extend Application class. It's better to create an abstract class for such purposes.

Answer 6

Pass the context of your activity as a param to the method or class:

// ...
public void doStuff(Context context) {
    // for example, to retrieve and EditText
    EditText et = context.findViewById(R.id.editText1);
}

then, on your activity, you would do:

// ...
MyClass myClass = new MyClass();
// ...
myClass.doStuff(this);
// ...