Best way to get an Application Context into a static method in Android

问题

I'm working on an Android application that has several Activities. In it I have a class with several static methods. I would like to be able to call these methods from the different Activities. I'm using the static methods to load data from an xml file via a XmlResourceParser. To create a XmlResourceParser requires a call on the Application Context. So my question is, what is the best way to get a reference to the Application Context into the static methods? Have each Activity get it and pass it in? Store it somehow in a global variable?

回答1:

The better way would be to pass the Activity object as parameter to the static functions.

AFAIK, there is no such method which will give you the application context in the static method.

回答2:

I am not sure this is going to work all the time but it works for me now:

public class myActivity extends ListActivity
{
    public static Context baseContext;

    public void onCreate(Bundle savedInstanceState) 
    {
        baseContext = getBaseContext();
    }

Then you may use the static in your package:

myApplication.baseContext

回答3:

This should get you access to applicationContext from anywhere allowing you to get applicationContext anywhere that can use it; Toast, getString(), sharedPreferences, etc. I have used this to get applicationContext inside of static methods multiple times.

The Singleton:

package com.domain.packagename;

import android.content.Context;

/**
 * Created by Versa on 10.09.15.
 */
public class ApplicationContextSingleton {
    private static PrefsContextSingleton mInstance;
    private Context context;

    public static ApplicationContextSingleton getInstance() {
        if (mInstance == null) mInstance = getSync();
        return mInstance;
    }

    private static synchronized ApplicationContextSingleton getSync() {
        if (mInstance == null) mInstance = new PrefsContextSingleton();
        return mInstance;
    }

    public void initialize(Context context) {
        this.context = context;
    }

    public Context getApplicationContext() {
        return context;
    }

}

Initialize the Singleton in your Application subclass:

package com.domain.packagename;

import android.app.Application;

/**
 * Created by Versa on 25.08.15.
 */
public class mApplication extends Application {

    @Override
    public void onCreate() {
        super.onCreate();
        ApplicationContextSingleton.getInstance().initialize(this);
    }
}

If I´m not wrong, this gives you a hook to applicationContext everywhere, call it with ApplicationContextSingleton.getInstance.getApplicationContext(); You shouldn´t need to clear this at any point, as when application closes, this goes with it anyway.

Remember to update AndroidManifest.xml to use this Application subclass:

<?xml version="1.0" encoding="utf-8"?>

<manifest
    xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.domain.packagename"
    >

<application
    android:allowBackup="true"
    android:name=".mApplication" <!-- This is the important line -->
    android:label="@string/app_name"
    android:theme="@style/AppTheme"
    android:icon="@drawable/app_icon"
    >

Please let me know if you see anything wrong here, thank you. :)

回答4:

There's a post in Sane Tricks For InsaneWorld blog with an answer. It says you can replace the Application object with your own subclass and then keep the app context statically there. You can find example code in the post.

The original blog post - http://uquery.blogspot.co.il/2011/08/how-to-get-application-context.html

来源：https://stackoverflow.com/questions/2785670/best-way-to-get-an-application-context-into-a-static-method-in-android

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android

android-context