获取Application的Context

Posted 2022-12-11 ihrthk

引言

获取Application的Context，这一直是一个比较常见的问题，现在做很多事情都需是context。一般来讲有两种办法。一是封装方法传参，二是封装静态的Application实例。
在我看来这两种办法，都不是很好。第一种的问题是在方法嵌套调用的时候有繁琐，常常出现的问题是，第一个方法需要context参数，直到第n级方法的时候才用到这个context。第二个问题是Application的实例只有一个，不需要使用static，官方也反对我们这么多。其次这么写对代码有一定的浸入性。

查看Activity的源码，自己的办法

---

/**
 * Created by zhangls on 2016/7/6.
 */
public class ContextProvider 
    private static Context sContext = null;

    /**
     * Get application context.
     *
     * @return
     */
    public static Context getApplicationContext() 
        if (sContext != null) 
            return sContext;
        
        try 
            //1.先获取到当前的ActivityThread对象
            Class<?> activityThreadClass = Class.forName("android.app.ActivityThread");
            //2.获取ActivityTread的静态方法currentApplication
            Method currentActivityThreadMethod = activityThreadClass.getDeclaredMethod("currentApplication");
            //隐藏Api，设置可访问
            currentActivityThreadMethod.setAccessible(true);
            //3.调用ActivityTread.currentApplication()
            Application currentApplication = (Application) currentActivityThreadMethod.invoke(null);
            sContext = currentApplication.getApplicationContext();
         catch (ClassNotFoundException e) 
            e.printStackTrace();
         catch (NoSuchMethodException e) 
            e.printStackTrace();
         catch (IllegalAccessException e) 
            e.printStackTrace();
         catch (InvocationTargetException e) 
            e.printStackTrace();
        

        if (sContext == null) 
            throw new NullPointerException("Global application uninitialized");
        
        return sContext;
    

    private ContextProvider() 

    

发现一个更好的实现，来自冯森林（https://github.com/oasisfeng/）。

public class App 
    public static final Application INSTANCE;

    static 
        Application app = null;
        try 
            app = (Application) Class.forName("android.app.AppGlobals").getMethod("getInitialApplication").invoke(null);
            if (app == null)
                throw new IllegalStateException("Static initialization of Applications must be on main thread.");
         catch (final Exception e) 
            Log.e("Failed to get current application from AppGlobals." + e.getMessage());
            try 
                app = (Application) Class.forName("android.app.ActivityThread").getMethod("currentApplication").invoke(null);
             catch (final Exception ex) 
                Log.e("Failed to get current application from ActivityThread." + e.getMessage());
            
         finally 
            INSTANCE = app;