android获取当前界面activity对象

在编写android应用的时候一般跟界面相关的都离不开activity，很多时候我们需要在纯java环境中使用activity对象，一般情况下我们都是靠参数传递去使用。现在我们可以使用纯java代码来获取当前系统中的activity对象，有了activity对象我们就可以做很多想做的事情，比如监听改activity的生命周期，给改activity界面添加浮动view等等。废话少说看下面方法：

	public static Activity getGlobleActivity() throws ClassNotFoundException, IllegalArgumentException, SecurityException, IllegalAccessException, InvocationTargetException, NoSuchMethodException, NoSuchFieldException{
        Class activityThreadClass = Class.forName("android.app.ActivityThread");
        Object activityThread = activityThreadClass.getMethod("currentActivityThread").invoke(null);
        Field activitiesField = activityThreadClass.getDeclaredField("mActivities");
        activitiesField.setAccessible(true);
        Map activities = (Map) activitiesField.get(activityThread);
        for(Object activityRecord:activities.values()){
            Class activityRecordClass = activityRecord.getClass();
            Field pausedField = activityRecordClass.getDeclaredField("paused");
            pausedField.setAccessible(true);
            if(!pausedField.getBoolean(activityRecord)) {
                Field activityField = activityRecordClass.getDeclaredField("activity");
                activityField.setAccessible(true);
                Activity activity = (Activity) activityField.get(activityRecord);
                return activity;
            }
        }
        return null;
      }

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