Question

在我的静态方法中（参数只有一个字符串），我想使用Dialog（new AlertDialog.Builder(mContext)），但是对话框需要一个活动上下文来构造。如果我不通过反射或其他方法传递外部上下文参数，如何获取当前顶级活动的对象？

public static Activity getActivity() {
    Class activityThreadClass = null;
    try {
        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;
            }
        }
    } catch (ClassNotFoundException e) {
        e.printStackTrace();
    } catch (NoSuchMethodException e) {
        e.printStackTrace();
    } catch (IllegalAccessException e) {
        e.printStackTrace();
    } catch (InvocationTargetException e) {
        e.printStackTrace();
    } catch (NoSuchFieldException e) {
        e.printStackTrace();
    }
    return null;
}

我使用了这段代码，但是当我在非Activity类中调用此方法时，activities为空。

还有其他方法吗？无法使用对话框，只要能够弹出信息就可以被用户看到。点数限制：不从参数中获取上下文。

Answer 1

使用Application.ActivityLifecycleCallbacks

实施例：

class ActivityLifeCycleCallbackImpl implements  Application.ActivityLifecycleCallbacks {

    private Set<Activity> set = new HashSet<>();


    @Override
    public void onActivityStarted(Activity activity) {
        set.add(activity);
    }

    @Override
    public void onActivityStopped(Activity activity) {
        set.remove(activity);

    }

    Activity getCurrentActivity() {
        if (set.isEmpty()) {
            return null;
        }
        return set.iterator().next();
    }


}

并在您的自定义应用程序类中：

    ActivityLifeCycleCallbackImpl activityLifeCycleCallback = new ActivityLifeCycleCallbackImpl();
    @Override
    public void onCreate() { 
        registerActivityLifecycleCallbacks(activityLifeCycleCallback);

}

如何获取当前的顶级活动上下文

1 个答案: