Android 获取当前Activity的方式

爱被打了一巴掌 2022-09-07 09:58 802阅读 0赞

#### 一、背景 ####

在开发的过程中有时候需要获取最上层的activity。

#### 二、获取方式 ####

*  通过RunningTaskInfo的topActivity获取当前Activity实例。通过该种方式获取的Activity，只能保证其已经执行了Activity.onCreate方法，不能保证是否执行了Activity.onResume方法。该方法在api 21以后已经被禁，使用需谨慎。

public static String getCurrentActivityName(Context context) { 
        ActivityManager am = (ActivityManager) context.getSystemService(Activity.ACTIVITY_SERVICE);
    
        List<ActivityManager.RunningTaskInfo> taskInfo = am.getRunningTasks(1);
    
        ComponentName componentInfo = taskInfo.get(0).topActivity;
        return componentInfo.getClassName();
    }

*  通过Android 4.0之后提供的ActivityLifecycleCallbacks接口监听当前的Activity实例，可以在onActivityCreated或者onActivityResumed当中获取到。建议在onActivityResumed当中去获取，同时最好以软引用或者弱引用的方式持有，防止OOM。（其中XxxApplication是你的工程Application）

if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.ICE_CREAM_SANDWICH) { 
       registerActivityLifecycleCallbacks(new ActivityLifeCycleCallbackAdapter() { 
            @Override
            public void onActivityResumed(Activity activity) { 
                super.onActivityResumed(activity);
                activityRef = new SoftReference<Activity>(activity);
            }
        });
    }

public static boolean isActivityResumed(Class<?> clazz) { 
       if (clazz == null) { 
            throw new NullPointerException("activity class can not be null");
        }
    
        SoftReference<Activity> currentActivityRef = XxxApplication
                .getCurrentActivityRef();
    
        if (currentActivityRef == null) { 
            return false;
        }
    
        Activity currentActivity = currentActivityRef.get();
        if (currentActivity == null || !clazz.isInstance(currentActivity)) { 
            return false;
        }
    
        return true;
    }

*  手写Activity管理栈，可以使用Stack或者List等存储已经执行了Activity.onCreate或者Activity.onResume方法的Activity，并相应在Activity.onPause或者Activity.onDestroy中移除。
 *  反射方式

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