Glide源码分析with的差别

Glide提供with重载的方法

    public static RequestManager with(Context context) {
        RequestManagerRetriever retriever = RequestManagerRetriever.get();
        return retriever.get(context);
    }

    public static RequestManager with(Activity activity) {
        RequestManagerRetriever retriever = RequestManagerRetriever.get();
        return retriever.get(activity);
    }

    public static RequestManager with(Fragment fragment) {
        RequestManagerRetriever retriever = RequestManagerRetriever.get();
        return retriever.get(fragment);
    }

在上面的3个方法都会调用retriever.get(XXX)，所以get也是一个重载方法

    public RequestManager get(Context context) {
        if (context == null) {
            throw new IllegalArgumentException("You cannot start a load on a null Context");
        } else if (Util.isOnMainThread() && !(context instanceof Application)) {
            if (context instanceof FragmentActivity) {
                return get((FragmentActivity) context);
            } else if (context instanceof Activity) {
                return get((Activity) context);
            } else if (context instanceof ContextWrapper) {
                return get(((ContextWrapper) context).getBaseContext());
            }
        }

        return getApplicationManager(context);
    }

    public RequestManager get(FragmentActivity activity) {
        if (Util.isOnBackgroundThread()) {
            return get(activity.getApplicationContext());
        } else {
            assertNotDestroyed(activity);
            FragmentManager fm = activity.getSupportFragmentManager();
            return supportFragmentGet(activity, fm);
        }
    }

    public RequestManager get(Fragment fragment) {
        if (fragment.getActivity() == null) {
            throw new IllegalArgumentException("You cannot start a load on a fragment before it is attached");
        }
        if (Util.isOnBackgroundThread()) {
            return get(fragment.getActivity().getApplicationContext());
        } else {
            FragmentManager fm = fragment.getChildFragmentManager();
            return supportFragmentGet(fragment.getActivity(), fm);
        }
    }

从代码看出
传FragmentActivity和Fragment都会通过FragmentManager（getSupportFragmentManager/getChildFragmentManager）来添加一个fragment 来管理，一个Activity只有一个Fragment的话，传的对象是Activity/Fragment 感觉没区别，一个Activity有多个Fragment的话，传的对象是Activity/Fragment 感觉好像区别

    RequestManager supportFragmentGet(Context context, FragmentManager fm) {
        SupportRequestManagerFragment current = getSupportRequestManagerFragment(fm);
        RequestManager requestManager = current.getRequestManager();
        if (requestManager == null) {
            requestManager = new RequestManager(context, current.getLifecycle(), current.getRequestManagerTreeNode());
            current.setRequestManager(requestManager);
        }
        return requestManager;
    }

在getSupportRequestManagerFragment方法里面会通过Tag寻找是否存在fragment

    SupportRequestManagerFragment getSupportRequestManagerFragment(final FragmentManager fm) {
        SupportRequestManagerFragment current = (SupportRequestManagerFragment) fm.findFragmentByTag(


            FRAGMENT_TAG);
        if (current == null) {
            current = pendingSupportRequestManagerFragments.get(fm);
            if (current == null) {
                current = new SupportRequestManagerFragment();
                pendingSupportRequestManagerFragments.put(fm, current);
                fm.beginTransaction().add(current, FRAGMENT_TAG).commitAllowingStateLoss();
                handler.obtainMessage(ID_REMOVE_SUPPORT_FRAGMENT_MANAGER, fm).sendToTarget();
            }
        }
        return current;
    }

最后我们需要注意，不管传什么对象，Glide可能会抛出异常导致程序挂掉，所以封装GlideUtils的时候try下

throw new IllegalArgumentException("You cannot start a load on a null Context");
throw new IllegalArgumentException("You cannot start a load on a fragment before it is attached");

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