工厂模式--以Glide.with为例

1、工厂模式的作用，创建对象，为啥不直接用new 而用工厂模式

原因，1、初始化复杂，耗时，将对象交给工厂来生产，实现高度内聚；2、省略了繁杂的判断条件

 

抽象模式解释非常到位：

https://blog.youkuaiyun.com/qq_33905217/article/details/109029517?ops_request_misc=%257B%2522request%255Fid%2522%253A%2522162114305016780271563578%2522%252C%2522scm%2522%253A%252220140713.130102334..%2522%257D&request_id=162114305016780271563578&biz_id=0&utm_medium=distribute.pc_search_result.none-task-blog-2~all~top_positive~default-1-109029517.first_rank_v2_pc_rank_v29&utm_term=%E5%B7%A5%E5%8E%82%E6%A8%A1%E5%BC%8F&spm=1018.2226.3001.4187

 

Glide.with(Context context)

前面说到，Glide 生命周期的时候，说过Context 与fragment 绑定，requestManager 与 fragment 绑定实现了生命周期管理。

现在看下如何实现根据不同的context 去拿到requestManger，对用户来说仅需要知道把context 放入即可，工厂类内部根据传入的context 创建与之对应的生命周期。

Glide.class:以传入activity 为例

public static RequestManager with(Context context) {
//单例模式创建工程实例
    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(FragmentActivity activity) {
    RequestManagerRetriever retriever = RequestManagerRetriever.get();
    return retriever.get(activity);
}

@TargetApi(11)
public static RequestManager with(Fragment fragment) {
    RequestManagerRetriever retriever = RequestManagerRetriever.get();
    return retriever.get(fragment);
}

public static RequestManager with(android.support.v4.app.Fragment fragment) {
    RequestManagerRetriever retriever = RequestManagerRetriever.get();
    return retriever.get(fragment);
}

看下工厂类：RequestManagerRetriever

public class RequestManagerRetriever implements Callback {
private static final RequestManagerRetriever INSTANCE = new RequestManagerRetriever();
public static RequestManagerRetriever get() {
    return INSTANCE;
}

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 this.get((FragmentActivity)context);
            }

            if (context instanceof Activity) {
                return this.get((Activity)context);
            }

            if (context instanceof ContextWrapper) {
                return this.get(((ContextWrapper)context).getBaseContext());
            }
        }

        return this.getApplicationManager(context);
    }
}
......

@TargetApi(11)
public RequestManager get(Activity activity) {
    if (!Util.isOnBackgroundThread() && VERSION.SDK_INT >= 11) {
        assertNotDestroyed(activity);
        FragmentManager fm = activity.getFragmentManager();
        return this.fragmentGet(activity, fm);
    } else {
        return this.get(activity.getApplicationContext());
    }
}
......

@TargetApi(11)
RequestManager fragmentGet(Context context, FragmentManager fm) {
    RequestManagerFragment current = this.getRequestManagerFragment(fm);
    RequestManager requestManager = current.getRequestManager();
    if (requestManager == null) {
        requestManager = new RequestManager(context, current.getLifecycle(), current.getRequestManagerTreeNode());
        current.setRequestManager(requestManager);
    }

    return requestManager;
}

根据context 创建的fragment 的TAG 判断requestManger 是否存在

@TargetApi(17)
RequestManagerFragment getRequestManagerFragment(FragmentManager fm) {
    RequestManagerFragment current = (RequestManagerFragment)fm.findFragmentByTag("com.bumptech.glide.manager");
    if (current == null) {
        current = (RequestManagerFragment)this.pendingRequestManagerFragments.get(fm);
        if (current == null) {
            current = new RequestManagerFragment();
            this.pendingRequestManagerFragments.put(fm, current);
            fm.beginTransaction().add(current, "com.bumptech.glide.manager").commitAllowingStateLoss();
            this.handler.obtainMessage(1, fm).sendToTarget();
        }
    }

    return current;
}

 

}