Glide源码解读之绑定生命周期

今天有空，稍微解读了一下glide加载图片框架源码，glide源码比较多，除了弄清楚主流程，对我编程有帮助的，我都会记录下来。

我这里不会一步一步详细解读源码，因为其他博客一大堆，我这里主要讲解一下原理；

绑定生命周期，不用我们自己在onStart，onStop去调用，这种思想很好，所以，值得借鉴。

主要实现原理是创建一个无UI的Fragment添加（绑定）到当前的Activity（或其他Fragment），通过重写Fragment的onStart和onStop方法，通知RequestManager任务改变状态。

源码如下：

外观类：RequestManagerRetriever

package com.johan.glide;

import android.os.Handler;
import android.os.Looper;
import android.os.Message;

import androidx.annotation.NonNull;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentActivity;
import androidx.fragment.app.FragmentManager;

import java.util.HashMap;
import java.util.Map;

public class RequestManagerRetriever implements Handler.Callback {

    private static RequestManagerRetriever instance;

    public static RequestManagerRetriever getInstance() {
        if (instance == null) {
            synchronized (RequestManagerRetriever.class) {
                if (instance == null) {
                    instance = new RequestManagerRetriever();
                }
            }
        }
        return instance;
    }

    private Map<FragmentManager, RequestManagerFragment> tempMap;
    private Handler handler;

    public RequestManagerRetriever() {
        tempMap = new HashMap<>();
        handler = new Handler(Looper.getMainLooper(), this);
    }

    public RequestManager getRequestManager(FragmentActivity fragmentActivity) {
        return getRequestManager(fragmentActivity.getSupportFragmentManager());
    }

    public RequestManager getRequestManager(Fragment fragment) {
        return getRequestManager(fragment.getChildFragmentManager());
    }

    private RequestManager getRequestManager(FragmentManager fragmentManager) {
        // 从 FragmentManager 通过 tag 获取 Fragment
        RequestManagerFragment managerFragment = (RequestManagerFragment) fragmentManager.findFragmentByTag("com.johan.glide");
        if (managerFragment == null) {
            // 从临时缓存获取 Fragment
            // 为什么要用到临时缓存呢？
            // 比如连续两次调用 getRequestManager 方法
            // 因为 fragmentManager.beginTransaction().add(managerFragment, "com.johan.glide").commitAllowingStateLoss(); 这句代码执行之后呢
            // 创建的 Fragment 不会马上能被 fragmentManager.findFragmentByTag("com.johan.glide") 找到
            // 防止重复添加到 FragmentManager
            managerFragment = tempMap.get(fragmentManager);
            if (managerFragment == null) {
                // 创建
                managerFragment = new RequestManagerFragment();
                // 加入临时缓存
                tempMap.put(fragmentManager, managerFragment);
                // 添加到 FragmentManager
                fragmentManager.beginTransaction().add(managerFragment, "com.johan.glide").commitAllowingStateLoss();
                // 通知移除临时缓存
                handler.obtainMessage(0, fragmentManager).sendToTarget();
            }
        }
        // 先从 RequestManagerFragment 获取 RequestManager
        RequestManager manager = managerFragment.getRequestManager();
        if (manager == null) {
            // 创建
            manager = new RequestManager(managerFragment.getActivityLifeCycle());
            // 设置
            managerFragment.setRequestManager(manager);
        }
        return manager;
    }

    @Override
    public boolean handleMessage(@NonNull Message message) {
        //  移除临时缓存
        tempMap.remove((FragmentManager) message.obj);
        return true;
    }

}

无 UI Fragment：RequestManagerFragment

package com.johan.glide;

import android.util.Log;

import androidx.fragment.app.Fragment;

public class RequestManagerFragment extends Fragment {

    private ActivityLifeCycle activityLifeCycle;
    private RequestManager requestManager;

    public RequestManagerFragment() {
        activityLifeCycle = new ActivityLifeCycle();
    }

    public ActivityLifeCycle getActivityLifeCycle() {
        return activityLifeCycle;
    }

    public void setRequestManager(RequestManager requestManager) {
        this.requestManager = requestManager;
    }

    public RequestManager getRequestManager() {
        return requestManager;
    }

    @Override
    public void onStart() {
        super.onStart();
        Log.e("glide", "RequestManagerFragment onStart --------- ");
        // 生命周期回调
        if (activityLifeCycle != null) {
            activityLifeCycle.onStart();
        }
    }

    @Override
    public void onStop() {
        super.onStop();
        Log.e("glide", "RequestManagerFragment onStop --------- ");
        // 生命周期回调
        if (activityLifeCycle != null) {
            activityLifeCycle.onStop();
        }
    }

}

生命周期监听接口：LifeCycleListener

public interface LifeCycleListener {

    void onStart();

    void onStop();

}

生命周期接听接口管理者：ActivityLifeCycle

package com.johan.glide;

import java.util.ArrayList;
import java.util.List;

public class ActivityLifeCycle implements LifeCycleListener {

    private List<LifeCycleListener> lifeCycleListeners;

    public ActivityLifeCycle() {
        lifeCycleListeners = new ArrayList<>();
    }

    public void addLifeCycleListener(LifeCycleListener lifeCycleListener) {
        lifeCycleListeners.add(lifeCycleListener);
    }

    public void removeLifeCycleListener(LifeCycleListener lifeCycleListener) {
        lifeCycleListeners.remove(lifeCycleListener);
    }

    @Override
    public void onStart() {
        for (LifeCycleListener lifeCycleListener : lifeCycleListeners) {
            lifeCycleListener.onStart();
        }
    }

    @Override
    public void onStop() {
        for (LifeCycleListener lifeCycleListener : lifeCycleListeners) {
            lifeCycleListener.onStop();
        }
    }

}

任务管理者：RequestManager

package com.johan.glide;

import android.util.Log;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

public class RequestManager implements LifeCycleListener {

    private ExecutorService executorService;
    private Future future;

    public RequestManager(ActivityLifeCycle activityLifeCycle) {
        executorService = Executors.newCachedThreadPool();
        // 监听生命周期
        activityLifeCycle.addLifeCycleListener(this);
    }

    /**
     * 模拟耗时操作
     */
    public void execute() {
        future = executorService.submit(new Runnable() {
            @Override
            public void run() {
                try {
                    for (int i = 0; i < 100; i++) {
                        Log.e("glide", this + " execute " + i);
                        Thread.sleep(1000);
                    }
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });
    }

    @Override
    public void onStart() {
        Log.e("glide", "request start --------------");
    }

    @Override
    public void onStop() {
        Log.e("glide", "request stop --------------");
        // 停止耗时操作
        future.cancel(true);
        executorService.shutdown();
    }

}

我想可以用这种思想带到我们平常在Activity执行耗时操作中，这样我们的耗时操作就可以和我们的Activity生命周期一样，避免内存泄漏！！！

这里先做一个记录，继续分析glide源码！！！！！

本文地址：https://blog.csdn.net/JohanMan/article/details/110533218