[移动开发]addIdleHandler代码不执行

关于android启动速度的优化，相信大家都会用到IdleHandler去处理一些空闲任务，如下

 Looper.myQueue().addIdleHandler(new MessageQueue.IdleHandler() {
            @Override
            public boolean queueIdle() {
            	//处理空闲任务
              return false;
            }
        });

既然是想提高启动速度，那么IdleHandler基本上都用在MainActivity的onCreate中，此时进入到app主页了，等待空闲时去提前执行一些非必要的初始化信息，或者进行预加载。

项目中之前版本的功能都是正常的，这段代码也能执行到，突然新版本这里面代码始终走不到，那么意味着里面初始化信息都将失效，启动速度优化也功亏一篑，好不容易做的功能，又被打回原形。

其实这个空闲handler代码不执行，根本原因只有一个，就是它不空闲并且很忙，没空处理你的空闲任务，那么为什么他会很忙呢？肯定是有地方在不停更新页面。虽然问题基本上可以定位在新老版本开发的需求中间，但是那么多代码，怎么去定位这个问题呢？

别急！别急！往下看！

我们知道整个app都是在loop中的死循环中的

for (;;) {
    Message msg = queue.next(); 
    if (msg == null) {
        return;
    }
    final Printer logging = me.mLogging;
    if (logging != null) {
        logging.println(">>>>> Dispatching to " + msg.target + " " +
                msg.callback + ": " + msg.what);
    }
    //省略代码。。。
    if (logging != null) {
        logging.println("<<<<< Finished to " + msg.target + " " + msg.callback);
    }
  }

方法中已经提供了log的打印，而且是成对出现的，开始和结束都会打印，由此我们可以尝试打印handler处理的日志，到底是谁在一直更新。

我们在addIdleHandler之前添加log：

Looper.myLooper().setMessageLogging(new LogPrinter(Log.ERROR, "Ajiang"));

这样上面的死循环代码的logging就不为空，打印如下所示：

E/Ajiang: >>>>> Dispatching to Handler (android.view.ViewRootImpl$ViewRootHandler) {301f6b1} android.view.ViewRootImpl$SendWindowContentChangedAccessibilityEvent@d7faa81: 0
        E/Ajiang: <<<<< Finished to Handler (android.view.ViewRootImpl$ViewRootHandler) {301f6b1} android.view.ViewRootImpl$SendWindowContentChangedAccessibilityEvent@d7faa81
E/Ajiang: >>>>> Dispatching to Handler (android.view.Choreographer$FrameHandler) {90e4ced} android.view.Choreographer$FrameDisplayEventReceiver@2d52722: 0
        E/Ajiang: <<<<< Finished to Handler (android.view.Choreographer$FrameHandler) {90e4ced} android.view.Choreographer$FrameDisplayEventReceiver@2d52722
        E/Ajiang: >>>>> Dispatching to Handler (android.view.ViewRootImpl$ViewRootHandler) {301f6b1} com.xxx.xxx.recyclerview.AutoPollRecyclerView$AutoPollTask@613a6b2: 0
        E/Ajiang: <<<<< Finished to Handler (android.view.ViewRootImpl$ViewRootHandler) {301f6b1} com.xxx.xxx.recyclerview.AutoPollRecyclerView$AutoPollTask@613a6b2
        E/Ajiang: >>>>> Dispatching to Handler (android.view.ViewRootImpl$ViewRootHandler) {301f6b1} android.view.View$SendViewScrolledAccessibilityEvent@363299b: 0
        E/Ajiang: <<<<< Finished to Handler (android.view.ViewRootImpl$ViewRootHandler) {301f6b1} android.view.View$SendViewScrolledAccessibilityEvent@363299b
        E/Ajiang: >>>>> Dispatching to Handler (android.view.Choreographer$FrameHandler) {90e4ced} android.view.Choreographer$FrameDisplayEventReceiver@2d52722: 0
        E/Ajiang: <<<<< Finished to Handler (android.view.Choreographer$FrameHandler) {90e4ced} android.view.Choreographer$FrameDisplayEventReceiver@2d52722
        E/Ajiang: >>>>> Dispatching to Handler (android.view.ViewRootImpl$ViewRootHandler) {301f6b1} com.xxx.xxx.recyclerview.AutoPollRecyclerView$AutoPollTask@613a6b2: 0
        E/Ajiang: <<<<< Finished to Handler (android.view.ViewRootImpl$ViewRootHandler) {301f6b1} com.xxx.xxx.recyclerview.AutoPollRecyclerView$AutoPollTask@613a6b2
        E/Ajiang: >>>>> Dispatching to Handler (android.view.Choreographer$FrameHandler) {90e4ced} null: 2
        E/Ajiang: <<<<< Finished to Handler (android.view.Choreographer$FrameHandler) {90e4ced} null
        E/Ajiang: >>>>> Dispatching to Handler (android.view.Choreographer$FrameHandler) {90e4ced} android.view.Choreographer$FrameDisplayEventReceiver@2d52722: 0
        E/Ajiang: <<<<< Finished to Handler (android.view.Choreographer$FrameHandler) {90e4ced} android.view.Choreographer$FrameDisplayEventReceiver@2d52722
        E/Ajiang: >>>>> Dispatching to Handler (android.view.ViewRootImpl$ViewRootHandler) {301f6b1} com.xxx.xxx.recyclerview.AutoPollRecyclerView$AutoPollTask@613a6b2: 0
        E/Ajiang: <<<<< Finished to Handler (android.view.ViewRootImpl$ViewRootHandler) {301f6b1} com.xxx.xxx.recyclerview.AutoPollRecyclerView$AutoPollTask@613a6b2
        E/Ajiang: >>>>> Dispatching to Handler (android.view.Choreographer$FrameHandler) {90e4ced} android.view.Choreographer$FrameDisplayEventReceiver@2d52722: 0
        E/Ajiang: <<<<< Finished to Handler (android.view.Choreographer$FrameHandler) {90e4ced} android.view.Choreographer$FrameDisplayEventReceiver@2d52722
        E/Ajiang: >>>>> Dispatching to Handler (android.view.ViewRootImpl$ViewRootHandler) {301f6b1} com.xxx.xxx.recyclerview.AutoPollRecyclerView$AutoPollTask@613a6b2: 0
        E/Ajiang: <<<<< Finished to Handler (android.view.ViewRootImpl$ViewRootHandler) {301f6b1} com.xxx.xxx.recyclerview.AutoPollRecyclerView$AutoPollTask@613a6b2

可以很明显的发现日志一直在循环打印，而且速度很快，很容易定位到AutoPollRecyclerView这个类有问题，于是查看发现这是个自动滚动的Recyclerview，还没到这个页面对应的tab就已经开始滚动了，所以这肯定是有问题的，改成切换到对应页面再去滚动。

本以为大功告成，于是重新跑遍代码，发现日志仍然再循环滚动。

E/Ajiang: >>>>> Dispatching to Handler (android.view.ViewRootImpl$ViewRootHandler) {f0cee21} com.xxx.xxx.ui.adapter.recommend.HomeChallengeAdapter$7$1@8020ce7: 0
        E/Ajiang: <<<<< Finished to Handler (android.view.ViewRootImpl$ViewRootHandler) {f0cee21} com.xxx.xxx.ui.adapter.recommend.HomeChallengeAdapter$7$1@8020ce7
        E/Ajiang: >>>>> Dispatching to Handler (android.view.Choreographer$FrameHandler) {a4b9c07} android.view.Choreographer$FrameDisplayEventReceiver@25c134: 0
        E/Ajiang: <<<<< Finished to Handler (android.view.Choreographer$FrameHandler) {a4b9c07} android.view.Choreographer$FrameDisplayEventReceiver@25c134
        E/Ajiang: >>>>> Dispatching to Handler (android.os.Handler) {e88c10f} null: 2
        E/Ajiang: <<<<< Finished to Handler (android.os.Handler) {e88c10f} null
        E/Ajiang: >>>>> Dispatching to Handler (android.os.Handler) {51748c6} null: 1
        E/Ajiang: <<<<< Finished to Handler (android.os.Handler) {51748c6} null
        E/Ajiang: >>>>> Dispatching to Handler (android.view.ViewRootImpl$ViewRootHandler) {f0cee21} com.xxx.xxx.ui.adapter.recommend.HomeChallengeAdapter$7$1@a781094: 0
        E/Ajiang: <<<<< Finished to Handler (android.view.ViewRootImpl$ViewRootHandler) {f0cee21} com.xxx.xxx.ui.adapter.recommend.HomeChallengeAdapter$7$1@a781094
E/Ajiang: >>>>> Dispatching to Handler (android.view.Choreographer$FrameHandler) {a4b9c07} android.view.Choreographer$FrameDisplayEventReceiver@25c134: 0
        E/Ajiang: <<<<< Finished to Handler (android.view.Choreographer$FrameHandler) {a4b9c07} android.view.Choreographer$FrameDisplayEventReceiver@25c134
        E/Ajiang: >>>>> Dispatching to Handler (android.view.ViewRootImpl$ViewRootHandler) {f0cee21} com.xxx.xxx.ui.adapter.recommend.HomeChallengeAdapter$7$1@a4573d: 0
        E/Ajiang: <<<<< Finished to Handler (android.view.ViewRootImpl$ViewRootHandler) {f0cee21} com.xxx.xxx.ui.adapter.recommend.HomeChallengeAdapter$7$1@a4573d

好家伙，竟然还有一处，定位代码

ll_challenge_content.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
    @Override
    public void onGlobalLayout() {
        ll_challenge_content.post(new Runnable() {
            public void run() {
                ll_challenge_content.requestLayout();
                bgParams.height = ll_challenge_content.getMeasuredHeight() + ScreenUtils.dp2px(55);
            }
        });

    }
});

这一直监听，一直刷，这不得忙到死么。看了下代码逻辑，其实这个地方完全没必要做监听的，后续发现这段代码的确是可以删掉的，就算不能删的话，可以换种思路做，要么加标记位，避免死循环，适当移除监听。

最后跑一遍代码，终于没有死循环的日志了，也能成功进入IdleHandler的执行代码中，启动优化也可以恢复正常了，叹了口气！