如何在FloatingActionButton/Button Click事件中使用Coroutine

提问者：小点点

如何在FloatingActionButton/Button Click事件中使用Coroutine

我有一个FloatingActionButton，点击它会从网上下载一些URL。我想从setOnClickListener内部启动这个函数，然后让它在后台做所有的处理。

我已经使用AsyncTask做了我想做的事情，但是后来有人建议使用协同任务。

activity内部:

findViewById<FloatingActionButton>(R.id.fab).setOnClickListener { view ->
           
            val currentChapUrl = "https://www.novel.com/chap1.html"  
            GlobalScope.launch { downloadChapters(applicationContext,currentChapUrl) } 
        }

downloadChapters函数如下所示:

suspend fun downloadChapters(context : Context, startingChapUrl : String) : String {
   //download chapters.
   //show some toast messages

}

该应用程序在点击按钮时崩溃。

日志CAT:

2020-08-01 17:03:38.559 6937-6985/com.example.daoreader E/eglCodecCommon: glUtilsParamSize: unknow param 0x000085b5
2020-08-01 17:03:38.559 6937-6985/com.example.daoreader E/eglCodecCommon: glUtilsParamSize: unknow param 0x000085b5
2020-08-01 17:03:39.095 6937-6937/com.example.daoreader I/Choreographer: Skipped 32 frames!  The application may be doing too much work on its main thread.
2020-08-01 17:03:39.124 6937-6985/com.example.daoreader E/eglCodecCommon: glUtilsParamSize: unknow param 0x000085b5
2020-08-01 17:03:39.125 6937-6985/com.example.daoreader E/eglCodecCommon: glUtilsParamSize: unknow param 0x000085b5
2020-08-01 17:03:39.163 6937-6985/com.example.daoreader E/eglCodecCommon: glUtilsParamSize: unknow param 0x000085b5
2020-08-01 17:03:39.163 6937-6985/com.example.daoreader E/eglCodecCommon: glUtilsParamSize: unknow param 0x000085b5
2020-08-01 17:03:39.208 6937-6985/com.example.daoreader E/eglCodecCommon: glUtilsParamSize: unknow param 0x000085b5
2020-08-01 17:03:39.209 6937-6985/com.example.daoreader E/eglCodecCommon: glUtilsParamSize: unknow param 0x000085b5
    
    
    --------- beginning of crash
2020-08-01 17:03:39.211 6937-7086/com.example.daoreader E/AndroidRuntime: FATAL EXCEPTION: DefaultDispatcher-worker-1
    Process: com.example.daoreader, PID: 6937
    java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
        at android.os.Handler.<init>(Handler.java:200)
        at android.os.Handler.<init>(Handler.java:114)
        at android.widget.Toast$TN$2.<init>(Toast.java:336)
        at android.widget.Toast$TN.<init>(Toast.java:336)
        at android.widget.Toast.<init>(Toast.java:103)
        at android.widget.Toast.makeText(Toast.java:256)
        at com.example.daoreader.WebviewActivity.downloadChapters(WebviewActivity.kt:65)
        at com.example.daoreader.WebviewActivity$onCreate$1$1.invokeSuspend(WebviewActivity.kt:32)
        at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
        at kotlinx.coroutines.DispatchedTask.run(Dispatched.kt:241)
        at kotlinx.coroutines.scheduling.CoroutineScheduler.runSafely(CoroutineScheduler.kt:594)
        at kotlinx.coroutines.scheduling.CoroutineScheduler.access$runSafely(CoroutineScheduler.kt:60)
        at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.run(CoroutineScheduler.kt:740)
    
    
    --------- beginning of system
2020-08-01 17:03:39.257 6937-6985/com.example.daoreader E/eglCodecCommon: glUtilsParamSize: unknow param 0x000085b5
2020-08-01 17:03:39.257 6937-6985/com.example.daoreader E/eglCodecCommon: glUtilsParamSize: unknow param 0x000085b5
2020-08-01 17:03:39.307 6937-6985/com.example.daoreader E/eglCodecCommon: glUtilsParamSize: unknow param 0x000085b5
2020-08-01 17:03:39.307 6937-6985/com.example.daoreader E/eglCodecCommon: glUtilsParamSize: unknow param 0x000085b5
2020-08-01 17:03:39.394 6937-6985/com.example.daoreader E/eglCodecCommon: glUtilsParamSize: unknow param 0x000085b5
2020-08-01 17:03:39.394 6937-6985/com.example.daoreader E/eglCodecCommon: glUtilsParamSize: unknow param 0x000085b5
2020-08-01 17:03:39.487 6937-6985/com.example.daoreader E/eglCodecCommon: glUtilsParamSize: unknow param 0x000085b5
2020-08-01 17:03:39.487 6937-6985/com.example.daoreader E/eglCodecCommon: glUtilsParamSize: unknow param 0x000085b5
2020-08-01 17:03:39.565 6937-6985/com.example.daoreader E/eglCodecCommon: glUtilsParamSize: unknow param 0x000085b5
2020-08-01 17:03:39.566 6937-6985/com.example.daoreader E/eglCodecCommon: glUtilsParamSize: unknow param 0x000085b5
2020-08-01 17:03:39.581 6937-6985/com.example.daoreader D/EGL_emulation: eglMakeCurrent: 0xaa205000: ver 2 0 (tinfo 0xaa2034c0)
2020-08-01 17:03:39.595 6937-6985/com.example.daoreader D/EGL_emulation: eglMakeCurrent: 0xaa205000: ver 2 0 (tinfo 0xaa2034c0)
2020-08-01 17:03:39.658 6937-6985/com.example.daoreader E/eglCodecCommon: glUtilsParamSize: unknow param 0x000085b5
2020-08-01 17:03:39.658 6937-6985/com.example.daoreader E/eglCodecCommon: glUtilsParamSize: unknow param 0x000085b5
2020-08-01 17:03:39.714 6937-6985/com.example.daoreader D/EGL_emulation: eglMakeCurrent: 0xaa205000: ver 2 0 (tinfo 0xaa2034c0)
2020-08-01 17:03:39.727 6937-6985/com.example.daoreader D/OpenGLRenderer: endAllActiveAnimators on 0x9232d500 (RippleDrawable) with handle 0x92021280
2020-08-01 17:03:40.051 6937-6985/com.example.daoreader E/eglCodecCommon: glUtilsParamSize: unknow param 0x000085b5
2020-08-01 17:03:40.051 6937-6985/com.example.daoreader E/eglCodecCommon: glUtilsParamSize: unknow param 0x000085b5
2020-08-01 17:03:40.094 6937-6985/com.example.daoreader E/eglCodecCommon: glUtilsParamSize: unknow param 0x000085b5
2020-08-01 17:03:40.094 6937-6985/com.example.daoreader E/eglCodecCommon: glUtilsParamSize: unknow param 0x000085b5

共2个答案

匿名用户

它正在崩溃，因为您显示的toast不在主线程中。

GlobalScope.launch默认地在另一个线程Dispatchers.Default中运行代码。

所以您需要做的是，在显示toast之前，您应该将线程更改为主线程，如下所示

suspend fun downloadChapters(context : Context, startingChapUrl : String) : String {
   //download chapters.
   
   withContext(Dispatchers.Main) {
       // Show Toast here
   }
}

匿名用户

避免使用GlobalScope。您应该使用LifeCycleScope在视图中启动一个协同关系。

您需要首先将androidx.lifecycle:lifecycle-runtime-ktx:{version}添加到您的gradle文件中。

假设您想在祝酒词中显示downloadchapses返回的内容，那么我会这样做:

activity内部:

findViewById<FloatingActionButton>(R.id.fab).setOnClickListener { view ->
    lifecycleScope.launch {
        val message = downloadChapters(this@MyActivity, "https://www.novel.com/chap1.html")
        //Show toast here
    }
}

碎片内部:

findViewById<FloatingActionButton>(R.id.fab).setOnClickListener { view ->
    viewLifecycleOwner.lifecycleScope.launch {
        val message = downloadChapters(context, "https://www.novel.com/chap1.html")
        //Show toast here
    }
}

由于LifeCycleScope.launch在主线程上运行，因此必须在DownloadChapses期间将其上下文更改为Dispatchers.io，因此您的方法应该如下所示:

suspend fun downloadChapters(context : Context, startingChapUrl : String) : String = withContext(Dispatchers.IO) {
    //download chapters.
    "This is my message" //Return your message here
}

在DownloadChapters内无法更新视图，除非在此之前移动到Dispatchers.Main，否则将引发异常。我宁愿在调用那个方法之后再做。