Kotlin Flow实现线程切换

• • flowOn方法实现线程切换
  • Log结果如下
  • 注意：flowOn方法一般跟在flow耗时流后面，不然可能会造成其他方法也在子线程

 private fun flowOn() {
        lifecycleScope.launch {//主线程
            simpleFlowOn()
                .flowOn(Dispatchers.IO)//子线程执行，耗时操作
                .onStart {//最先开始
                    LogUtils.d("Thread is ${Thread.currentThread().name} onStart")
                }
                .onEach {
                    LogUtils.d("Thread is ${Thread.currentThread().name} onEach")
                }
                .catch { exception ->//异常接收
                    LogUtils.d("Thread is ${Thread.currentThread().name} exception $exception")
                }
                .onCompletion {//整个流完成
                    LogUtils.d("Thread is ${Thread.currentThread().name} onCompletion")
                }
                .collect {//数据接收
                    LogUtils.d("Thread is ${Thread.currentThread().name} collect $it")
                }
        }
    }

 //实现一个流，每秒发送一个数据
    private fun simpleFlowOn(): Flow = flow {
        for (i in 1..3) {
            delay(1000)
            LogUtils.d("Thread is ${Thread.currentThread().name} Emitting $i")
//            if (i == 3) throw IllegalStateException("状态错误")
            emit(i)
        }
    }

	//在主线程开始onStart
    D/FlowFragment: Thread is main onStart
    //发送在子线程
    D/FlowFragment: Thread is DefaultDispatcher-worker-1 Emitting 1
    D/FlowFragment: Thread is main onEach
    //接收在主线程
    D/Collect: Thread is main collect 1
    D/FlowFragment: Thread is DefaultDispatcher-worker-1 Emitting 2
    D/FlowFragment: Thread is main onEach
    D/Collect: Thread is main collect 2
    D/FlowFragment: Thread is DefaultDispatcher-worker-1 Emitting 3
    D/FlowFragment: Thread is main onEach
    D/Collect: Thread is main collect 3
    //最后完成在主线程
    D/FlowFragment: Thread is main onCompletion

看下面的方法，将flowOn放在onStart、onEach后面

private fun flowOn() {
        lifecycleScope.launch {
            simpleFlowOn()
                .onStart {
                    LogUtils.d("Thread is ${Thread.currentThread().name} onStart")
                }
                .onEach {
                    LogUtils.d("Thread is ${Thread.currentThread().name} onEach")
                }
                .flowOn(Dispatchers.IO)
                .catch { exception ->
                    LogUtils.d("Thread is ${Thread.currentThread().name} exception $exception")
                }
                .onCompletion {
                    LogUtils.d("Thread is ${Thread.currentThread().name} onCompletion")
                }
                .collect {
                    LogUtils.d("Thread is ${Thread.currentThread().name} collect $it")
                }
        }
    }

打印如下，onStart，onEach方法执行都在子线程了：

	//onStart，onEach方法执行都在子线程了
    D/FlowFragment: Thread is DefaultDispatcher-worker-1 onStart
    D/FlowFragment: Thread is DefaultDispatcher-worker-1 Emitting 1
    D/FlowFragment: Thread is DefaultDispatcher-worker-1 onEach
    D/Collect: Thread is main collect 1
    D/FlowFragment: Thread is DefaultDispatcher-worker-1 Emitting 2
    D/FlowFragment: Thread is DefaultDispatcher-worker-1 onEach
    D/Collect: Thread is main collect 2
    D/FlowFragment: Thread is DefaultDispatcher-worker-1 Emitting 3
    D/FlowFragment: Thread is DefaultDispatcher-worker-1 onEach
    D/Collect: Thread is main collect 3
    D/FlowFragment: Thread is main onCompletion