Android線程間通訊

Android採用UI單執行緒模式，所以背景工作執行緒（非UI線程）與UI線程的通訊是不可避免的。背景工作執行緒與UI主線程通訊（進行更新UI等操作）主要有以下三種方式。

First :

Looper.getMainLooper()

Runnable task = getTask();

new Handler(Looper.getMainLooper()).post(task);

Second :

Activity#runOnUiThread()

Runnable task = getTask();

runOnUiThread(task);

The implements of runOnUiThread is shown as bellow :

public final void runOnUiThread(Runnable action) {
if (Thread.currentThread() != mUiThread) {
mHandler.post(action);
} else {
action.run();
}
}
It will check if the current Thread is already the UI thread and then execute it directly. Posting it as a message will delay the execution until you return from the current UI-thread method.

Third：

There is also a third way to execute a Runnable on the UI thread which would be View#post(Runnable) - this one will always post the message even when called from the UI thread. That is useful since that will ensure that the View has been properly constructed and has a layout before the code is executed.