在開發中我們經常會遇到在子線程中更新ui的操作,那我們今天就介紹下幾種常用的方式
1.使用 runOnUiThread方法更新ui
2.view.post 方法
3.view.postDelaged 方法
4.handler.send...方法更新ui
1.使用 runOnUiThread方法更新ui
這個方法在Activity 中 ,所以只有在他的子類或者拿到他實例時才能使用
runOnUiThread(new Runnable() {
@Override
public void run() {
}
});
我們看下runOnUiThread方法的源碼
public final void runOnUiThread(Runnable action) {
if (Thread.currentThread() != mUiThread) {
mHandler.post(action);
} else {
action.run();
}
}
這裏有個判斷,如果是當前的ui線程那麼就直接執行runnable 的run方法開始更新ui,如果不是就用handler發送posp 消息,我們先看下mHandler是咋回事,通過activity源碼發現它本身new了一個mHandler 就是我們剛纔使用的handrler,如果你瞭解過handrler 源碼你就知道,handrler是會去綁定一個Looper,android應用在啓動的時候就創建了looper 並且開始輪詢,具體看ActiityThead main方法
public static void main(String[] args) {
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "ActivityThreadMain");
SamplingProfilerIntegration.start();
// CloseGuard defaults to true and can be quite spammy. We
// disable it here, but selectively enable it later (via
// StrictMode) on debug builds, but using DropBox, not logs.
CloseGuard.setEnabled(false);
Environment.initForCurrentUser();
// Set the reporter for event logging in libcore
EventLogger.setReporter(new EventLoggingReporter());
// Make sure TrustedCertificateStore looks in the right place for CA certificates
final File configDir = Environment.getUserConfigDirectory(UserHandle.myUserId());
TrustedCertificateStore.setDefaultUserDirectory(configDir);
Process.setArgV0("<pre-initialized>");
//獲取主線程的looper對象
Looper.prepareMainLooper();
//開啓主線程
ActivityThread thread = new ActivityThread();
thread.attach(false);
if (sMainThreadHandler == null) {
sMainThreadHandler = thread.getHandler();
}
if (false) {
Looper.myLooper().setMessageLogging(new
LogPrinter(Log.DEBUG, "ActivityThread"));
}
// End of event ActivityThreadMain.
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
//開始消息輪訓
Looper.loop();
throw new RuntimeException("Main thread loop unexpectedly exited");
}
到這裏我們知道主線程已將存在, looper已經創建完畢,並開始輪詢消息。現在處於主線程中handler綁定主線程中的looper。瞭解完這些,我們心中大概有個概念了。那繼續看下post方法
public final boolean post(Runnable r)
{
return sendMessageDelayed(getPostMessage(r), 0);
}
private static Message getPostMessage(Runnable r) {
Message m = Message.obtain();
m.callback = r;
return m;
}
看到傳進來的Runnable 方法賦值給了 一條消息的callback 接口,然後調用sendMessagDelayed方法,這個方法我們應該比較熟悉了,不就是我們平時使用handler發送消息時調用的方法麼。這個方法最會調用到了sendMessageAtFrontOfQueue(Message msg) 方法,這個比較重要了。
public final boolean sendMessageAtFrontOfQueue(Message msg) {
MessageQueue queue = mQueue;
if (queue == null) {
RuntimeException e = new RuntimeException(
this + " sendMessageAtTime() called with no mQueue");
Log.w("Looper", e.getMessage(), e);
return false;
}
return enqueueMessage(queue, msg, 0);
}
首先拿到了當前線程也就是主線程的消息隊列mQueue,如果不知咋回事建議看看下handler原理,這裏就再嘮叨幾句,一個線程中會有一個looper 對象和一個MessageQueue對象 可以有多個handler 。然後調用了enqueueMessage(MessageQueue queue, Message msg, long uptimeMillis) 方法 。
private boolean enqueueMessage(MessageQueue queue, Message msg, long uptimeMillis) {
msg.target = this;
if (mAsynchronous) {
msg.setAsynchronous(true);
}
return queue.enqueueMessage(msg, uptimeMillis);
}
然後調用消息隊列的enqueueMessage 將消息放入消息對列中
boolean enqueueMessage(Message msg, long when) {
if (msg.target == null) {
throw new IllegalArgumentException("Message must have a target.");
}
if (msg.isInUse()) {
throw new IllegalStateException(msg + " This message is already in use.");
}
synchronized (this) {
if (mQuitting) {
IllegalStateException e = new IllegalStateException(
msg.target + " sending message to a Handler on a dead thread");
Log.w(TAG, e.getMessage(), e);
msg.recycle();
return false;
}
msg.markInUse();
msg.when = when;
Message p = mMessages;
boolean needWake;
//把剛進入消息隊列的消息置位消息隊列的第一條消息
if (p == null || when == 0 || when < p.when) {
// New head, wake up the event queue if blocked.
msg.next = p;
mMessages = msg;
needWake = mBlocked;
} else {
//根據時間排序,爲剛進入隊列的消息尋找合適的位置
// Inserted within the middle of the queue. Usually we don't have to wake
// up the event queue unless there is a barrier at the head of the queue
// and the message is the earliest asynchronous message in the queue.
needWake = mBlocked && p.target == null && msg.isAsynchronous();
Message prev;
for (;;) {
prev = p;
p = p.next;
if (p == null || when < p.when) {
break;
}
if (needWake && p.isAsynchronous()) {
needWake = false;
}
}
msg.next = p; // invariant: p == prev.next
prev.next = msg;
}
// We can assume mPtr != 0 because mQuitting is false.
if (needWake) {
nativeWake(mPtr);
}
}
return true;
}
- 第一種情況比較好理解,就是把當前消息的next 指向一個空消息 將自身賦值爲mMessages的值
- 重點理解下第二種情況,假設有三條消息,三條消息對應的when值分別爲3,5,9
- 假設我們傳進來的msg的when值爲 4,那初次進入參數值爲
1. prev.when=p.when=3
2. p.when=p.next.when= 5
3. xxMessage.when= 9
現在msg.when的值小於p.when=5 ,when<p.when 所以執行了 break方法,那麼msg.next=p 既msg的下一條指向了p,
prev.next=msg 既 prev --> msg--->p---->xxMessage 順利將msg插入到隊列中。
接着我們看下消息的出列操作,前邊我們講過Looper對象, ui線已經創建了looper對象 和隊列 並且調用了Looper.loop()方法開始輪詢消息出站操作。看下loop()方法。
public static void loop() {
//獲取looper對象
final Looper me = myLooper();
if (me == null) {
throw new RuntimeException("No Looper; Looper.prepare() wasn't called on this thread.");
}
//拿到了隊列
final MessageQueue queue = me.mQueue;
// Make sure the identity of this thread is that of the local process,
// and keep track of what that identity token actually is.
Binder.clearCallingIdentity();
final long ident = Binder.clearCallingIdentity();
//無限循環取消息
for (;;) {
//獲取when值最小的一條消息
Message msg = queue.next(); // might block
if (msg == null) {
// No message indicates that the message queue is quitting.
return;
}
// This must be in a local variable, in case a UI event sets the logger
final Printer logging = me.mLogging;
if (logging != null) {
logging.println(">>>>> Dispatching to " + msg.target + " " +
msg.callback + ": " + msg.what);
}
final long slowDispatchThresholdMs = me.mSlowDispatchThresholdMs;
final long traceTag = me.mTraceTag;
if (traceTag != 0 && Trace.isTagEnabled(traceTag)) {
Trace.traceBegin(traceTag, msg.target.getTraceName(msg));
}
final long start = (slowDispatchThresholdMs == 0) ? 0 : SystemClock.uptimeMillis();
final long end;
try {
//獲取當前綁定的handler 並且調用其中的dispatchMessage方法,執行handler handlerMessage回調
msg.target.dispatchMessage(msg);
end = (slowDispatchThresholdMs == 0) ? 0 : SystemClock.uptimeMillis();
} finally {
if (traceTag != 0) {
Trace.traceEnd(traceTag);
}
}
if (slowDispatchThresholdMs > 0) {
final long time = end - start;
if (time > slowDispatchThresholdMs) {
Slog.w(TAG, "Dispatch took " + time + "ms on "
+ Thread.currentThread().getName() + ", h=" +
msg.target + " cb=" + msg.callback + " msg=" + msg.what);
}
}
if (logging != null) {
logging.println("<<<<< Finished to " + msg.target + " " + msg.callback);
}
// Make sure that during the course of dispatching the
// identity of the thread wasn't corrupted.
final long newIdent = Binder.clearCallingIdentity();
if (ident != newIdent) {
Log.wtf(TAG, "Thread identity changed from 0x"
+ Long.toHexString(ident) + " to 0x"
+ Long.toHexString(newIdent) + " while dispatching to "
+ msg.target.getClass().getName() + " "
+ msg.callback + " what=" + msg.what);
}
//將當前message 初始化以便重複利用
msg.recycleUnchecked();
}
}
這裏主要有三個點注意,1.隊列是如何獲取when最小的一條消息,2.message是如何重複利用的 這兩個我們今天不做探討,我們主要看下 3.run 方法是如何執行或者handlerMessage如何執行的。進入handler 的dispatchMessage方法看下。
public void dispatchMessage(Message msg) {
if (msg.callback != null) {
handleCallback(msg);
} else {
if (mCallback != null) {
if (mCallback.handleMessage(msg)) {
return;
}
}
handleMessage(msg);
}
}
代碼一目瞭然,如果message設置了callback 那麼執行handlerCallback 方法,否則執行我們熟悉的handlerMesage方法。
這段我們講的是runOnUiThread 傳進來一個接口並且獲取到了Message對象 when賦值爲0 ,msg.callback =Runnable(傳入的接口)
看下handleCallback(Message message) 方法。
private static void handleCallback(Message message) {
message.callback.run();
}
只有一行代碼,那就是執行run方法。走了這麼大一圈,終於完了。
總結下從runOnUiThread 到run方法執行過程:首先runOnUiThread 方法傳入了一個接口,然後獲取一個message對象,獲取主線程的looper,對列,和handler,然後是消息的入棧操作,接着是消息出棧,獲取當前消息的handler調用消息分發事件dispatchMessage,然後判斷是接口爲空,不爲空的話執行run方法。
2.view.post 方法
接着看下post方法,上面講了那麼多,如果都理解了,下面的相對就非常簡單了。
mPhotoView.post(new Runnable() {
@Override
public void run() {
}
});
這個和 runOnUiThread 基本類似,都是傳入一個Runnable接口,看下post(Runnable action)方法。
public boolean post(Runnable action) {
final AttachInfo attachInfo = mAttachInfo;
if (attachInfo != null) {
return attachInfo.mHandler.post(action);
}
// Postpone the runnable until we know on which thread it needs to run.
// Assume that the runnable will be successfully placed after attach.
getRunQueue().post(action);
return true;
}
attachinfo 是當前view 的屬性信息,如果爲空調用隊列的post方法。
attachInfo.mHandler.post(action) 這個是view 本身都會有一個handler 綁定的是主線程的looper ,再看post
public final boolean post(Runnable r)
{
return sendMessageDelayed(getPostMessage(r), 0);
}
調用到了handler 的sendMessageDelayed(Message msg,long delayMillis)方法我們上邊講過了,接下來他的調用流程和runOnUiThread 一樣了。最後都會執行run方法。
現在看下attactInfo 爲空的情況。
getRunQueue().post(action);
看下RunQueue是啥
static RunQueue getRunQueue() {
RunQueue rq = sRunQueues.get();
if (rq != null) {
return rq;
}
rq = new RunQueue();
sRunQueues.set(rq);
return rq;
}
先通過aRunQueues.get獲取一個Runqueue對象,如果有就返回,沒有就新建一個並調用sRunQueues的set方法,這個不細說,重點看下RunQueue 的post
void post(Runnable action) {
postDelayed(action, 0);
}
void postDelayed(Runnable action, long delayMillis) {
HandlerAction handlerAction = new HandlerAction();
handlerAction.action = action;
handlerAction.delay = delayMillis;
synchronized (mActions) {
mActions.add(handlerAction);
}
}
其實 是調用了postDelayed方法,我們看到新建了一個HandlerActivity 並且初始化參數, 並加入到一個 ArrayList 集合中。那他在哪裏取出hadlerAction 呢。
void executeActions(Handler handler) {
synchronized (mActions) {
final ArrayList<HandlerAction> actions = mActions;
final int count = actions.size();
for (int i = 0; i < count; i++) {
final HandlerAction handlerAction = actions.get(i);
handler.postDelayed(handlerAction.action, handlerAction.delay);
}
actions.clear();
}
}
在當前類中有這麼一個方法,取出了handlerAction 並且調用了handler的postDelayed方法,這個我們比較熟悉,就是最後要執行run方法了。我們重點看下executeAction 何時調用的。在ViewRootlmp 中找到了。performTraversals方法,那麼它又是哪裏調用的呢。
向上追溯, doTraversal() ---> TraversalRunnable ---> scheduleTraversals 最後到了這裏,這個方法是繪製view了
boolean cancelDraw = mAttachInfo.mTreeObserver.dispatchOnPreDraw() ||
viewVisibility != View.VISIBLE;
if (!cancelDraw && !newSurface) {
if (!skipDraw || mReportNextDraw) {
if (mPendingTransitions != null && mPendingTransitions.size() > 0) {
for (int i = 0; i < mPendingTransitions.size(); ++i) {
mPendingTransitions.get(i).startChangingAnimations();
}
mPendingTransitions.clear();
}
performDraw();
}
} else {
if (viewVisibility == View.VISIBLE) {
// Try again
scheduleTraversals();
} else if (mPendingTransitions != null && mPendingTransitions.size() > 0) {
for (int i = 0; i < mPendingTransitions.size(); ++i) {
mPendingTransitions.get(i).endChangingAnimations();
}
mPendingTransitions.clear();
}
}
說實話,這個方法調用的地方太多了,一時間還真的難以確認是哪裏調用的,只能大膽猜測下,在view 屬性獲取成功,並且狀態可見時調用。現在算是流程整個通了,梳理下:當沒有獲取到view相關屬性時,就將action存起來(mActions.add(handlerAction)),等到獲取到view相關屬性並且狀態可見時再取出(scheduleTraversals)。
現在看executeActions(方法)調用了handler的postDelayed方法 ,當然,這個handler也是主線程的,下面流程就是handler那套了,通過判斷是否有接口,執行run方法。
3.view.postDelaged 方法
前面我們講了view.post 方法,如果你仔細觀察,這個方法其實都不用講了。
public boolean postDelayed(Runnable action, long delayMillis) {
final AttachInfo attachInfo = mAttachInfo;
if (attachInfo != null) {
return attachInfo.mHandler.postDelayed(action, delayMillis);
}
// Assume that post will succeed later
ViewRootImpl.getRunQueue().postDelayed(action, delayMillis);
return true;
}
其實分別調用了handrle的postDelayed 和RunQueue 的postDelayed 方法。而view.post只是對postDelayed的簡單封裝。
attachInfo.mHandler.post(action);
public final boolean post(Runnable r)
{
return sendMessageDelayed(getPostMessage(r), 0);
}
attachInfo.mHandler.post(action);
void post(Runnable action) {
postDelayed(action, 0);
}
其他的流程都一樣。
4.handler.send...方法更新ui
上面我們講了幾種更新更新ui的方式,其實歸根到底好是調用了handler的send...方法來更新數據。
但是歸根到底還是調用了 sendMessageAtTime(Message msg, long uptimeMillis) 方法。
public boolean sendMessageAtTime(Message msg, long uptimeMillis) {
MessageQueue queue = mQueue;
if (queue == null) {
RuntimeException e = new RuntimeException(
this + " sendMessageAtTime() called with no mQueue");
Log.w("Looper", e.getMessage(), e);
return false;
}
return enqueueMessage(queue, msg, uptimeMillis);
}
最後通過enqueueMessage 將消息送入到消息隊列中,然後消息隊列輪行取出消息執行handler中的
public void dispatchMessage(Message msg) 方法,然後執行
private static void handleCallback(Message message) {
message.callback.run();
}
或者
handleMessage(msg)
方法,在run 中或在 handleMessage 執行我們的更新ui 的操做。
到這裏更新ui 的幾種方法就介紹完了,本來覺得一天就能搞定的結果搞了四天才寫完,其中又不斷的學習了新的知識,希望大家在看的時候儘量的結合源碼去看,這樣能夠更好的理解。
補充一點,在看資料的時候看到有人說IntentService 和AsyncTask 也可以更新ui 其實他們都是內置了一個子線程然後綁定了一個主線程的Handler實現的。
參考:
https://blog.csdn.net/suma_sun/article/details/51584026
https://blog.csdn.net/lufeng20/article/details/24314381
https://blog.csdn.net/qq_23547831/article/details/50751687