The difference between invalidate and Postinvalidate in Android

There are two sets of methods for implementing view updates in Android, one for invalidate. There is also a group of postinvalidate. The former is in the UI line


The process itself, while the latter is used in a non-UI thread.

Android provides the Invalidate method for UI refresh. However, invalidate cannot be called directly in the thread. As he was against the single


Threading Model: Android UI operations are not thread-safe, and these operations must be called in the UI thread.

There are two kinds of interface refresh methods that can be used in Android programs. Each uses handler and uses postinvalidate () to achieve


Refreshes the interface in the thread.


1, using invalidate () to refresh the interface
Instantiate a handler object and override the Handlemessage method call invalidate () to implement the interface refresh, while the thread passes through the


SendMessage Send interface update message.

To open a thread in OnCreate ()




New Thread (New Gamethread ()). Start ();


Instantiate a handler


Handler MyHandler = new Handler () {
Receive Message post processing
public void Handlemessage (Message msg) {
Switch (msg.what) {
Case Activity01.refresh:
Mgameview.invalidate (); Refresh Interface
Break
}


Super.handlemessage (msg);
}
};


Class Gamethread implements Runnable {
public void Run () {
while (! Thread.CurrentThread (). isinterrupted ()) {
Message message = new Message ();
Message.what = Activity01.refresh;
Send Message
Activity01.this.myHandler.sendMessage (message);
try {
Thread.Sleep (100);
} catch (Interruptedexception e) {
Thread.CurrentThread (). interrupt ();
}
}
}
}


2, use Postinvalidate () to refresh the interface
The use of postinvalidate is relatively simple, do not need to handler, directly in the thread call Postinvalidate can be.


Class Gamethread implements Runnable {
public void Run () {
while (! Thread.CurrentThread (). isinterrupted ()) {
try {
Thread.Sleep (100);
} catch (Interruptedexception e) {
Thread.CurrentThread (). interrupt ();
}


Use Postinvalidate to update the interface directly in the thread
Mgameview.postinvalidate ();
}
}
}

The Postinvalidate () method in the View class source code such as the following, can be seen that it is also used in the handler:
public void Postinvalidate () {
postinvalidatedelayed (0);
}


public void postinvalidatedelayed (long delaymilliseconds) {
We try only with the attachinfo because there's no point in invalidating
If we is not a attached to our window
if (mattachinfo! = null) {
Message msg = Message.obtain ();
Msg.what = attachinfo.invalidate_msg;
Msg.obj = this;
MAttachInfo.mHandler.sendMessageDelayed (msg, delaymilliseconds);
}
}


In addition to OnCreate () is executed on the UI thread, the fact that most of the other methods are executed on the UI thread, in fact, you just don't have


Open a new thread, and your code is basically executed on the UI thread.

The difference between invalidate and Postinvalidate in Android