Using the handler class to update the UI

In Android, we often have to go online to get some data, and then update the UI, but it takes time to get the data, if the main thread directly using the code to get the data. The entire activity will be stuck there until you get to the end of the data update UI before the load is complete. In Android, if an activity card is 5 seconds away, it will be forcibly reclaimed.

Think back to the app we used, when it comes to loading, what's the general? Certainly will not let the interface card die there, the most incompetent also has a "load in" the circle in that turn! Then the data is loaded and disappears.

However, Android has a very subtle mechanism, the update UI can only be in the UI thread, that is, in our main thread, and access to the network only in other threads, what to do? The answer is to use the handler class.

The main idea is like this:

1, let the program start with a "load in" the Circle (Dialog).

2, handler is instantiated in the main thread, belongs to the main thread.

3, in the main thread to open another threads, used to access the Network load data, after loading, send a message to the handler class.

4, Handler received the message, update the UI, and then cancel the "load in" the circle.

Suppose a situation: to access the network, find a sentence, and then update our TextView

 　　　　 PrivateHandler Handler;//Statement Hanler 　　 PrivateTextviwe TV;//Statement TextView 　　　　 protected voidonCreate (Bundle savedinstancestate) {Super. OnCreate (savedinstancestate);　Setcontentview (R.layout.activity_first_page); //instantiating handler in the main threadHandler =NewHandler () {@Override//What to do when you receive a message     Public voidhandlemessage (Message msg) {Super. Handlemessage (msg); //Update TextView UI//cancel the "load in" boxDialog.cancel (); }};//Create a window to wait for the loadDialog =NewProgressDialog ( This);d Ialog.setmessage ("Data Initialization ...");d ialog.setcancelable (false);d Ialog.setcanceledontouchoutside (false);d ialog.show ();//open a new thread to access the network, get the dataNewThread (NewRunnable () {@Override Public voidrun () {//Access Network//send a message to handlerMessage OK =NewMessage ();    Handler.sendmessage (OK); }}). Start ();}//End OnCreate 　　 

Briefly describe the order in which the activity is run: When you start the app, the activity will make all the statements, instantiation, layout, and so on. And then into the Dialog.show (), this place, and then the entire interface is a circle around the turn ah. At the same time, a thread is opened to access the network. Instantly a thread is spinning and turning (Dialog), another thread accesses the network, obtains data, and does not interfere with each other. When the data is finished, a message class is instantiated and the message is sent to handler. Handler after receiving the message, update the UI, then Dialog.cancel () and cancel the loop. And then what we see is the updated interface.

The above just, concise code and verbal language, should also be more understandable.

　　

Using the handler class to update the UI