public class TestActivity extends Activity {
// ...
// all standard stuff
@Override
public void onCreate(Bundle savedInstanceState) {
// ...
// all standard stuff
// we're creating a new handler here
// and we're in the UI Thread (default)
// so this Handler is associated with the UI thread
Handler mHandler = new Handler();
// I want to start doing something really long
// which means I should run the fella in another thread.
// I do that by sending a message - in the form of another runnable object
// But first, I'm going to create a Runnable object or a message for this
Runnable mRunnableOnSeparateThread = new Runnable() {
@Override
public void run () {
// do some long operation
longOperation();
// After mRunnableOnSeparateThread is done with it's job,
// I need to tell the user that i'm done
// which means I need to send a message back to the UI thread
// who do we know that's associated with the UI thread?
mHandler.post(new Runnable(){
@Override
public void run(){
// do some UI related thing
// like update a progress bar or TextView
// ....
}
});
}
};
// Cool but I've not executed the mRunnableOnSeparateThread yet
// I've only defined the message to be sent
// When I execute it though, I want it to be in a different thread
// that was the whole point.
new Thread(mRunnableOnSeparateThread).start();
}
}
如果根本就没有Handler对象，回调post方法会比较难办。
示例2：使用postDelayed方法
近期本站新介绍的特性中，我每次都要模拟EditText的自动完成功能，每次文字改变后都会触发一个API的调用，从服务器中检索数据。
我想减少APP调用API的次数，所以决定使用Handler的postDelayed方法来实现这个功能。
本例不针对平行处理，只是关于Handler给消息队列发送消息还有安排消息在未来的某一点执行等。
// the below code is inside a TextWatcher
// which implements the onTextChanged method
// I've simplified it to only highlight the parts we're
// interested in
private long lastChange = 0;
@Override
public void onTextChanged(final CharSequence chars,
int start, int before, int count) {
// The handler is spawned from the UI thread
new Handler().postDelayed(
// argument 1 for postDelated = message to be sent
new Runnable() {
@Override
public void run() {
if (noChangeInText_InTheLastFewSeconds()) {
searchAndPopulateListView(chars.toString());
// logic
}
}
},
// argument 2 for postDelated = delay before execution
300);
lastChange = System.currentTimeMillis();
}
private boolean noChangeInText_InTheLastFewSeconds() {
return System.currentTimeMillis() - lastChange >= 300
}
