轉 android開發筆記之handler+Runnable的一個巧妙應用
1. 一個有趣Demo:
(1)定義一個handler變數
private final Handler mHandler = new Handler();
(2)定義一個Runnable變數
private Runnable onDoSomethingRunnable = new Runnable() {
public void run() {
onDoSomething();
}
};
(3)定義onDoSomething()方法:
public void onDoSomething(){
..................................
..................................
mHandler.postDelayed(onDoSomethingRunnable,150);
}
大家看一下上面的程式碼,發現了什麼沒。對,這個組合,可以實現每隔一段時間,迴圈的執行某個操作。eg:每隔一秒,更新UI,每隔一段時間,去檢視一個程序或者服務是否結束,............等等.當然了,大家可能會發現,一種方式可能有點消耗資源,因為他會迴圈的執行固定的操作,所以一般還是少用。
2. 一些關於Handler的事情:
A Handler allows you to send and process Message and Runnable objects associated with athread's MessageQueue
handler的作用,我就不說了,這種機制,我的理解是將一些非主UI執行緒更新UI,傳遞一些資料等等。當然,官方的說明:
There are two main uses for a Handler: (1) to schedulemessagesandrunnablesto beexecuted as some point in the future; and (2) to enqueue anaction
Handler中分發訊息和runnable的一些方法:
post(Runnable),postAtTime(Runnable, long),postDelayed(Runnable, long),
sendEmptyMessage(int),sendMessage(Message),sendMessageAtTime(Message, long),sendMessageDelayed(Message, long)
Handler刪除訊息和runnable的方法:
removeCallbacks(Runnable),removeCallbacks(Runnable, Object ),removeCallbacksAndMessages(Object),
removeMessages(int), removeMessages(int , Object )
3.幾個經典的DEMO。
(1)在一段資料處理的耗時操作後,如果這個操作超過1s,就顯示進度條,如果耗時操作不超過1s,則不顯示進度條後
//Handler處理訊息
final Handler handler = new Handler();
final ProgressDialog progressDialog = new ProgressDialog(this);
progressDialog.setMessage(getText(R.string.adding_recipients));
progressDialog.setIndeterminate(true);
progressDialog.setCancelable(false);
final Runnable showProgress = new Runnable() {
public void run() {
progressDialog.show();
}
};
// Only show the progress dialog if we can not finish off parsing the return data in 1s,
// otherwise the dialog could flicker.
handler.postDelayed(showProgress, 1000);
new Thread(new Runnable() {
public void run() {
try {
//資料處理
} finally {
handler.removeCallbacks(showProgress);
progressDialog.dismiss();
}
}
}).start();
(2)更新UI介面
在需要更新頁面的地方,發出更新介面的命令
private static final int UPDATE_PAGE_INDICATOR = 1;
/****更新使用者選中的數目******/
private static final int UPDATE_SELE_COUNT = 2;
/****更新頁面指示器******/
Message msg = myHandler.obtainMessage();
Bundle bundle = new Bundle();
//bundle.putInt("page", page);
bundle.putInt("page", PageCurrent);
msg.setData(bundle); // 向訊息中新增資料
msg.what = UPDATE_PAGE_INDICATOR;
myHandler.sendMessage(msg); // 向Handler傳送訊息,更新UI
在需要更新指示選中數目的TextView的地方,發出更新介面的命令
myHandler.sendEmptyMessage(UPDATE_SELE_COUNT);
更新介面的操作,都放在myHandler 中
/***********myHandler:更新介面***********/
public Handler myHandler = new Handler(){
public void handleMessage(Message msg) {
super.handleMessage(msg);
switch(msg.what)
{
case UPDATE_PAGE_INDICATOR :
Bundle data = msg.getData();
int page = (Integer) data.get("page");
/*****更新頁面指示器******/
upDatePageIndicator(page);
break;
case UPDATE_SELE_COUNT:
mySelectCount.setText(""+selectCount);
break;
}
}
};
(3).Handler 和 Runnable 控制顯示一個文字,1.5s後,讓其不顯示:
private TextView overlay = null;
LayoutInflater inflater = LayoutInflater.from(this);
overlay = (TextView) inflater.inflate(R.layout.overlay, null);
private Handler <strong>handler</strong>;
handler = new Handler();
private OverlayThread <strong>overlayThread</strong>;
overlayThread = new OverlayThread();
overlay.setText(sections[position]);
overlay.setVisibility(View.VISIBLE);
<strong>handler.removeCallbacks(overlayThread);
/*****延遲一秒後執行,讓overlay為不可見*****/
handler.postDelayed(overlayThread, 1500);</strong>
/**
* 類描述:OverlayThread:實現設定overlay不可見
* @author hexiaoming
* @version
*/
private class OverlayThread implements Runnable {
/**
* 方法描述:run方法
* @param
* @return
* @see OverlayThread
*/
public void run() {
overlay.setVisibility(View.GONE);
}
}
參考資料:
1.Android的Handler總結
http://www.cnblogs.com/dawei/archive/2011/04/09/2010259.html