●程式說明--多重執行緒補充
=>run倒數計時
(一)conuntDownTimer=>非多重執行緒，是在主執行緒做
public class MainActivity extends AppCompatActivity {
TextView mTextField;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mTextField=(TextView)findViewById(R.id.mTextField);
//每秒鐘執行一次，總共執行30次CountDownTimer，都是在主執行緒執行
new CountDownTimer(30000, 1000) {
//倒數時要run的程式
public void onTick(long millisUntilFinished) {
mTextField.setText("seconds remaining: " + millisUntilFinished / 1000);
}
//結束後要run的程式
public void onFinish() {
mTextField.setText("done!");
}
}.start();
}
}
**說明：
1.CountDownTimer (long millisInFuture, long countDownInterval)
=>Parameters
millisInFuture long: The number of millis in the future from the call to start() until the countdown is done and onFinish() is called.
countDownInterval long: The interval along the way to receive onTick(long) callbacks.
=>問題：因為onTick和onFinsish都是在主執行緒上跑，如果在這兩個method中跑很花時間的程式，還是會讓程式卡住ex，如果再onTick中加入，就會跑一下跳過兩秒，29=>26=>23....程式被卡住了
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
(二)使用runOnUi
public void runonui(View view) {
new Thread(){
int i = 5;
@Override
public void run() {
super.run();
do {
runOnUiThread(new Runnable() {
@Override
public void run() {
tv2.setText(String.valueOf(i));
}
});
i--;
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
} while (i>=0);
}
}.start();
}
}
(三)使用Handler
public class MainActivity extends AppCompatActivity {
TextView tv3;
Handler handler;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
tv3=(TextView)findViewById(R.id.tv3);
handler=new Handler();
}
public void onhandler(View view) {
new Thread(){
int i = 5;
@Override
public void run() {
super.run();
do {
handler.post(new Runnable() {
@Override
public void run() {
tv3.setText(String.valueOf(i));
}
});
i--;
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
} while (i>0);
}
}.start();
}
}
**說明：
1.handler是android才有，java沒有的class
2.handler的method會在宣告handler的執行緒上run
3.這裡在主執行緒上宣告handler物件，在其他執行緒上用handler.post(~)，就會在主執行緒上執行post中的內容
4.實際上run的方法則是和runOnUi一樣，但使用上比較彈性，不限定只能在主執行緒上跑
(四)AsynTask=>處理執行緒和ui的機制，有六大function
=>因為是抽象類別而且有抽象方法，所以要繼承和override
=>繼承的時候，可以看到有三個泛型參數
1.執行 AsynTask要傳甚麼類型的資料(傳入的型別)
2.回報進度的型別
3.結果的型別(ex:如果是抓網路文字資料就是字串，如果是抓網路圖片就是bitmap)
.png)
//建立一個內部類別繼承AsynTask
class MyAsynTask extends AsyncTask<Integer,Integer,String>{
//因為要使用MainActivity的tv4但是不要設定static，就利用建構式把tv4傳進來
TextView tv;
public MyAsynTask(TextView tv){
this.tv=tv;
}
//override doInBackground方法=>在背景執行
//這邊的參數類型會和繼承時決定的傳入型別一樣，...是參數列表與陣列類似，可以一個或多個參數
//ex:abc(int [ ] x):void; 或 abc(int... x):void;
@Override
protected String doInBackground(Integer... integers) {
int n = integers[0];
int i;
for(i=n;i>=0;i--)
{
Log.d("TASK", "i:" + i);
//publishProgress(Progress... values): to publish updates on the UI thread while the background computation is still running
//參數:values Progress: The progress values to update the UI with.
publishProgress(i);
try {
Thread.sleep(500);
} catch (InterruptedException e) {
e.printStackTrace();
}
//Returns true if this task was cancelled before it completed normally
if (this.isCancelled() == true)
{
break;
}
}
return "OK";
}
@Override
//在執行之後
//會在doInBackground執行完之後才執行，而且是在主執行緒執行，並且doInBackground return的內容會丟到這邊的參數帶入
//所以看log這邊會顯示ok
protected void onPostExecute(String s) {
super.onPostExecute(s);
Log.d("TASK", s);
}
@Override
//進度更新，也是在主執行緒跑
//這邊的Integer...values是MyAsynTask<>第二個帶入的參數類型，由publishProgerss()傳值過來
//必須在 doInBackground加上publishProgress();
protected void onProgressUpdate(Integer... values) {
super.onProgressUpdate(values);
tv.setText(String.valueOf(values[0]));
}
@Override //當呼叫cancel method，會run onCancelled()
/*onCancelled
Applications should preferably override onCancelled(Object). This method is invoked by the default implementation of onCancelled(Object).
Runs on the UI thread after cancel(boolean) is invoked and doInBackground(Object[]) has finished.*/
protected void onCancelled() {
super.onCancelled();
}
}
●程式參考(GitHub)：多重執行續的補充說明(CountDownTimer、Handler、runOnUiThread、AsynTask)
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