[英]Stop and Start a thread Android
我正在尝试一个EditText,它会随着经过的时间不断更新。 这是由线程处理的,该线程调用一种方法来计算经过时间并将EditText文本设置为经过时间。 线程每秒休眠一次。 该线程在用户按下“开始”时启动,并在用户按下“停止”时停止。 当用户再次按下“开始”时,线程应从0重新开始(因为重新设置了开始时间)。 这是代码:
public class MainActivity extends AppCompatActivity {
public Date start;
public Date end;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button startButton = (Button) findViewById(R.id.startButton);
Button endButton = (Button) findViewById(R.id.stopButton);
final EditText dateEditText = (EditText) findViewById(R.id.dateEditText) ;
final EditText hoursEditText = (EditText) findViewById(R.id.hoursEditText); //the one I want to update
final DateFormat df = new SimpleDateFormat("MM/dd/yy");
final Thread t = new Thread() {
@Override
public void run() {
try {
while (!isInterrupted()) {
Thread.sleep(1000);
runOnUiThread(new Runnable() {
@Override
public void run() {
setTimeElapsed(hoursEditText);
}
});
}
} catch (InterruptedException e) {
}
}
};
startButton.setOnClickListener(new View.OnClickListener(){
public void onClick(View v){
start = new Date();
dateEditText.setText(df.format(start));
hoursEditText.setText("");
t.start();
}
});
endButton.setOnClickListener(new View.OnClickListener(){
public void onClick(View v){
t.interrupt();
if (start == null) {
//write error message
}
else {
setTimeElapsed(hoursEditText);
start = null;
}
}
});
}
public void setTimeElapsed(EditText hoursEditText)
{
end = new Date();
long diff = end.getTime() - start.getTime();
String diffFormatted = String.format("%02d:%02d:%02d",
TimeUnit.MILLISECONDS.toHours(diff),
TimeUnit.MILLISECONDS.toMinutes(diff)
- TimeUnit.HOURS.toMinutes(TimeUnit.MILLISECONDS.toHours(diff)),
TimeUnit.MILLISECONDS.toSeconds(diff)
- TimeUnit.MINUTES.toSeconds(TimeUnit.MILLISECONDS.toMinutes(diff)));
hoursEditText.setText(diffFormatted);
}
}
如您所见,问题在于当我按下“停止”然后再次按下“启动”时,该应用程序将引发错误,因为该线程已经在运行。 如果我没有interrupt语句,则该应用程序崩溃,因为它认为start
为null。 我只想在按下停止按钮时停止线程,并在按下开始按钮时从0开始计数。
编辑:
解决这个问题的一种方法是拥有一个创建新线程的方法,并在我的startButton
侦听器中调用该方法
public void startThread(final EditText hoursEditText){
t = new Thread() {
@Override
public void run() {
try {
while (!isInterrupted()) {
Thread.sleep(1000);
runOnUiThread(new Runnable() {
@Override
public void run() {
setTimeElapsed(hoursEditText);
}
});
}
} catch (InterruptedException e) {
}
}
};
t.start();
}
但这每次有人按下开始都会创建一个新线程。 这不好。
您可以使用处理程序
Handler handler = new Handler();
final Thread thread = new Thread(new Runnable() {
@Override
public void run() {
setTimeElapsed(hoursEditText);
handler.postDelayed(this, 100);
}
});
//在结束按钮上单击,您可以删除处理程序回调
endButton.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
if(handler != null)
handler.removeCallbacksAndMessages(null);
}
});
完整的代码
import android.os.Bundle;
import android.os.Handler;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.concurrent.TimeUnit;
public class MainActivity extends AppCompatActivity {
public Date start;
public Date end;
Handler handler = new Handler();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button startButton = (Button) findViewById(R.id.startButton);
Button endButton = (Button) findViewById(R.id.stopButton);
final EditText dateEditText = (EditText) findViewById(R.id.dateEditText);
final EditText hoursEditText = (EditText) findViewById(R.id.hoursEditText); //the one I want to update
final DateFormat df = new SimpleDateFormat("MM/dd/yy");
final Thread thread = new Thread(new Runnable() {
@Override
public void run() {
setTimeElapsed(hoursEditText);
handler.postDelayed(this, 100);
}
});
startButton.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
start = new Date();
dateEditText.setText(df.format(start));
hoursEditText.setText("");
handler.post(thread);
}
});
endButton.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
if(handler != null)
handler.removeCallbacksAndMessages(null);
}
});
}
public void setTimeElapsed(EditText hoursEditText) {
end = new Date();
long diff = end.getTime() - start.getTime();
String diffFormatted = String.format("%02d:%02d:%02d",
TimeUnit.MILLISECONDS.toHours(diff),
TimeUnit.MILLISECONDS.toMinutes(diff)
- TimeUnit.HOURS.toMinutes(TimeUnit.MILLISECONDS.toHours(diff)),
TimeUnit.MILLISECONDS.toSeconds(diff)
- TimeUnit.MINUTES.toSeconds(TimeUnit.MILLISECONDS.toMinutes(diff)));
hoursEditText.setText(diffFormatted);
}
}
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