用时钟更新 TextView

Question

我一直在尝试创建一个程序，该程序将输出一个可以工作的数字时钟，让我可以快速访问日期和时间。我有解析时间的代码，但是，我在更新 textview 时遇到了困难。我有这个：

    `public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    timer = (TextView)findViewById(R.id.timer);

    time = new Time();
    time.setToNow();

    timeString = time.toString();
    changeTime = Parser(timeString);


    time.setToNow();
    timeString = time.toString();
    changeTime = Parser(timeString);

    timer.setText(changeTime);  
    } 
    private String Parser(String time){

    String year = time.substring(0, 4);
    String month = time.substring(4,6);
    String day = time.substring(6, 8);
    String hour = time.substring(9,11);
    String minute = time.substring(11, 13);
    String second = time.substring(13, 15);

    String finalTime = hour + ":" + minute + ":" + second + " " + day + " " + month + " "  + year;
    //String finalTime = second;
    return finalTime;


}`

如何将其放入循环中以不断更新文本视图。

感谢您能给我的任何帮助。

Answer 1

使用永无止境的处理程序消息开始更新视图是一种不好的做法（尝试查看进程的 CPU 级别）。 更好更优雅的方法是注册一个BroadcastReceiver，它会触发更新。

public class Clock extends LinearLayout {

    private Calendar mCalendar;
    private LinearLayout mLayoutTime;
    private TextView mAMPMText;
    private TextView mDateText;
    private TextView mTimeText;
    private View mSendFeedback;
    private boolean mAttached;

    private final Handler mHandler = new Handler();
    SimpleDateFormat dateFormatter = new SimpleDateFormat("EEE, MMM d, yyyy");
    SimpleDateFormat timeFormatter = new SimpleDateFormat("h:mm");

    public Clock(final Context context, int layoutResourceID, int dateResId, int meResId,int amPmResId) {
        super(context);
        LayoutInflater layoutInflater = LayoutInflater.from(context);
        View view = layoutInflater.inflate(layoutResourceID, null);
        addView(view, new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT));
        mAMPMText = (TextView) view.findViewById(amPmResId);
        mTimeText = (TextView) view.findViewById(timeResId);
        mDateText = (TextView) view.findViewById(dateResId);    
    }

    @Override
    protected void onAttachedToWindow() {
        super.onAttachedToWindow();

        if (!mAttached) {
            mAttached = true;
            IntentFilter filter = new IntentFilter();

            filter.addAction(Intent.ACTION_TIME_TICK);
            filter.addAction(Intent.ACTION_TIME_CHANGED);
            filter.addAction(Intent.ACTION_TIMEZONE_CHANGED);

            getContext().registerReceiver(mIntentReceiver, filter, null, mHandler);
        }

        // NOTE: It's safe to do these after registering the receiver since the receiver always runs
        // in the main thread, therefore the receiver can't run before this method returns.

        // The time zone may have changed while the receiver wasn't registered, so update the Time
        mCalendar = Calendar.getInstance();

        // Make sure we update to the current time
        onTimeChanged();
        updateView();
    }

    @Override
    protected void onDetachedFromWindow() {
        super.onDetachedFromWindow();
        if (mAttached) {
            getContext().unregisterReceiver(mIntentReceiver);
            mAttached = false;
        }
    }

    private void updateView(){
        mTimeText.setText(timeFormatter.format(mCalendar.getTime()));
        mDateText.setText(dateFormatter.format(mCalendar.getTime()));
        mAMPMText.setText(mCalendar.get(Calendar.AM_PM) == 0 ? "AM" : "PM");
    }

    private void onTimeChanged() {
        mCalendar.setTime(new Date());

        updateContentDescription(mCalendar);
    }

    private final BroadcastReceiver mIntentReceiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            if (intent.getAction().equals(Intent.ACTION_TIMEZONE_CHANGED)) {
                String tz = intent.getStringExtra("time-zone");
                mCalendar.setTimeZone(TimeZone.getTimeZone(tz));
            }

            onTimeChanged();

            updateView();
        }
    };

    private void updateContentDescription(Calendar calendar) {
        setContentDescription(calendar.toString());
    }
}

布局（可以做得更好）

    <?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content"
    android:layout_height="match_parent"
    android:gravity="center_vertical"
    android:orientation="horizontal" >

    <LinearLayout
        android:id="@+id/layout_time"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="horizontal" >

        <TextView
            android:id="@+id/time_txt"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:includeFontPadding="true" />

        <TextView
            android:id="@+id/am_pm_txt"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="AM" />
    </LinearLayout>

    <TextView
        android:id="@+id/date_txt"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

</RelativeLayout>

Answer 2

您应该使用计时器线程。您还可以使用Calendar 简化您的时间和日期转换，并可以使用format 优化您的字符串创建。此示例将每秒（1000 毫秒）更新您的 TextView：

Timer t = new Timer();
timer = (TextView)findViewById(R.id.timer);

t.scheduleAtFixedRate(new TimerTask() 
{
    @Override
    public void run() {
        Calendar c = Calendar.getInstance();
        final String finalTime = String.format(Locale.US, "%d:%d:%d %d/%d/%d", c.get(Calendar.HOUR), c.get(Calendar.MINUTE), c.get(Calendar.SECOND), c.get(Calendar.DAY_OF_MONTH), c.get(Calendar.MONTH), c.get(Calendar.YEAR));

        runOnUiThread(new Runnable() {
                @Override
                public void run() {
                    timer.setText(finalTime);
                }
            });
    }

}, 1000, 1000); //Initial Delay and Period for update (in milliseconds)

Answer 3

声明一个处理程序来更新 UI 线程上的 TextView。

private Handler mHandler = new Handler() {
 @Override
 public void handleMessage(Message msg) {
    time = new Time();
    time.setToNow();

    timeString = time.toString();
    changeTime = Parser(timeString); 
    timer.setText(changeTime);  
 }
};

启动一个 TimeTask 来更新你的 TextView

int initialDelay = 1000; //first update in miliseconds
int period = 5000;      //nexts updates in miliseconds       

Timer timer = new Timer();
TimerTask task = new TimerTask() {
  public void run() {
      Message msg = new Message();
      mHandler.sendMessage(msg);
  }
};
timer.scheduleAtFixedRate(task, initialDelay, period);

Answer 4

这可以借助 android 中的线程轻松完成，但由于您想访问 ui，因此线程无法帮助您。你最好选择 handlers 或 timertask

但是异步任务也在非 ui 线程上运行，所以在 timertask 中创建一个处理程序..

Timer t=Timer();

    t.scheduleAtFixedRate(new TimerTask(new Runnable()
        {
    public void run(){
    Handler h=new Handler(getMainLooper());
    h.post(new Runnable(
){public void run(){
//get the time here and set the textview here as here it has access to the main ui
}});
    }
    }
    ), long delay, Long period);

抱歉，代码格式不正确......但它会为您工作

Answer 5

如果操作不耗时，建议使用Handler，而不是Timer或Thread。 Handler 在当前线程中工作，不会创建新线程，这样可以节省一些内存使用。它还通过减少 CPU 轮询线程的数量来节省一些 CPU 使用率。此外，Android 的线程Looper 和时钟SysClock 进行了优化，等待时几乎不消耗资源。

Handler handler = new Handler(Looper.getMainLooper()) // using the main thread to update view
Runnable runnable = new Runnable() {
    public void run(){
        tick()
    }
}
void tick(){
    Date date = Date()
    String text = date.toString() // or using SimpleDateFormat
    textView.setText(text)
    handler.postDelayed(runnable, 1000)
}

记得手动结束。

void onDestroy() {
    super.onDestroy()
    handler.removeCallbacks(runnable)
}