Android:具有处理程序和runnable的ListView中的多个计时器.2个问题

Question

我正在创建一个包含带有2列的ListView的应用程序.在第一列上应显示倒计时,在第二列上显示一个附加文本,用于说明倒计时的内容.下面你看到我的代码有效......或多或少.我有一个包含多行的列表视图,计时器正在滴答作响.一个问题是:我的runnable中的set.Text()似乎覆盖了所有行.例如,对于第1行可运行也将文本设置为第2行和第3行,对第2行可运行也将文本设置为1和3,依此类推.这会导致第一列闪烁(具有正确的值和其他行的值).如何为列表视图中的特定行设置文本？

下一个问题:即使我从处理程序中删除回调,runnable也会继续运行.但是当活动处于后台或关闭时,不需要计时器滴答,我不想浪费系统资源.

我的活动:

public class TimerActivity extends ListActivity {

MyTimerAdapter myTimerAdapter = null;
ArrayList<Long> timerList = new ArrayList<Long>();
ArrayList<String> textList = new ArrayList<String>();

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.listactivity);

    myTimerAdapter = new MyTimerAdapter(this, R.layout.row, R.id.tv_timer, R.id.tv_text);
    setListAdapter(myTimerAdapter);
}

@Override
protected void onResume() {
    super.onResume();
    refreshView();
}

@Override
protected void onPause() {
    myTimerAdapter.clear();
    myTimerAdapter.notifyDataSetChanged();
    super.onPause();
}

private void refreshView() {

    myTimerAdapter.clear();
    timerList.clear();
    textList.clear();

    // some code to read database and fill 
    // array timerList with a long value (used for displaying a countdown) 
    // and textList with some additional text

    myTimerAdapter.add(timerList, textList);
    myTimerAdapter.notifyDataSetChanged();
}

}

我的适配器:

public class MyTimerAdapter extends ArrayAdapter<String> {
private Activity mContext;
private ArrayList<Long> mTimer;
private ArrayList<String> mText;
private int mViewId;
private int mViewIdFieldTimer;
private int mViewIdFieldText;
private int listSize;
private ArrayList<Handler> handlerList = new ArrayList<Handler>();
private ArrayList<TimerRunnable> runList = new ArrayList<TimerRunnable>();

public MyTimerAdapter(Activity context, int textViewResId, int tv1, int tv2) {
    super(context, textViewResId);
    mContext = context;
    mViewId = textViewResId;
    mViewIdFieldTimer = tv1;
    mViewIdFieldText = tv2;
    listSize = 0;
}

public void add(ArrayList<Long> timer, ArrayList<String> text) {
    mTimer = timer;
    mText = text;
    listSize = mText.size();
    handlerList.clear();
    runList.clear();
}

@Override
public void clear() {
    super.clear();
    int i;
    for (i=0; i<listSize; i++) {
        handlerList.get(i).removeCallbacksAndMessages(runList.get(i));
        runList.get(i).stopHandler();
    }
}

@Override
public int getCount() {
    return listSize;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    View v = convertView;
    if (v == null) {
        LayoutInflater vi = mContext.getLayoutInflater();
        v = vi.inflate(mViewId, null);
    }

    long timerLine = mTimer.get(position);
    if (timerLine != 0) {
        TextView tvTimer = (TextView) v.findViewById(mViewIdFieldTimer);

        if (tvTimer != null) {
            tvTimer.setTag(position);
            final Handler mTimerHandler = new Handler();
            TimerRunnable timerTask = new TimerRunnable(tvTimer, tvTimer.getTag().toString(), timerLine);
            mTimerHandler.post(timerTask);

            // save in array to stop later
            handlerList.add(mTimerHandler);
            runList.add(timerTask);
        }
    }

    String textLine = mText.get(position);
    if (textLine != null) {
        TextView tvText = (TextView) v.findViewById(mViewIdFieldText);
        if (tvText != null) {
            tvText.setText(textLine);
        }
    }

    return v;
}
}

我的Runnable:

public class TimerRunnable implements Runnable {
private TextView tv;
final Handler mTimerHandler = new Handler();
String tag;
long endtime;
long sec;

public TimerRunnable (TextView tv, String tag, long endtime) {
    this.tv = tv;
    this.tag = tag;
    this.endtime = endtime;
}

public void run() {
    if (tv.getTag().toString().equals(tag)) {
        Calendar cal = Calendar.getInstance();
        sec = endtime - (cal.getTimeInMillis() / 1000); //endtime - aktuelle Zeit
        if (sec >= 0) {

            // some code formatting the time in seconds to something like hh:mm:ss (var String txt)

            tv.setText(txt);

            System.out.println(txt);  // only for tests; so I could see that runnable is still running

            mTimerHandler.postDelayed(this, 1000);
        } 
    }
}

public void stopHandler() {
    mTimerHandler.removeCallbacksAndMessages(null);
}
}

Answer 1

我会这样做:

1. 使用计时器(http://developer.android.com/reference/java/util/Timer.html)让它每秒钟或其他任何时间定期运行.
2. 在Activities onCreate()中创建Timer对象,并在Activities onDestroy()中取消()更新计时器(或者更好地在onResume中启动它并在onPause()中取消它).这就是如何避免内存泄漏的最简单方法,即使活动已关闭,您的计时器也在运行.

3. 从正在运行的计时器更新ListView.有两种选择:

   • 只需adapter.notifyDatasetChanged()从您的计时器打电话.但这可能会导致"闪烁"的列表视图.但是,您可以尝试检查这是否可以在您的应用程序中工作,因为这是最简单的实现.

   • 直接更新ListView中当前可见的TextView

     private void updateTime(){
     
     int firstVisibleItemIndex = listView.getFirstVisiblePosition();
     
     for (int i = 0; i < listView.getChildCount(); i++) {
         View v = listView.getChildAt(i);
     
             YourItem item = (YourItem)adapter
                     .getItem(firstVisibleItemIndex + i));
     
             ViewHolder vh = (ViewHolder) v.getTag();
                                 // Calculate the time somehow, i.e. call a methot on your data item
                                 vh.tvTimer.setText(item.getElapsedTime());
     
     
         }
     
     }
     

     }

所以我猜第二种选择是最好的.您可能想知道ViewHolder是什么.ViewHolder是一种提高ListView性能的模式.http://developer.android.com/training/improving-layouts/smooth-scrolling.html#ViewHolder 适配器的问题是,每次用户滚动时都会调用findViewById().findViewById()是一种昂贵的方法调用,因为它必须遍历所有视图子节点以找到具有给定id的节点.在您的简单适配器中,它可能不会产生太大影响(因为您只有一个子视图,TextView).但ViewHolder是您应该在Adapter实现中始终使用的东西