方法一：

public class  MyDialog extends Dialog {
 private int FLAG_DISMISS = 1;
 private boolean flag = true;
 
 public MyDialog(Context context) {
     super(context);
     setTitle("自動消失對話方塊測試！");
 }

@Override
 public void show() {
     super.show();
     mThread.start();
 }

@Override
 public void dismiss() {
     super.dismiss();
     flag = false;
 }

private Thread mThread = new Thread(){
     @Override
     public void run() {
  super.run();
  while(flag){
      try {
   Thread.sleep(2000);
   Message msg = mHandler.obtainMessage();
   msg.what = FLAG_DISMISS;
   mHandler.sendMessage(msg);
      } catch (InterruptedException e) {
   e.printStackTrace();
      }
  }
     }   
 };
 
 private Handler mHandler = new Handler(){
     @Override
     public void handleMessage(Message msg) {
  super.handleMessage(msg);
  if(msg.what == FLAG_DISMISS)
      dismiss();
     }
     
 };
 
    }
 

自定義一個定時器：
public static class TimeCount extends CountDownTimer 
{
    public TimeCount(long millisInFuture, long countDownInterval) 
    {
        super(millisInFuture, countDownInterval);
    }
    @Override
    public void onFinish() {
    // TODO Auto-generated method stub
    alertDialog.dismiss();//alertDialog是你的對話方塊
    }
}
然後在你自己的程式中AlertDialog部分中新增：
TimeCount timer = new TimeCount(7000, 1000);//具體時間自定
timer.start();