如果你深入挖掘android代码，你会发现这些行清楚地表明，我们不能改变Toast消息的持续时间。

 NotificationManagerService.scheduleTimeoutLocked() {
    ...
    long delay = immediate ? 0 : (r.duration == Toast.LENGTH_LONG ? LONG_DELAY : SHORT_DELAY);
    }

持续时间的默认值为

private static final int LONG_DELAY = 3500; // 3.5 seconds
private static final int SHORT_DELAY = 2000; // 2 seconds

计划一个倒计时，直到将来的某个时间，并在此过程中定期通知。在文本框中显示30秒倒计时的例子:

     new CountDownTimer(30000, 1000) {

     public void onTick(long millisUntilFinished) {
         mTextField.setText("seconds remaining: " + millisUntilFinished / 1000);
     }

     public void onFinish() {
         mTextField.setText("done!");
     }
  }.start();

用户不能自定义吐司的持续时间。因为NotificationManagerService的scheduleTimeoutLocked()函数没有使用字段duration。源代码如下。

private void scheduleTimeoutLocked(ToastRecord r, boolean immediate)
    {
        Message m = Message.obtain(mHandler, MESSAGE_TIMEOUT, r);
        long delay = immediate ? 0 : (r.duration == Toast.LENGTH_LONG ? LONG_DELAY : SHORT_DELAY);
        mHandler.removeCallbacksAndMessages(r);
        mHandler.sendMessageDelayed(m, delay);
    }

这段文字将在5秒内消失。

    final Toast toast = Toast.makeText(getApplicationContext(), "My Text", Toast.LENGTH_SHORT);
    toast.show();

    Handler handler = new Handler();
        handler.postDelayed(new Runnable() {
           @Override
           public void run() {
               toast.cancel(); 
           }
    }, 5000); // Change to what you want

编辑: 正如Itai Spector在评论中所说，它将显示约3.5秒，所以使用以下代码:

    int toastDuration = 5000; // in MilliSeconds
    Toast mToast = Toast.makeText(this, "My text", Toast.LENGTH_LONG);
    CountDownTimer countDownTimer;
    countDownTimer = new CountDownTimer(toastDuration, 1000) {
        public void onTick(long millisUntilFinished) {
            mToast.show();
        }

        public void onFinish() {
            mToast.cancel();
        }
    };

    mToast.show();
    countDownTimer.start();

下面是我用上面的代码创建的一个自定义Toast类:

import android.content.Context;
import android.os.CountDownTimer;
import android.widget.Toast;

public class CustomToast extends Toast {
    int mDuration;
    boolean mShowing = false;
    public CustomToast(Context context) {
        super(context);
        mDuration = 2;
    }


    /**
     * Set the time to show the toast for (in seconds) 
     * @param seconds Seconds to display the toast
     */
    @Override
    public void setDuration(int seconds) {
        super.setDuration(LENGTH_SHORT);
        if(seconds < 2) seconds = 2; //Minimum
        mDuration = seconds;
    }

    /**
     * Show the toast for the given time 
     */
    @Override
    public void show() {
        super.show();

        if(mShowing) return;

        mShowing = true;
        final Toast thisToast = this;
        new CountDownTimer((mDuration-2)*1000, 1000)
        {
            public void onTick(long millisUntilFinished) {thisToast.show();}
            public void onFinish() {thisToast.show(); mShowing = false;}

        }.start();  
    }
}

如果你深入挖掘android代码，你会发现这些行清楚地表明，我们不能改变Toast消息的持续时间。

 NotificationManagerService.scheduleTimeoutLocked() {
    ...
    long delay = immediate ? 0 : (r.duration == Toast.LENGTH_LONG ? LONG_DELAY : SHORT_DELAY);
    }

持续时间的默认值为

private static final int LONG_DELAY = 3500; // 3.5 seconds
private static final int SHORT_DELAY = 2000; // 2 seconds