为什么 Handler::postDelayed 会导致 UI 冻结

我有这个代码。我不知道为什么 postDelayed 会使 UI 在这种情况下冻结。我希望 Runnable 在 100 毫秒延迟后运行，并在 4000 毫秒内运行。

package com.delaythread;

import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.ProgressBar;

public class MyNeedActivity extends Activity implements OnClickListener {

    private ProgressBar progressBar;
    private final Handler handler = new Handler() {
        @Override
        public void handleMessage(final Message msg) {
            super.handleMessage(msg);
            progressBar.setVisibility(ProgressBar.INVISIBLE);
        }
    };

    @Override
    public void onClick(final View v) {
        if(v.getId() == R.id.button1) {
            /* This call doesn't make ProgressBar frozen.
            final Thread t = new Thread(new MyRunnable());
            t.start();
            progressBar.setVisibility(ProgressBar.VISIBLE);
             */

            // This makes ProgressBar frozen in 4000 miliseconds.
            final boolean b = handler.postDelayed(new MyRunnable(), 100);
            if(b) {
                progressBar.setVisibility(ProgressBar.VISIBLE);
            }
        }
    }

    /** Called when the activity is first created. */
    @Override
    public void onCreate(final Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        ((Button)findViewById(R.id.button1)).setOnClickListener(this);
        progressBar = (ProgressBar)findViewById(R.id.progressBar1);
    }

    private class MyRunnable implements Runnable {
        @Override
        public void run() {
            sleep();
        }

        private void sleep() {
            try {
                Thread.sleep(4000);
                handler.sendEmptyMessage(0);
            } catch (final InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

}

Update：实际上我想要的是 AsyncTask 在延迟时间后执行，所以我按照这个答案执行Java/android如何在3秒延迟后启动AsyncTask？。他说我应该使用Handler和Runnable。

根据帖子，以下内容应该适合您的需求

private final Handler handler = new Handler() {
    @Override
    public void handleMessage(final Message msg) {
        super.handleMessage(msg);
        //start Asyntask here. progress show/hide should be done in asynctaswk itself.
    }
};

@Override
public void onClick(final View v) {
    if(v.getId() == R.id.button1) {

        final boolean b = handler.postDelayed(new MyRunnable() , 1000);

    }
}

private class MyRunnable implements Runnable {
    @Override
    public void run() {
        handler.sendmessage(0);
    }
}

}