在异步任务中使用runOnUiThread()方法来隐藏进度条。

示例代码如下：

public class MainActivity extends AppCompatActivity {

    private ProgressBar mProgressBar;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mProgressBar = findViewById(R.id.progressBar);

        // 设置点击事件
        findViewById(R.id.button).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // 启动异步任务
                new MyAsyncTask().execute();
            }
        });
    }

    private class MyAsyncTask extends AsyncTask {

        @Override
        protected void onPreExecute() {
            // 显示进度条
            mProgressBar.setVisibility(View.VISIBLE);
        }

        @Override
        protected Void doInBackground(Void... voids) {
            // 模拟长时间的操作
            try {
                Thread.sleep(5000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

            return null;
        }

        @Override
        protected void onPostExecute(Void aVoid) {
            // 隐藏进度条
            runOnUiThread(new Runnable() {
                @Override
                public void run() {
                    mProgressBar.setVisibility(View.GONE);
                }
            });
        }
    }
}