让ProgressDialog在setCancelable(false)时按返回键可dismiss

最近发现Android4.0系统中ProgressDialog设置为setCancelable(true)时，点击ProgressDialog以外的区域也可以让ProgressDialog dismiss掉。但有时我们不希望是这样的效果，于是将ProgressDialog设置setCancelable(false)，再点击ProgressDialog以外的区域就不会出现前面所说的情况了，然而这样以来再按返回键时就不起作用了，只能等待程序执行到dissmiss处为止。其实，只要为ProgressDialog添加KeyListener来对返回键予以处理就可以解决这个问题了。

package cn.winfirm.examples.base;

import android.app.Activity;
import android.app.ProgressDialog;
import android.content.DialogInterface;
import android.content.DialogInterface.OnKeyListener;
import android.os.Bundle;
import android.view.KeyEvent;
import android.view.Window;

/**
 * Activity的基类，带一个ProgressDialog，可双击取消其显示
 *
 * @author savant
 *
 */
public class BaseActivity extends Activity {

    private ProgressDialog progressDialog  = null;

    @Override
    protected  void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        requestWindowFeature(Window.FEATURE_NO_TITLE);
    }

    /**
     * show loading progress dialog
     */
    public void showDialog() {
        if (null == progressDialog) {
            progressDialog = ProgressDialog.show(BaseActivity.this, "",  "正在加载，请稍候...");
            progressDialog.setCancelable(false);
        } else {
            progressDialog.show();
        }
        progressDialog.setOnKeyListener(onKeyListener);
    }

    /**
     * add a keylistener for progress dialog
     */
    private OnKeyListener onKeyListener  = new OnKeyListener() {
        @Override
        public  boolean onKey(DialogInterface  dialog, int keyCode, KeyEvent event) {
            if  (keyCode == KeyEvent.KEYCODE_BACK &&  event.getAction() ==  KeyEvent.ACTION_DOWN) {
                dismissDialog();
            }
            return false;
        }
    };

    /**
     * dismiss dialog
     */
    public void dismissDialog() {
        if (isFinishing()) {
            return;
        }
        if (null != progressDialog && progressDialog.isShowing()) {
            progressDialog.dismiss();
        }
    }

    /**
     * cancel progress dialog if nesseary
     */
    @Override
    public void onBackPressed() {
        if (progressDialog !=  null && progressDialog.isShowing()) {
            dismissDialog();
        } else {
            super.onBackPressed();
        }
    }
}