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();
         }
     }
 }