button.setFocusable(true); 
button.setFocusableInTouchMode(true); 
button.requestFocus(); 
button.requestFocusFromTouch();

//带取消按钮的ProgressDialog
downloadDialog = new ProgressDialog(context);
downloadDialog.setCancelable(false);//back键不起作用,若为true,按back键，则ProgressDialog消失掉
downloadDialog.setMessage("正在下载安装包...");
downloadDialog.setButton("取消", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int i) {
  dialog.cancel();
  downApkCancel = true;
 }
});