工具类

	@Override
	public boolean onKeyDown(int keyCode, KeyEvent event) {

		if (keyCode == KeyEvent.KEYCODE_BACK) {
			AlertDialog.Builder dialog = new AlertDialog.Builder(WXEntryActivity.this);
			dialog.setTitle("退出");
			dialog.setMessage("点击确定退出应用");
			dialog.setPositiveButton("确定",
					new DialogInterface.OnClickListener() {
						@Override
						public void onClick(DialogInterface dialog, int which) {
							System.exit(0);
						}
					});
			dialog.setNegativeButton("取消", null).show();
		}
		return false;
	}