Android点击返回键back时弹出对话框Dialog

public boolean onKeyDown(int keyCode, KeyEvent event) {
if (keyCode == KeyEvent.KEYCODE_BACK && event.getRepeatCount() == 0) {
ExitDialog(MainActivity.this).show();
return true;
}

return super.onKeyDown(keyCode, event);
}

private Dialog ExitDialog(Context context) {
AlertDialog.Builder builder = new AlertDialog.Builder(context);
builder.setIcon(R.drawable.icon);
builder.setTitle("弹出对话框");
builder.setMessage("确定要××××吗，O(∩_∩)O哈哈~");
builder.setPositiveButton("确定",
new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int whichButton) {
//××××操作代码
}
});
builder.setNegativeButton("取消",
new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int whichButton) {
}
});
return builder.create();
}