如何在onCreate方法中显示Dialog？

AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setTitle("Dialog Title");
builder.setMessage("Dialog Message");
builder.setPositiveButton("OK", new DialogInterface.OnClickListener() {
    public void onClick(DialogInterface dialog, int which) {
        // 点击确定按钮后的操作
    }
});
builder.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
    public void onClick(DialogInterface dialog, int which) {
        // 点击取消按钮后的操作
    }
});

AlertDialog dialog = builder.create();

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    AlertDialog.Builder builder = new AlertDialog.Builder(this);
    builder.setTitle("Dialog Title");
    builder.setMessage("Dialog Message");
    builder.setPositiveButton("OK", new DialogInterface.OnClickListener() {
        public void onClick(DialogInterface dialog, int which) {
            // 点击确定按钮后的操作
        }
    });
    builder.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
        public void onClick(DialogInterface dialog, int which) {
            // 点击取消按钮后的操作
        }
    });

    AlertDialog dialog = builder.create();
    dialog.show();
}