要實現多選和單選功能，可以使用AlertDialog.Builder類來創建一個對話框并設置多選和單選選項。以下是一個示例代碼：

1. 單選功能：

AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setTitle("選擇一個選項");
final String[] items = {"選項1", "選項2", "選項3"};

builder.setSingleChoiceItems(items, -1, new DialogInterface.OnClickListener() {
    @Override
    public void onClick(DialogInterface dialog, int which) {
        // 點擊選項時的操作
        Toast.makeText(DialogActivity.this, "你選擇了：" + items[which], Toast.LENGTH_SHORT).show();
        dialog.dismiss();
    }
});

builder.create().show();

2. 多選功能：

AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setTitle("選擇多個選項");
final String[] items = {"選項1", "選項2", "選項3"};
final boolean[] checkedItems = {false, false, false};

builder.setMultiChoiceItems(items, checkedItems, new DialogInterface.OnMultiChoiceClickListener() {
    @Override
    public void onClick(DialogInterface dialog, int which, boolean isChecked) {
        // 多選項點擊時的操作
        checkedItems[which] = isChecked;
    }
});

builder.setPositiveButton("確定", new DialogInterface.OnClickListener() {
    @Override
    public void onClick(DialogInterface dialog, int which) {
        // 點擊確定按鈕時的操作
        StringBuilder selectedItems = new StringBuilder();
        for (int i = 0; i < items.length; i++) {
            if (checkedItems[i]) {
                selectedItems.append(items[i]).append(" ");
            }
        }
        Toast.makeText(DialogActivity.this, "你選擇了：" + selectedItems.toString(), Toast.LENGTH_SHORT).show();
        dialog.dismiss();
    }
});

builder.create().show();

通過以上代碼示例，可以實現在DialogActivity中實現多選和單選功能。