Intent scanIntent = new Intent("com.google.zxing.client.android.SCAN");
Intent marketIntent = new Intent(ACTION_VIEW,Uri.parse("market://details?id=com.google.zxing.client.android"));

try {
    startActivityForResult(scanIntent);
} catch (ActivityNotFoundException e) {
    try {
        // show a prompt here
        startActivity(marketIntent);
    } catch (ActivityNotFoundException e) {
        Toast.makeText(this,"Market not installed.",LENGTH_SHORT).show();
    }

}

那么你：

>尝试启动扫描仪;>如果失败,提示用户从Android Market安装它;>如果失败,则市场未安装.