问如何制作依赖于其他应用的Android应用？

EN

try{
    Intent intent = new Intent("com.google.zxing.client.android.SCAN");
    intent.setPackage("com.google.zxing.client.android");
    startActivityForResult(intent, 0);
} catch (Exception e) {
    createAlert("Barcode Scanner not installed!", "This application uses " +
    "the open source barcode scanner by ZXing Team, you need to install " +
    "this before you can use this software!", true);
}

public void createAlert(String title, String message, Boolean button) {
    // http://androidideasblog.blogspot.com/2010/02/how-to-add-messagebox-in-android.html
    AlertDialog alertDialog;
    alertDialog = new AlertDialog.Builder(this).create();
    alertDialog.setTitle(title);
    alertDialog.setMessage(message);
    if ((button == true)) {
        alertDialog.setButton("Download Now",
        new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface arg0, int arg1) {
                Intent browserIntent = new Intent(
                    Intent.ACTION_VIEW,
                    Uri.parse("market://search?q=pname:com.google.zxing.client.android"));
                startActivity(browserIntent);
            }
        });
    }
    alertDialog.show();
}