アプリがインストール済みか調べるとき

public boolean isInstalled(final Context context) {
    final Intent intent = new Intent(Intent.ACTION_VIEW, Uri.parse("scheme:"));
    final List resolveInfos = context.getApplicationContext()
            .getPackageManager().queryIntentActivities(intent, PackageManager.MATCH_DEFAULT_ONLY);
    return (resolveInfos != null && !resolveInfos.isEmpty());
}