Show link to Market if no openpgp provider installed installed

Issue #295

OpenPGP-Keychain-API/libraries/keychain-api-library/res/values/strings.xml

@@ -2,5 +2,6 @@
 <resources>
 
     <string name="openpgp_list_preference_none">None</string>
+    <string name="install_via">Install OpenKeychain via %s</string>
 
 </resources>

OpenPGP-Keychain-API/libraries/keychain-api-library/src/org/openintents/openpgp/util/OpenPgpListPreference.java

@@ -23,6 +23,7 @@ import android.content.Intent;
 import android.content.pm.ResolveInfo;
 import android.content.res.TypedArray;
 import android.graphics.drawable.Drawable;
+import android.net.Uri;
 import android.preference.DialogPreference;
 import android.util.AttributeSet;
 import android.view.View;
@@ -30,17 +31,21 @@ import android.view.ViewGroup;
 import android.widget.ArrayAdapter;
 import android.widget.ListAdapter;
 import android.widget.TextView;
+import org.sufficientlysecure.keychain.api.R;
 
 import java.util.ArrayList;
 import java.util.List;
 
-import org.sufficientlysecure.keychain.api.R;
-
 /**
  * Does not extend ListPreference, but is very similar to it!
  * http://grepcode.com/file_/repository.grepcode.com/java/ext/com.google.android/android/4.4_r1/android/preference/ListPreference.java/?v=source
  */
 public class OpenPgpListPreference extends DialogPreference {
+    private static final String OPENKEYCHAIN_PACKAGE = "org.sufficientlysecure.keychain";
+    private static final String MARKET_INTENT_URI_BASE = "market://details?id=%s";
+    private static final Intent MARKET_INTENT = new Intent(Intent.ACTION_VIEW, Uri.parse(
+            String.format(MARKET_INTENT_URI_BASE, OPENKEYCHAIN_PACKAGE)));
+
     private ArrayList<OpenPgpProviderEntry> mProviderList = new ArrayList<OpenPgpProviderEntry>();
     private String mSelectedPackage;
 
@@ -84,6 +89,26 @@ public class OpenPgpListPreference extends DialogPreference {
             }
         }
 
+
+        // add install links if empty
+        if (mProviderList.isEmpty()) {
+            resInfo = getContext().getPackageManager().queryIntentActivities
+                    (MARKET_INTENT, 0);
+            if (!resInfo.isEmpty()) {
+                for (ResolveInfo resolveInfo : resInfo) {
+                    Intent marketIntent = new Intent(MARKET_INTENT);
+                    intent.setPackage(resolveInfo.activityInfo.packageName);
+                    Drawable icon = resolveInfo.activityInfo.loadIcon(getContext().getPackageManager());
+                    String marketName = String.valueOf(resolveInfo.activityInfo.applicationInfo
+                            .loadLabel(getContext().getPackageManager()));
+                    String simpleName = String.format(getContext().getString(R.string
+                            .install_via), marketName);
+                    mProviderList.add(new OpenPgpProviderEntry(OPENKEYCHAIN_PACKAGE, simpleName,
+                            icon, marketIntent));
+                }
+            }
+        }
+
         // add "none"-entry
         mProviderList.add(0, new OpenPgpProviderEntry("",
                 getContext().getString(R.string.openpgp_list_preference_none),
@@ -114,7 +139,22 @@ public class OpenPgpListPreference extends DialogPreference {
 
                     @Override
                     public void onClick(DialogInterface dialog, int which) {
-                        mSelectedPackage = mProviderList.get(which).packageName;
+                        OpenPgpProviderEntry entry = mProviderList.get(which);
+
+                        if (entry.intent != null) {
+                            /*
+                             * Intents are called as activity
+                             *
+                             * Current approach is to assume the user installed the app.
+                             * If he does not, the selected package is not valid.
+                             *
+                             * However  applications should always consider this could happen,
+                             * as the user might remove the currently used OpenPGP app.
+                             */
+                            getContext().startActivity(entry.intent);
+                        }
+
+                        mSelectedPackage = entry.packageName;
 
                         /*
                          * Clicking on an item simulates the positive button click, and dismisses
@@ -190,6 +230,7 @@ public class OpenPgpListPreference extends DialogPreference {
         private String packageName;
         private String simpleName;
         private Drawable icon;
+        private Intent intent;
 
         public OpenPgpProviderEntry(String packageName, String simpleName, Drawable icon) {
             this.packageName = packageName;
@@ -197,6 +238,11 @@ public class OpenPgpListPreference extends DialogPreference {
             this.icon = icon;
         }
 
+        public OpenPgpProviderEntry(String packageName, String simpleName, Drawable icon, Intent intent) {
+            this(packageName, simpleName, icon);
+            this.intent = intent;
+        }
+
         @Override
         public String toString() {
             return simpleName;