Android app UI/flow improvements (#5241)

Summary:
Pull Request resolved: #5241

- Add default system prompt
- Set temperature to 0
- Load model directly upon click

Reviewed By: cmodi-meta, kirklandsign

Differential Revision: D62472502

fbshipit-source-id: 8ecc88ee4474afa50658e93955c49ff0f3eef745

Author: Riandy

examples/demo-apps/android/LlamaDemo/app/src/main/java/com/example/executorchllamademo/PromptFormat.java

@@ -13,6 +13,7 @@ public class PromptFormat {
   public static final String SYSTEM_PLACEHOLDER = "{{ system_prompt }}";
   public static final String USER_PLACEHOLDER = "{{ user_prompt }}";
   public static final String ASSISTANT_PLACEHOLDER = "{{ assistant_response }}";
+  public static final String DEFAULT_SYSTEM_PROMPT = "Answer the questions in a few sentences";
 
   public static String getSystemPromptTemplate(ModelType modelType) {
     switch (modelType) {

examples/demo-apps/android/LlamaDemo/app/src/main/java/com/example/executorchllamademo/SettingsActivity.java

@@ -43,7 +43,7 @@ public class SettingsActivity extends AppCompatActivity {
   public SettingsFields mSettingsFields;
 
   private DemoSharedPreferences mDemoSharedPreferences;
-  public static double TEMPERATURE_MIN_VALUE = 0.1;
+  public static double TEMPERATURE_MIN_VALUE = 0.0;
 
   @Override
   protected void onCreate(Bundle savedInstanceState) {
@@ -120,6 +120,7 @@ private void setupLoadModelButton() {
                     public void onClick(DialogInterface dialog, int whichButton) {
                       mSettingsFields.saveLoadModelAction(true);
                       mLoadModelButton.setEnabled(false);
+                      onBackPressed();
                     }
                   })
               .setNegativeButton(android.R.string.no, null)
@@ -208,8 +209,7 @@ public void afterTextChanged(Editable s) {
                   new DialogInterface.OnClickListener() {
                     public void onClick(DialogInterface dialog, int whichButton) {
                       // Clear the messageAdapter and sharedPreference
-                      mSystemPromptEditText.setText(
-                          PromptFormat.getSystemPromptTemplate(mModelType));
+                      mSystemPromptEditText.setText(PromptFormat.DEFAULT_SYSTEM_PROMPT);
                     }
                   })
               .setNegativeButton(android.R.string.no, null)