L10: Created AnswersActivity, made models Parcelable, handling RV cli…

…ck events
AOrobator · Mar 4, 2019 · d88beec · d88beec
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diff --git a/lesson10/Lesson10_RecyclerView.md b/lesson10/Lesson10_RecyclerView.md
@@ -19,6 +19,8 @@ dependencies {
 }
 ```
 
+## RecyclerView Layout
+
 Now we'll work on our layouts. We'll start off with `list_item_question.xml`, which will be the 
 layout for each individual list item. You'll want to use a combination of `MaterialCardView`, 
 `ConstraintLayout`, and a `ChipGroup` inside a `HorizontalScrollView`. Don't worry about making the 
@@ -63,6 +65,8 @@ is the most common LayoutManager you'll use, but there is also, `StaggeredGridLa
 item for our layout preview. Note that since this is in the tools namespace, it doesn't affect our 
 final app at all.
 
+## Loading RecyclerView Data
+
 `QuestionsViewModel` will take in a `QuestionsRepository` defined in `stackoverflow-api` as well as 
 an instance of `AppSchedulers` so that we can make our network call on a background thread. These 
 should be passed into the constructor and we'll use a combination of `ViewModelProvider.Factory` and
@@ -76,6 +80,8 @@ each question to our layout. Once we have this list, we'll call `setValue` on an
 `LiveData<List<QuestionViewModel>>`, our `QuestionsActivity` will observe it and pass on the result
 to the RecyclerView's adapter.
 
+## Using Adapters
+
 A `RecyclerView` gets its views from a `RecylerView.Adapter`. The adapter lets the `RecyclerView` 
 know how many views it has and how each list item should be rendered. It's also responsible for 
 notifying the `RecyclerView` when the underlying data has changed. `RecyclerView.Adapter` has a type
@@ -137,5 +143,103 @@ The third essential method is `onBindViewHolder`. Once a ViewHolder is created,
 it with the relevant information. This method allows us to do just that by passing the position in 
 the list of the ViewHolder. 
 
+## Handling Click Events
+
+It would be rather boring if all you could do was look at the items in a RecyclerView, so let's make 
+them clickable! In this app, clicking on a question should take you to AnswersActivity where the 
+answers for that particular question are shown. To start off, we'll modify our list_item so it 
+responds to touch events. Make the following modifications to the ConstraintLayout directly inside 
+the MaterialCardView:
+
+```xml
+<androidx.constraintlayout.widget.ConstraintLayout
+          android:id="@+id/clickTarget"
+          android:background="?selectableItemBackground"
+          android:clickable="true"
+          android:focusable="true">
+```
+
+We'll give it an id of clickTarget. As an aside, whenever we are referencing an id for the first 
+time, we need to use `@+id/yourId` instead of `@id/yourId`. For subsequent references, you can use
+`@id/yourId`. We then set this view's background to `?selectableItemBackground`. This, in 
+combination with setting the view as clickable and focusable, will show a touch ripple whenever this 
+view is touched or clicked.
+
+In QuestionsViewModel, we'll save a reference to the `QuestionsResponse`, and use it in the 
+following method:
+
+```java
+public void onQuestionClicked(int position) {
+  if (questionsResponse != null) {
+    Question question = questionsResponse.getItems().get(position);
+    questionLiveData.setValue(question);
+  }
+}
+```  
+
+We'll also declare a `MutableLiveData<Question>` and expose it as a `LiveData` so 
+`QuestionsActivity` can observe which `Question` is clicked. Then we'll pass `QuestionsViewModel` to
+our Adapter so each list item/`ViewHolder` can forward click events to it. In `QuestionViewHolder` 
+add the following statement to the bind method:
+
+```java
+binding
+  .clickTarget
+  .setOnClickListener(v -> 
+      this.viewModel.onQuestionClicked(getAdapterPosition()));
+```
+
+Notice how we never store the adapter position for `QuestionViewHolder`. This is because it is 
+subject to change when `QuestionViewHolder` gets recycled. Now that we're forwarding click events to
+our ViewModel, we'll want to actually react to those changes. In `QuestionsActivity`, observe 
+`QuestionsViewModel`'s `LiveData<Question>`. When this updates, we'll get an `Intent` with the 
+`Question` for `AnswersActivity`, then fire the `Intent`:
+
+```java
+@Override public void onChanged(Question question) {
+  Intent intent = AnswersActivity.getIntent(this, question);
+  startActivity(intent);
+}
+```
+
+The implementation for getIntent is pretty simple, but there's a little something going on behind 
+the scenes. We want to add our `Question` to the `Intent` as an extra so it can be retrieved by 
+`AnswersActivity`. There are many types that `Intent#putExtra` accepts, but `Question` is currently 
+not one of them. We'll fix this by making both `Question` and `User` implement the `Parcelable` 
+interface. Implementing the `Parcelable` interface allows us to easily and quickly serialize 
+objects. This will be much faster than having our model classes implement the`Serializable` 
+interface. We don't want to write out the implementation by hand, so pressing Option + Enter, after 
+declaring that you implement the `Parcelable` interface will add the `Parcelable` implementation for
+you. This gives us a couple things.
+
+First there is a new constructor that takes in a `Parcel`. When we said `Question` was a 
+`Parcelable` that means it can be written to a `Parcel`. `Parcel`s generally contain the ability to 
+read and write primitives as well as other `Parcelable`s. We also get a method 
+`writeToParcel(Parcel, int)` which does what you think it does. Notice that the data is written and 
+read from the `Parcel` in the exact same order. This is required for proper functionality.
+
+The next method we see is `describeContents`. This method should always return 0 unless you need to 
+put a FileDescriptor object into Parcelable. Then you should/must specify CONTENTS_FILE_DESCRIPTOR 
+as the return value of describeContents()
+
+The last thing we see for the `Parcelable` implementation is a static field 
+`Creator<Question> CREATOR` that can create a Question from a parcel, as well as create an array of 
+`Question`s. We'll have to make `User` implement the `Parcelable` interface as well, and we'll 
+probably want to do that before making `Question` implement the `Parcelable` interface.
+
+Once our model classes implement the `Parcelable` interface, we can retrieve the `Question` in 
+`onCreate` like so:
+
+```java
+@Override
+protected void onCreate(Bundle savedInstanceState) {
+  super.onCreate(savedInstanceState);
+  setContentView(R.layout.activity_answers);
+
+  Question question = getIntent().getParcelableExtra(KEY_QUESTION);
+}
+```
+
+
 [StackOverflow]: StackOverflow.jpg "StackOverflow"
 [StackOverflow API]: https://api.stackexchange.com/docs
diff --git a/lesson10/src/main/AndroidManifest.xml b/lesson10/src/main/AndroidManifest.xml
@@ -6,15 +6,16 @@
   <uses-permission android:name="android.permission.INTERNET"/>
 
   <application
+      android:name=".StackOverflowApplication"
       android:allowBackup="true"
       android:icon="@mipmap/ic_launcher"
       android:label="@string/app_name"
       android:roundIcon="@mipmap/ic_launcher_round"
       android:supportsRtl="true"
-      android:name=".StackOverflowApplication"
       android:theme="@style/AppTheme"
       tools:ignore="GoogleAppIndexingWarning">
-    <activity android:name=".view.QuestionsActivity">
+    <activity android:name=".answers.AnswersActivity"/>
+    <activity android:name=".questions.view.QuestionsActivity">
       <intent-filter>
         <action android:name="android.intent.action.MAIN"/>
 

diff --git a/lesson10/src/main/java/com/orobator/helloandroid/lesson10/answers/AnswersActivity.java b/lesson10/src/main/java/com/orobator/helloandroid/lesson10/answers/AnswersActivity.java
@@ -0,0 +1,26 @@
+package com.orobator.helloandroid.lesson10.answers;
+
+import android.content.Context;
+import android.content.Intent;
+import android.os.Bundle;
+import androidx.appcompat.app.AppCompatActivity;
+import com.orobator.helloandroid.lesson10.R;
+import com.orobator.helloandroid.stackoverflow.questions.Question;
+
+public class AnswersActivity extends AppCompatActivity {
+  private static final String KEY_QUESTION = "question";
+
+  public static Intent getIntent(Context context, Question question) {
+    Intent intent = new Intent(context, AnswersActivity.class);
+    intent.putExtra(KEY_QUESTION, question);
+    return intent;
+  }
+
+  @Override
+  protected void onCreate(Bundle savedInstanceState) {
+    super.onCreate(savedInstanceState);
+    setContentView(R.layout.activity_answers);
+
+    Question question = getIntent().getParcelableExtra(KEY_QUESTION);
+  }
+}
diff --git a/...10/src/main/java/com/orobator/helloandroid/lesson10/answers/di/AnswersActivityModule.java b/...10/src/main/java/com/orobator/helloandroid/lesson10/answers/di/AnswersActivityModule.java
@@ -0,0 +1,21 @@
+package com.orobator.helloandroid.lesson10.answers.di;
+
+import com.orobator.helloandroid.stackoverflow.answers.AnswersApi;
+import com.orobator.helloandroid.stackoverflow.answers.AnswersRepository;
+import com.orobator.helloandroid.stackoverflow.answers.AnswersRepositoryImpl;
+import dagger.Module;
+import dagger.Provides;
+import retrofit2.Retrofit;
+
+@Module
+public class AnswersActivityModule {
+  @Provides
+  public AnswersApi provideAnswersApi(Retrofit retrofit) {
+    return retrofit.create(AnswersApi.class);
+  }
+
+  @Provides
+  public AnswersRepository provideAnswersRepository(AnswersApi answersApi) {
+    return new AnswersRepositoryImpl(answersApi);
+  }
+}
diff --git a/lesson10/src/main/java/com/orobator/helloandroid/lesson10/di/ActivityBindingModule.java b/lesson10/src/main/java/com/orobator/helloandroid/lesson10/di/ActivityBindingModule.java
@@ -1,11 +1,17 @@
 package com.orobator.helloandroid.lesson10.di;
 
-import com.orobator.helloandroid.lesson10.view.QuestionsActivity;
+import com.orobator.helloandroid.lesson10.answers.AnswersActivity;
+import com.orobator.helloandroid.lesson10.answers.di.AnswersActivityModule;
+import com.orobator.helloandroid.lesson10.questions.di.QuestionsActivityModule;
+import com.orobator.helloandroid.lesson10.questions.view.QuestionsActivity;
 import dagger.Module;
 import dagger.android.ContributesAndroidInjector;
 
 @Module
-public abstract class ActivityBindingModule {
+abstract class ActivityBindingModule {
   @ContributesAndroidInjector(modules = { QuestionsActivityModule.class })
-  abstract QuestionsActivity bindNumberFactActivity();
+  abstract QuestionsActivity bindQuestionsActivity();
+
+  @ContributesAndroidInjector(modules = { AnswersActivityModule.class })
+  abstract AnswersActivity bindAnswersActivity();
 }
diff --git a/.../lesson10/di/QuestionsActivityModule.java → ...questions/di/QuestionsActivityModule.java b/.../lesson10/di/QuestionsActivityModule.java → ...questions/di/QuestionsActivityModule.java
@@ -1,7 +1,7 @@
-package com.orobator.helloandroid.lesson10.di;
+package com.orobator.helloandroid.lesson10.questions.di;
 
 import com.orobator.helloandroid.common.AppSchedulers;
-import com.orobator.helloandroid.lesson10.viewmodel.QuestionsViewModelFactory;
+import com.orobator.helloandroid.lesson10.questions.viewmodel.QuestionsViewModelFactory;
 import com.orobator.helloandroid.stackoverflow.questions.QuestionsApi;
 import com.orobator.helloandroid.stackoverflow.questions.QuestionsDownloader;
 import com.orobator.helloandroid.stackoverflow.questions.QuestionsRepository;

diff --git a/...roid/lesson10/view/QuestionsActivity.java → ...n10/questions/view/QuestionsActivity.java b/...roid/lesson10/view/QuestionsActivity.java → ...n10/questions/view/QuestionsActivity.java
@@ -1,17 +1,21 @@
-package com.orobator.helloandroid.lesson10.view;
+package com.orobator.helloandroid.lesson10.questions.view;
 
+import android.content.Intent;
 import android.os.Bundle;
 import androidx.appcompat.app.AppCompatActivity;
 import androidx.databinding.DataBindingUtil;
+import androidx.lifecycle.Observer;
 import androidx.lifecycle.ViewModelProviders;
 import com.orobator.helloandroid.lesson10.R;
+import com.orobator.helloandroid.lesson10.answers.AnswersActivity;
 import com.orobator.helloandroid.lesson10.databinding.ActivityQuestionsBinding;
-import com.orobator.helloandroid.lesson10.viewmodel.QuestionsViewModel;
-import com.orobator.helloandroid.lesson10.viewmodel.QuestionsViewModelFactory;
+import com.orobator.helloandroid.lesson10.questions.viewmodel.QuestionsViewModel;
+import com.orobator.helloandroid.lesson10.questions.viewmodel.QuestionsViewModelFactory;
+import com.orobator.helloandroid.stackoverflow.questions.Question;
 import dagger.android.AndroidInjection;
 import javax.inject.Inject;
 
-public class QuestionsActivity extends AppCompatActivity {
+public class QuestionsActivity extends AppCompatActivity implements Observer<Question> {
 
   @Inject QuestionsViewModelFactory viewModelFactory;
 
@@ -29,11 +33,17 @@ protected void onCreate(Bundle savedInstanceState) {
 
     binding.setVm(viewModel);
 
-    QuestionsRecyclerAdapter adapter = new QuestionsRecyclerAdapter();
+    QuestionsRecyclerAdapter adapter = new QuestionsRecyclerAdapter(viewModel);
     binding.questionsRecyclerView.setAdapter(adapter);
 
-    viewModel.questionViewModelLiveData().observe(this, adapter::updateList);
+    viewModel.questionViewModelsLiveData().observe(this, adapter::updateList);
+    viewModel.questionLiveData().observe(this, this);
 
     viewModel.loadQuestions();
   }
+
+  @Override public void onChanged(Question question) {
+    Intent intent = AnswersActivity.getIntent(this, question);
+    startActivity(intent);
+  }
 }
diff --git a/...sson10/view/QuestionsRecyclerAdapter.java → ...stions/view/QuestionsRecyclerAdapter.java b/...sson10/view/QuestionsRecyclerAdapter.java → ...stions/view/QuestionsRecyclerAdapter.java
@@ -1,4 +1,4 @@
-package com.orobator.helloandroid.lesson10.view;
+package com.orobator.helloandroid.lesson10.questions.view;
 
 import android.view.LayoutInflater;
 import android.view.ViewGroup;
@@ -8,13 +8,19 @@
 import com.google.android.material.chip.Chip;
 import com.orobator.helloandroid.lesson10.R;
 import com.orobator.helloandroid.lesson10.databinding.ListItemQuestionBinding;
-import com.orobator.helloandroid.lesson10.view.QuestionsRecyclerAdapter.QuestionViewHolder;
-import com.orobator.helloandroid.lesson10.viewmodel.QuestionViewModel;
+import com.orobator.helloandroid.lesson10.questions.view.QuestionsRecyclerAdapter.QuestionViewHolder;
+import com.orobator.helloandroid.lesson10.questions.viewmodel.QuestionViewModel;
+import com.orobator.helloandroid.lesson10.questions.viewmodel.QuestionsViewModel;
 import java.util.Collections;
 import java.util.List;
 
 public class QuestionsRecyclerAdapter extends RecyclerView.Adapter<QuestionViewHolder> {
   private List<QuestionViewModel> questionViewModels = Collections.emptyList();
+  private QuestionsViewModel viewModel;
+
+  public QuestionsRecyclerAdapter(QuestionsViewModel viewModel) {
+    this.viewModel = viewModel;
+  }
 
   @Override public int getItemCount() {
     return questionViewModels.size();
@@ -25,7 +31,7 @@ public QuestionViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int view
     LayoutInflater inflater = LayoutInflater.from(parent.getContext());
     ListItemQuestionBinding binding =
         DataBindingUtil.inflate(inflater, R.layout.list_item_question, parent, false);
-    return new QuestionViewHolder(binding);
+    return new QuestionViewHolder(binding, viewModel);
   }
 
   @Override public void onBindViewHolder(@NonNull QuestionViewHolder holder, int position) {
@@ -39,11 +45,15 @@ public void updateList(List<QuestionViewModel> questions) {
 
   static public class QuestionViewHolder extends RecyclerView.ViewHolder {
     private final ListItemQuestionBinding binding;
+    private final QuestionsViewModel viewModel;
 
-    public QuestionViewHolder(@NonNull ListItemQuestionBinding binding) {
+    public QuestionViewHolder(
+        @NonNull ListItemQuestionBinding binding,
+        QuestionsViewModel viewModel) {
       super(binding.getRoot());
 
       this.binding = binding;
+      this.viewModel = viewModel;
     }
 
     public void bind(QuestionViewModel viewModel) {
@@ -56,6 +66,11 @@ public void bind(QuestionViewModel viewModel) {
         chip.setChipBackgroundColorResource(R.color.orange_100);
         binding.chipGroup.addView(chip);
       }
+
+      binding
+          .clickTarget
+          .setOnClickListener(v ->
+              this.viewModel.onQuestionClicked(getAdapterPosition()));
     }
   }
 }
diff --git a/...lesson10/viewmodel/QuestionViewModel.java → ...uestions/viewmodel/QuestionViewModel.java b/...lesson10/viewmodel/QuestionViewModel.java → ...uestions/viewmodel/QuestionViewModel.java
@@ -1,4 +1,4 @@
-package com.orobator.helloandroid.lesson10.viewmodel;
+package com.orobator.helloandroid.lesson10.questions.viewmodel;
 
 import com.orobator.helloandroid.stackoverflow.questions.Question;
 import java.util.List;