JSON, XML, Rest služby
Abschlussbedingungen
JSON, Retrofit, RecyclerView
Retrofit
- štandardné REST API s JSON
- keď nechceme cache, request prioritization,
- Square’s Retrofit
Retrofit allows to use the following converters:
- Gson: com.squareup.retrofit:converter-gson
- Jackson: com.squareup.retrofit:converter-jackson
- Moshi: com.squareup.retrofit:converter-moshi
- Protobuf: com.squareup.retrofit:converter-protobuf
- Wire: com.squareup.retrofit:converter-wire
- Simple XML: com.squareup.retrofit:converter-simplexml
To work with Retrofit you need basically three classes.
- Model class which is used to map the JSON data to
- Interfaces which defines the possible HTTP operations
- Retrofit.Builder class - Instance which uses the interface. Builder API which allows defining the URL end point for the HTTP operation.
(Zdroj - http://vickychijwani.me/retrofit-vs-volley/)
Príklad:
zdroj: https://www.learn2crack.com/2016/02/recyclerview-json-parsing.html
build.gradle(Module:app)
dependencies {
compile fileTree(dir: 'libs', include: ['*.jar'])
androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {
exclude group: 'com.android.support', module: 'support-annotations'
})
compile 'com.android.support:appcompat-v7:23.0.1'
compile 'com.android.support:recyclerview-v7:23.1.1'
compile 'com.android.support:cardview-v7:23.2.0'
compile 'com.squareup.retrofit2:retrofit:2.0.0-beta4'
compile 'com.squareup.retrofit2:converter-gson:2.0.0-beta4'
testCompile 'junit:junit:4.12'
}
main_activity.xml, list_item.xml, RecyclerViewAdapter.java, AndroidVerzie.java sú rovnaké ako v predchádzajúcom programe VolleyPriklad1.
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent">
<android.support.v7.widget.RecyclerView
android:id="@+id/recycler_view"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:scrollbars="vertical"
android:layout_alignParentTop="true"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true" />
</RelativeLayout>
list_item,xml
<android.support.v7.widget.CardView
xmlns:card_view="http://schemas.android.com/apk/res-auto"
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginTop="5dp"
android:layout_marginLeft="5dp"
android:layout_marginRight="5dp"
card_view:cardCornerRadius="5dp">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_margin="10dp"
android:orientation="vertical">
<TextView
android:id="@+id/nazov"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="New Text"
android:textSize="18dp"
android:textStyle="bold"
android:layout_marginTop="10dp"
android:layout_marginBottom="10dp"
/>
<TextView
android:id="@+id/verzia"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="New Text" />
<TextView
android:id="@+id/api_level"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="New Text"/>
</LinearLayout>
</android.support.v7.widget.CardView>
AndroidVerzie.java
public class AndroidVerzie {
//môžeme a nemusíme použiť anotáciu SerializedName - dôležitá v prípade, keď JSON objekt propertie nie je rovnaký ako premenná
@SerializedName("ver")
private String ver;
@SerializedName("name")
private String name;
@SerializedName("api")
private String api;
public AndroidVerzie(String ver, String name, String api) {
this.ver = ver;
this.name = name;
this.api = api;
}
public String getVer() {
return ver;
}
public String getName() {
return name;
}
public String getApi() {
return api;
}
}
RecyclerViewAdapter.java
public class RecyclerViewAdapter extends RecyclerView.Adapter<RecyclerViewAdapter.ViewHolder> {
private ArrayList<AndroidVerzie> androidArrayList;
public RecyclerViewAdapter( ArrayList<AndroidVerzie> androidArrayList) {
this.androidArrayList = androidArrayList;
}
//onCreateViewHolder() táto metóda sa volá vždy, keď sa vytvorí nová inštancia ViewHolder, naplníme riadky
@Override
public RecyclerViewAdapter.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View layoutView = LayoutInflater.from(parent.getContext()).inflate(R.layout.list_item, parent, false);
return new ViewHolder(layoutView);
}
//voláme vždy, keď sa dáta zobrazia na obrazovke
@Override
public void onBindViewHolder(RecyclerViewAdapter.ViewHolder holder, int position) {
holder.nazov.setText(androidArrayList.get(position).getName());
holder.verzia.setText(androidArrayList.get(position).getVer());
holder.api_level.setText(androidArrayList.get(position).getApi());
}
@Override
public int getItemCount() {
return androidArrayList.size();
}
public class ViewHolder extends RecyclerView.ViewHolder {
private TextView nazov;
private TextView verzia;
private TextView api_level;
public ViewHolder(View itemView) {
super(itemView);
nazov = itemView.findViewById(R.id.nazov);
verzia = itemView.findViewById(R.id.verzia);
api_level = itemView.findViewById(R.id.api_level);
}
}
}
JSONResponse.java
public class JSONResponse {
private AndroidVerzie[] android;
public AndroidVerzie[] getAndroid() {
return android;
}
}
RequestInterface.java
//interface, ktorý definuje Request endpoint
public interface RequestInterface {
/*GET request na získanie JSON dát. Endpoint je definovaný v anotácií.request URL je:
http://api.learn2crack.com/android/jsonandroid ,
kde http://api.learn2crack.com je základ a android/jsonandroid je endpoint */
//request je asynchrónny Call
@GET("android/jsonandroid")
Call<JSONResponse> getJSON();
}
MainActivity.java
public class MainActivity extends AppCompatActivity {
private RecyclerView recyclerView;
private RecyclerViewAdapter adapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
recyclerView = findViewById(R.id.recycler_view);
//musím nastaviť zobrazovanie záznamov na Lineárne
RecyclerView.LayoutManager layoutManager = new LinearLayoutManager(getApplicationContext());
recyclerView.setLayoutManager(layoutManager);
nacitajJson();
}
private void nacitajJson(){
//inicializácia knižnice Retrofit, nastavenie základnej URL adresy
Retrofit retrofit = new Retrofit.Builder()
.baseUrl("http://api.learn2crack.com")
.addConverterFactory(GsonConverterFactory.create())
.build();
//vytvorený objekt RequestInterface
RequestInterface request = retrofit.create(RequestInterface.class);
//asynchrónna požiadavka (request) je vytvorený zavolaním metódy getJSON()
Call<JSONResponse> call = request.getJSON();
//asynchrónny request sa zavolá metódou enqueue(). Request môže byť úspečný, alebo neúspešný.
call.enqueue(new Callback<JSONResponse>() {
@Override
public void onResponse(Call<JSONResponse> call, Response<JSONResponse> response) {
//JSON dáta sa získajú pomocou zavolania metódy body()
JSONResponse jsonResponse = response.body();
//convertujeme ArrayObject na ArrayList
ArrayList<AndroidVerzie> data = new ArrayList<>(Arrays.asList(jsonResponse.getAndroid()));
//RecyclerView
adapter = new RecyclerViewAdapter(data);
recyclerView.setAdapter(adapter);
}
@Override
public void onFailure(Call<JSONResponse> call, Throwable t) {
Log.d("Error",t.getMessage());
}
});
}
}