任何人都可以帮助我理解 Android Studio 中的 SharedPreferences

Question

I am building a pokedex app in which the app needs to remember the saved pokemons but the documentation for SharedPreferences is very confusing. How do i add that in PokemonActivity. I know that it needs to be added along with button for "Catch/Release" but how do i do that. Is it like a variable for like a function is what i am really confused about.

 PokemonActivity.java import androidx.appcompat.app.AppCompatActivity; import android.graphics.Bitmap; import android.graphics.BitmapFactory; import android.os.AsyncTask; import android.os.Bundle; import android.util.Log; import android.view.View; import android.widget.Button; import android.widget.ImageView; import android.widget.TextView; import com.android.volley.Request; import com.android.volley.RequestQueue; import com.android.volley.Response; import com.android.volley.VolleyError; import com.android.volley.toolbox.JsonObjectRequest; import com.android.volley.toolbox.Volley; import org.json.JSONArray; import org.json.JSONException; import org.json.JSONObject; import java.io.IOException; import java.net.URL; public class PokemonActivity extends AppCompatActivity { private TextView nameTextView; private TextView numberTextView; private TextView type1TextView; private TextView type2TextView; private String url; private RequestQueue requestQueue; private Button button; ImageView imageView; private TextView pokemondesc; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_pokemon); requestQueue = Volley.newRequestQueue(getApplicationContext()); url = getIntent().getStringExtra("url"); nameTextView = findViewById(R.id.pokemon_name); numberTextView = findViewById(R.id.pokemon_number); type1TextView = findViewById(R.id.pokemon_type1); type2TextView = findViewById(R.id.pokemon_type2); button = findViewById(R.id.catchbutton); imageView = findViewById(R.id.pokemon_image); pokemondesc = findViewById(R.id.pokemon_desc); load(); } public void load() { type1TextView.setText(""); type2TextView.setText(""); JsonObjectRequest request = new JsonObjectRequest(Request.Method.GET, url, null, new Response.Listener<JSONObject>() { @Override public void onResponse(JSONObject response) { try { pokemonid = response.getInt("id"); String url1 = "https://pokeapi.co/api/v2/pokemon-species/" + pokemonid + "/"; final JsonObjectRequest requestdisc = new JsonObjectRequest(Request.Method.GET, url1, null, new Response.Listener<JSONObject>() { @Override public void onResponse(JSONObject response) { try { JSONArray flavorEntries = response.getJSONArray("flavor_text_entries"); for (int i = 0; i < flavorEntries.length(); i++) { JSONObject description = flavorEntries.getJSONObject(i); String lang = description.getJSONObject("language").getString("name"); if(lang.equals("en")){ String flavorText = description.getString("flavor_text"); pokemondesc.setText(flavorText); break; } } } catch (JSONException e) { Log.e("cs50", "Json error", e); } } }, new Response.ErrorListener() { @Override public void onErrorResponse(VolleyError error) { Log.e("cs50", "flavorText list error", error); } }); requestQueue.add(requestdisc); nameTextView.setText(response.getString("name")); numberTextView.setText(String.format("#%03d", response.getInt("id"))); String imgUrl = response.getJSONObject("sprites").getString("front_default"); new DownloadSpriteTask().execute(imgUrl); JSONArray typeEntries = response.getJSONArray("types"); for (int i = 0; i < typeEntries.length(); i++) { JSONObject typeEntry = typeEntries.getJSONObject(i); int slot = typeEntry.getInt("slot"); String type = typeEntry.getJSONObject("type").getString("name"); if (slot == 1) { type1TextView.setText(type); } else if (slot == 2) { type2TextView.setText(type); } } } catch (JSONException e) { Log.e("cs50", "Pokemon json error", e); } } }, new Response.ErrorListener() { @Override public void onErrorResponse(VolleyError error) { Log.e("cs50", "Pokemon details error", error); } }); requestQueue.add(request); } public boolean pokemonIsCaught = false; public void toggleCatch(View view) { // gotta catch 'em all! if (!pokemonIsCaught) { pokemonIsCaught = true; button.setText("Release"); } else { pokemonIsCaught = false; button.setText("Catch"); } } private class DownloadSpriteTask extends AsyncTask<String, Void, Bitmap> { @Override protected Bitmap doInBackground(String... strings) { try { URL url = new URL(strings[0]); return BitmapFactory.decodeStream(url.openStream()); } catch (IOException e) { Log.e("cs50", "Download sprite error", e); return null; } } @Override protected void onPostExecute(Bitmap bitmap) { // load the bitmap into the ImageView! imageView.setImageBitmap(bitmap); } } public static int pokemonid = 0; }

EDIT 1: I Changed my code to add that SharedPreferences part like this but it does not seem to work, can anyone please help me point out the issue here.

 package edu.harvard.cs50.pokedex; import androidx.appcompat.app.AppCompatActivity; import android.content.Context; import android.content.SharedPreferences; import android.graphics.Bitmap; import android.graphics.BitmapFactory; import android.os.AsyncTask; import android.os.Bundle; import android.util.Log; import android.view.View; import android.widget.Button; import android.widget.ImageView; import android.widget.TextView; import com.android.volley.Request; import com.android.volley.RequestQueue; import com.android.volley.Response; import com.android.volley.VolleyError; import com.android.volley.toolbox.JsonObjectRequest; import com.android.volley.toolbox.Volley; import org.json.JSONArray; import org.json.JSONException; import org.json.JSONObject; import java.io.IOException; import java.net.URL; public class PokemonActivity extends AppCompatActivity { private TextView nameTextView; private TextView numberTextView; private TextView type1TextView; private TextView type2TextView; private String url; private RequestQueue requestQueue; private Button button; ImageView imageView; private TextView pokemondesc; SharedPreferences sharedpreferences; public static final String savedpok = ""; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_pokemon); requestQueue = Volley.newRequestQueue(getApplicationContext()); url = getIntent().getStringExtra("url"); nameTextView = findViewById(R.id.pokemon_name); numberTextView = findViewById(R.id.pokemon_number); type1TextView = findViewById(R.id.pokemon_type1); type2TextView = findViewById(R.id.pokemon_type2); button = findViewById(R.id.catchbutton); imageView = findViewById(R.id.pokemon_image); pokemondesc = findViewById(R.id.pokemon_desc); sharedpreferences = getSharedPreferences(savedpok, Context.MODE_PRIVATE); load(); } public void load() { type1TextView.setText(""); type2TextView.setText(""); JsonObjectRequest request = new JsonObjectRequest(Request.Method.GET, url, null, new Response.Listener<JSONObject>() { @Override public void onResponse(JSONObject response) { try { pokemonid = response.getInt("id"); String url1 = "https://pokeapi.co/api/v2/pokemon-species/" + pokemonid + "/"; final JsonObjectRequest requestdisc = new JsonObjectRequest(Request.Method.GET, url1, null, new Response.Listener<JSONObject>() { @Override public void onResponse(JSONObject response) { try { JSONArray flavorEntries = response.getJSONArray("flavor_text_entries"); for (int i = 0; i < flavorEntries.length(); i++) { JSONObject description = flavorEntries.getJSONObject(i); String lang = description.getJSONObject("language").getString("name"); if(lang.equals("en")){ String flavorText = description.getString("flavor_text"); pokemondesc.setText(flavorText); break; } } } catch (JSONException e) { Log.e("cs50", "Json error", e); } } }, new Response.ErrorListener() { @Override public void onErrorResponse(VolleyError error) { Log.e("cs50", "flavorText list error", error); } }); requestQueue.add(requestdisc); nameTextView.setText(response.getString("name")); numberTextView.setText(String.format("#%03d", response.getInt("id"))); String imgUrl = response.getJSONObject("sprites").getString("front_default"); new DownloadSpriteTask().execute(imgUrl); JSONArray typeEntries = response.getJSONArray("types"); for (int i = 0; i < typeEntries.length(); i++) { JSONObject typeEntry = typeEntries.getJSONObject(i); int slot = typeEntry.getInt("slot"); String type = typeEntry.getJSONObject("type").getString("name"); if (slot == 1) { type1TextView.setText(type); } else if (slot == 2) { type2TextView.setText(type); } } } catch (JSONException e) { Log.e("cs50", "Pokemon json error", e); } } }, new Response.ErrorListener() { @Override public void onErrorResponse(VolleyError error) { Log.e("cs50", "Pokemon details error", error); } }); requestQueue.add(request); } public boolean pokemonCaught = false; public void toggleCatch(View view) { SharedPreferences.Editor editor = sharedpreferences.edit(); String name = nameTextView.getText().toString(); // gotta catch 'em all! if (!pokemonCaught) { editor.putString(name, name); editor.apply(); editor.commit(); pokemonCaught = true; button.setText("Release"); } else { editor.remove(name); editor.apply(); editor.commit(); pokemonCaught = false; button.setText("Catch"); } } private class DownloadSpriteTask extends AsyncTask<String, Void, Bitmap> { @Override protected Bitmap doInBackground(String... strings) { try { URL url = new URL(strings[0]); return BitmapFactory.decodeStream(url.openStream()); } catch (IOException e) { Log.e("cs50", "Download sprite error", e); return null; } } @Override protected void onPostExecute(Bitmap bitmap) { // load the bitmap into the ImageView! imageView.setImageBitmap(bitmap); } } public static int pokemonid = 0; }

Answer 1

If you are confusing in shared preference you can include my gist in your project and call your desired function its help you

Click here and get Shared Preference File In Java

In your case

Save value

AppPreference.saveData(this, true, "KEY")

Get value

AppPreference.getSavedData(this, "KEY")

Answer 2

Here's a sample code that can help you get started with SharedPreferences. You can make it your base structure to develop on it further.

private SharedPreferences mPref;
private static final String SETTINGS_NAME = "default_settings";


//Initiate the shared pref
// Here, SETTINGS_NAME is a name for your shared pref
mPref = context.getSharedPreferences(SETTINGS_NAME, Context.MODE_PRIVATE);

Once you have initiated your shared pref, you can get the data like this:

//Here FieldName is a name for your data, in this case can be pokemon name
//If there is no data with the FieldName, the default value will be returned.
mPref.getString("FieldName", "DefaultValue");
mPref.getBoolean("AnotherFieldName", false);

To set a data, use this code:

//We use the Editor class of shared pref to add data
private SharedPreferences.Editor mEditor;
mEditor = mPref.edit();
mEditor.putString("FieldName", YOUR_VALUE);
mEditor.putBoolean("AnotherFieldName", BOOLEAN_VALUE);
mEditor.commit();

Read more at : Android Shared Preferences

Answer 3

Well in your case, change the code in toogleCatch method to be like this:

public void toggleCatch(View view) {

    SharedPreferences pokemonPrefs = getSharedPreferences("pokemon", 0);
    SharedPreferences.Editor editor = pokemonPrefs.edit();

    String name = nameTextView.getText().toString();

    // gotta catch 'em all!
    if (!pokemonCaught) {
        editor.putString("pokemon_name", name);
        pokemonCaught = true;
        button.setText("Release");
    } else {
        editor.putString("pokemon_name", "empty");
        pokemonCaught = false;
        button.setText("Catch");
    }
    editor.apply();

}

Then call this when you want to get the pokemon name:

SharedPreferences pokemonPrefs = this.getSharedPreferences("pokemon", 0);

String pokemonName = pokemonPrefs.getString("pokemon_name", "empty");

Change the hardcoded strings to constant later after you understand it.