I have 3 classes: MainActivity, homePage and createPage; and a list List<Recipe> recipeList = new ArrayList<>() in MainActivity.

The user enters the homePage from the MainActivity. From homePage, the user can enter createPage and create a new recipe. This new recipe is intended to be passed back to MainActivity.

I've searched online and came across parcels. But when I tried, I get a NullPointerException.

Code for createPage where the list is passed on

ArrayList<Recipe> rList = new ArrayList<>();
Recipe r = new Recipe(...);
rList.add(r)
Intent i = new Intent();
Bundle b = new Bundle();
b.putParcelableArrayList("recipe", (ArrayList<? extends Parcelable>) rList);
i.putExtras(b);
i.setClass(createPage.this, homePage.class);
startActivity(i);

Code for homePage where the list is received.

Is there something wrong with the getIntent()? Because when moving from MainActivity to homePage, it doesn't receive a bundle. Is this causing the error?

Intent intent = getIntent();
Bundle b = this.getIntent().getExtras();
if (b != null) {
    Recipe r = b.getParcelable("recipe");
    recipeList.add(r);
}

Code for Recipe class

public class Recipe implements Parcelable {

private String name;
private String description;
private String ingredients;
private int duration;
private String steps;
private int thumbnail;

protected Recipe(Parcel in) {
    name = in.readString();
    description = in.readString();
    ingredients = in.readString();
    duration = in.readInt();
    steps = in.readString();
    thumbnail = in.readInt();
}

public static final Creator<Recipe> CREATOR = new Creator<Recipe>() {
    @Override
    public Recipe createFromParcel(Parcel in) {
        return new Recipe(in);
    }

    @Override
    public Recipe[] newArray(int size) {
        return new Recipe[size];
    }
};

public String getName() {
    return name;
}
public void setName(String name) {
    this.name = name;
}

public String getDescription() {
    return description;
}
public void setDescription(String description) {
    this.description = description;
}

public String getIngredients() {
    return ingredients;
}
public void setIngredients(String ingredients) {
    this.ingredients = ingredients;
}

public int getDuration() {
    return duration;
}
public void setDuration(int duration) {
    this.duration = duration;
}

public String getSteps() { return steps; }
public void setSteps(String steps) { this.steps = steps; }

public int getThumbnail() { return thumbnail; }

public Recipe() {}

public Recipe(String name, int duration, String ingredients, String description, String steps, int thumbnail) {
    this.name = name;
    this.description = description;
    this.ingredients = ingredients;
    this.duration = duration;
    this.steps = steps;
    this.thumbnail = thumbnail;
}

@Override
public int describeContents() {
    return 0;
}

@Override
public void writeToParcel(Parcel parcel, int i) {
    parcel.writeString(name);
    parcel.writeString(description);
    parcel.writeString(ingredients);
    parcel.writeInt(duration);
    parcel.writeString(steps);
    parcel.writeInt(thumbnail);
}

}

CodePudding user response：

you are writing into Parcelable whole array under "recipe" key

b.putParcelableArrayList("recipe", (ArrayList<? extends Parcelable>) rList);

but on onther side you are looking not for list but for single Recipe item under same key

Recipe r = b.getParcelable("recipe");

you should use getParcelableArrayList or if you have only one Recipe for passing to another Activity just use putParcelable (not list)

CodePudding user response：

Alternatively you can use serializable, that will be less complex.

For reference : https://stackoverflow.com/a/2736612/9502601

Eventhough parcellables are more faster but if you want a less complex solution then you can go for it.

For Comparison between Serializable and Parcelable. https://stackoverflow.com/a/23647471/9502601

CodePudding user response：

You can use this gson Lib for this

implementation 'com.google.code.gson:gson:2.8.9'

Send Data with Intent

Recipe r = new Recipe(...);
String recipeString = new Gson().toJson(r);
intent.putExtra("recipe",recipeString);

// For ArrayList
ArrayList<Recipe> recipeList = new ArrayList<>();
String recipeString = new Gson().toJson(recipeList);
intent.putExtra("recipeList",recipeString);

Receive Data From Intent

Recipe r = new Gson().fromJson(intent.getStringExtra("recipe"), Recipe.class);

// For Array List
Type listType = new TypeToken<ArrayList<Recipe>>(){}.getType();
ArrayList<Recipe> recipeList = new Gson().fromJson(intent.getStringExtra("recipeList"),listType);