如何将自定义对象的数组列表从一个 java 类传递到另一个 java 类? [英] How do I pass arraylist of a custom object from one java class to another?

问题描述

我有一个自定义对象的 Arraylist.我试图将它从一个 java 文件传递​​到另一个.我尝试了 putExtra 方法和 Parcelable 选项；但我无法理解 Parcelable.

I have an Arraylist of custom objects. I am trying to pass it from one java file to another. I tried the putExtra method and the Parcelable option; but I'm unable to understand Parcelable.

这是我的自定义对象:

public class AddValues implements Serializable{
    public int id;
    String value;

    public AddValues(int id, String value)
    {
        this.id = id;
        this.value = value;
    }

    @Override
    public String toString() {
        String result = "id = "+id+","+" value = "+value;
        return result;
    }

    public  int getid()
    {
        return  this.id;
    }

    public String getvalue()
    {
        return this.value;
    }
}

这是我发送ArrayList的代码:

Intent intent = new Intent(BluetoothLeService.this,HomePageFragment.class);
intent.putExtra("id", data_id);
intent.putExtra("value", list);

这里的list"指的是ArrayList.

Here "list" refers to the ArrayList.

推荐答案

Serializable 和 Parcelable 不是一回事，尽管它们服务于相同的目的.此帖子包含 Parcelable 对象的示例.

Serializable and Parcelable are not the same thing, although they serve the same purpose. This post contains an example of the Parcelable object.

您要创建的所有 Parcelable 对象都应遵循所采用的模式，仅更改 writeToParcel 和 AddValues(Parcel in) 方法.这两个方法应该互相映射，如果writeToParcel写一个int然后一个string，构造函数应该读一个int然后是一个 string

The pattern employed should be followed for all Parcelable objects you want to create, changing only the writeToParcel and AddValues(Parcel in) methods. These two methods should mirror eachother, if writeToParcel writes an int then a string, the constructor should read an int then a string

可包裹

public class AddValues implements Parcelable{
    private int id;
    private String value;

    // Constructor
    public AddValues (int id, String value){
        this.id = id;
        this.value= value;
   }

   // Parcelling part
   public AddValues (Parcel in){
       this.id = in.readInt();
       this.value= in.readString();
   }

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

   @Override
   public void writeToParcel(Parcel dest, int flags) {
       dest.writeInt(id);
       dest.writeString(value);
   }

   public final Parcelable.Creator CREATOR = new Parcelable.Creator() {
       public AddValues createFromParcel(Parcel in) {
           return new AddValues(in); 
       }

       public AddValues[] newArray(int size) {
           return new AddValues[size];
       }
   };

}

现在将列表添加到 Intent extra 应该很简单

Adding the list to an Intent extra should be simple now

额外添加列表

ArrayList<AddValue> list = new ArrayList<>();
Intent intent = new Intent(BluetoothLeService.this,HomePageFragment.class);
intent.putExtra("arg_key", list);

获取额外列表

ArrayList<AddValues> list = (ArrayList<AddValues>) intent.getSerializableExtra("arg_key");

顺便说一句，您可以使用 Pair 对象而不是创建 AddValues 对象.这不会影响答案，但可能很高兴知道.

As an aside, you can use the Pair<Integer, String> object instead of creating an AddValues object. This doesn't affect the answer, but might be nice to know.

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