Question

public Update() {

         this.Data = this.Items;
         console.log(this.Data);
         for (let value of this.Data) {
             console.log(value);
         }
     }

控制台

[Object, Object, Object]

Object
CandidateName:"B"
ControlId:0
CreatedBy:null
CreationDateTime:null
ExamId1:2000
ExamName:" Safety"
Id:1292353

在最后一个对象之后显示长度：3

当我要遍历这个对象时，抛出错误的长度是未定义的，请帮助我。

Answer 1

对于迭代数组，应避免使用public class SimiliarPhotos extends AppCompatActivity implements IResult { RecyclerView rv; LinearLayoutManager llm; ArrayList<Plant> plants = new ArrayList<Plant>(); SimiliarPlantsAdapter adapter; VolleyService mVolleyService; IResult mResultCallback = null; final String GETREQUEST = "GETCALL"; //login url connection final String URL = "http://10.0.2.2:3000/plants"; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_similiar_photos); rv = (RecyclerView)findViewById(R.id.rv); llm = new LinearLayoutManager(this); llm.setAutoMeasureEnabled(true); rv.setLayoutManager(llm); initializeAdapter(); initVolleyCallback(); mVolleyService = new VolleyService(mResultCallback,this); mVolleyService.getDataVolley(GETREQUEST,URL); } @Override public void notifySuccess(String requestType, JSONObject response) { Log.d("resposta",response.toString()); } @Override public void notifySuccess(String requestType, JSONArray response) { Log.d("resposta",response.toString()); } @Override public void notifyError(String requestType, VolleyError error) { Log.d("resposta",error.toString()); } void initVolleyCallback(){ mResultCallback = new IResult() { @Override public void notifySuccess(String requestType, JSONObject response) { } @Override public void notifySuccess(String requestType, JSONArray response) { Plant plant; Log.d("ENTERED","ENTEREDHERE1"); // iterate over the JSONArray response for (int i=0; i < response.length(); i++) { try { JSONObject object = response.getJSONObject(i); // get the individual object from JSONArray int id = Integer.parseInt(object.getString("id")); // get the unique identifier from the object String specie = object.getString("specie"); // get the name of the specie from the object String description = object.getString("description"); // get the description of the object ImageLoad(specie); plant = new Plant(id,specie,description); // construct the object Log.d("plant",String.valueOf(plant)); plants.add(plant); // add the object to the arraylist so it can be used on the cardLayout } catch (JSONException e) { Log.d("ENTERED",e.toString()); e.printStackTrace(); } } adapter.notifyDataSetChanged(); } @Override public void notifyError(String requestType, VolleyError error) { Log.d("resposta",error.toString()); } }; } public void ImageLoad(String specie){ String urlFoto = "http://10.0.2.2:3000/images/" + specie + "/Thumbnail.jpg"; Picasso.with(this) .load(urlFoto) .into(imageView); } public void initializeAdapter(){ Log.d("plants",String.valueOf(plants.size())); adapter = new SimiliarPlantsAdapter(plants); rv.setAdapter(adapter); } }或for in语句。它有两个“缺点”：

1）订单不保证

2）如果可枚举，则列出/枚举继承的属性：定义属性时未指定false。

例如，如果您向原型添加属性，则此循环也将迭代该原型。

for of

您还应该看到您的财产已打印出来。

如果将循环更改为顺序for循环：

Array.prototype.test = "test";
var a = ['a', 'b'];
for (let i in a) {
  console.log(a[i]);
}
for (let i of a) {
  console.log(i);
}

或a：

for (let i = 0; i < this.Data.length; i++ value of this.Data) {
  console.log(this.Data[i]);
}

您可能看不到自己的问题。

Answer 2

如果我理解正确，this.Items在某些情况下可能未定义，您无法迭代。

所以：

for (let value of (this.Data || [])) {

这可以防止不良价值

Answer 3

如果要迭代对象，则必须使用Object.keys(your_obj)。因为对象没有长度属性。您可以使用'Array'仅迭代'String'或for of类型。您可以使用Object.keys(your_obj).length进行顺序循环for(var i=0; i<Object.keys(your_obj).length; i++)

public Update() {

         this.Data = this.Items;
         console.log(this.Data);
         for (let obj of this.Data) {
             console.log(obj);
             //iterate over object here
             for(let property of Object.keys(obj)){
               // write your logic for specific object
             }
         }
     }

扩展到quirimmo的答案，顺序循环，使用此

     this.Data.forEach(function(obj){
         console.log(obj);
         //iterate over object here
         for(var i=0; i<Object.keys(obj).length; i++){
           // write your logic for specific object
         }
     })

Typescript：Typescript循环显示未定义

3 个答案: