英文:
Why the symbol 'add' cannot be resolved?
问题
我想创建一个数组列表，但`add`方法不起作用。package com.zaination.listview;import androidx.appcompat.app.AppCompatActivity;import android.os.Bundle;import android.widget.ListView;import java.util.ArrayList;public class MainActivity extends AppCompatActivity {@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);}ListView VarListView = (ListView) findViewById(R.id.ListView);ArrayList<String> VarArrayList = new ArrayList<String>();VarArrayList.add("Zain");VarArrayList.add("Sarmad");VarArrayList.add("Aanish");VarArrayList.add("Haider");}
英文:
I want to make an array list, but the add method is not working.
package com.zaination.listview;import androidx.appcompat.app.AppCompatActivity;import android.os.Bundle;import android.widget.ListView;import java.util.ArrayList;public class MainActivity extends AppCompatActivity {@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);}ListView VarListView = (ListView) findViewById(R.id.ListView);ArrayList<String> VarArrayList = new ArrayList<String>();VarArrayList.add("Zain");VarArrayList.add("Sarmad");VarArrayList.add("Aanish");VarArrayList.add("Haider");}
答案1
得分: 1
如果您将该代码放入onCreate（或任何其他）方法中，它可能会正常工作。
英文:
If you would put that code into onCreate (or any other) method it would probably work.
答案2
得分: 0
需要按照以下方式进行更新。```javapackage com.zaination.listview;import androidx.appcompat.app.AppCompatActivity;import android.os.Bundle;import android.widget.ListView;import java.util.ArrayList;public class MainActivity extends AppCompatActivity {@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);ListView varListView = (ListView) findViewById(R.id.ListView);ArrayList<String> varArrayList = new ArrayList<String>();varArrayList.add("Zain");varArrayList.add("Sarmad");varArrayList.add("Aanish");varArrayList.add("Haider");}}
另外，还有一个提示，属性名 VarArrayList 不遵循 Java 命名规范，应该以小写字母 varArrayList 开头。
<details><summary>英文:</summary>it's need to be updated like this.package com.zaination.listview;import androidx.appcompat.app.AppCompatActivity;import android.os.Bundle;import android.widget.ListView;import java.util.ArrayList;public class MainActivity extends AppCompatActivity {@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);ListView VarListView = (ListView) findViewById(R.id.ListView);ArrayList<String> VarArrayList = new ArrayList<String>();VarArrayList.add("Zain");VarArrayList.add("Sarmad");VarArrayList.add("Aanish");VarArrayList.add("Haider");}}also another hint attr name `VarArrayList` not follow java naming convention, should start with small letter `varArrayList`</details># 答案3**得分**: 0你把代码写在了任何方法的外部。它必须在任何一种方法中。最简单的方法是直接写在onCreate方法中：```java@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);ListView varListView = findViewById(R.id.ListView);ArrayList<String> varArrayList = new ArrayList<String>();varArrayList.add("Zain");varArrayList.add("Sarmad");varArrayList.add("Aanish");varArrayList.add("Haider");}
PS：
还有一些小的改进（也部分被Android Studio推荐）你可以进行：
- 你可以省略掉
(ListView)的强制转换，因为它是多余的。 - 你可以在初始化时省略掉ArrayList的标识符
string。 - 你应该按照小驼峰命名法的约定（如
varArrayList）来命名你的对象：
英文:
You wrote the code outside of any method. It has to be in any kind of method.
The easiest way is to write it directly into the onCreate method:
@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);ListView VarListView = (ListView) findViewById(R.id.ListView);ArrayList<String> VarArrayList = new ArrayList<String>();VarArrayList.add("Zain");VarArrayList.add("Sarmad");VarArrayList.add("Aanish");VarArrayList.add("Haider");}
PS:
There are some small improvements (also partly recommended by Android Studio) you could do:
- you can ommit the cast
(ListView)because it's redundant - you can ommit the ArrayList identifier
stringon initialization - you should name your objects (like
VarArrayList) after the lower camel case naming convention (varArrayList):
<img src="https://i.stack.imgur.com/rRRce.png" width="250">
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