Question

我正在创建简单的列表视图。所有项目将成功列出。但吐司不工作。代码的此链接我得到了错误。 Toast.makeText(this,"hello",fd.get(position),Toast.LENGTH_LONG).show();

完整代码

     import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.Toast;
import java.util.ArrayList;

public class MainActivity extends AppCompatActivity {
    ListView list;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        list = findViewById(R.id.List);
        ArrayList<String> fd = new ArrayList<String>();
        fd.add("roda");
        fd.add("ghh");
        fd.add("asfff");
        fd.add("jll");
        ArrayAdapter<String> arrayAdapter = new ArrayAdapter<String>(this,R.layout.support_simple_spinner_dropdown_item,fd);
        list.setAdapter(arrayAdapter);
        list.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id)
            {                Toast.makeText(MainActivity.this,"hello",fd.get(position),Toast.LENGTH_LONG).show();
            }
        });
    }
}

Answer 1

Toast.makeText(this,"hello"+fd.get(position),Toast.LENGTH_LONG).show();

尝试此代码

public class MainActivity extends AppCompatActivity {
    ListView list;
    private ArrayList<String> fd;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        list = findViewById(R.id.List);
        fd = new ArrayList<String>();
        fd.add("roda");
        fd.add("ghh");
        fd.add("asfff");
        fd.add("jll");
        ArrayAdapter<String> arrayAdapter = new ArrayAdapter<String>(this,R.layout.support_simple_spinner_dropdown_item,fd);
        list.setAdapter(arrayAdapter);
        list.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id)
            {                Toast.makeText(MainActivity.this,"hello"+fd.get(position),Toast.LENGTH_LONG).show();
            }
        });
    }
}

Answer 2

在类级别声明您的ArrayList对象

var obj = {
  num1: 1024,
  num2: 1025,
  num3: 1026,
  num4: 1027
}
Object.keys(obj).forEach(e => obj[e] = "0x" + obj[e].toString(16))
console.log(JSON.stringify(obj))

在ListView list; ArrayList<String> fd;

中将其初始化

onCreate()

更改代码以显示如下吐司消息

fd = new ArrayList<String>();

Answer 3

首先，必须从fd内部访问OnItemClickListener。可以通过全局声明df或使df final来实现。

第二，您不能在OnItemClickListener内使用this，因为这需要替换行

Toast.makeText(this,"hello",fd.get(position),Toast.LENGTH_LONG).show();

与此：

Toast.makeText(MainActivity.this,"hello",fd.get(position),Toast.LENGTH_LONG).show();

并用您的活动名称替换MainActivity。

从内部类错误中访问变量fd

3 个答案: