Question

我正在尝试创建一个应用程序，您可以使用EditText和ListView将项目添加到列表中。我正在使用this website来帮助，因为我没有太多的android编码经验，但我不得不稍微更改代码，因为我使用的是两个活动而不是一个。但是我的ListView已经消失了，我不知道为什么。

Questions.java（ListView活动）

package com.example.sylvie.dogwise;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import android.widget.ArrayAdapter;
import android.widget.ListView;

public class Questions extends AppCompatActivity {
    ListView listview;
    String[] ListElements = new String[] {
            "Question 1",
            "Question 2"
    };
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_questions);

        Bundle newQuestion = getIntent().getExtras();
        if (newQuestion==null){
            return;
        }
        String QuestionName = newQuestion.getString("QuestionName");

        listview = (ListView) findViewById(R.id.QuestionsList);

        final List<String> ListElementsArrayList = new ArrayList<String>(Arrays.asList(ListElements));
        final ArrayAdapter<String> adapter = new ArrayAdapter<String>
                (Questions.this, android.R.layout.simple_list_item_1, ListElementsArrayList);

        ListElementsArrayList.add(QuestionName);
        adapter.notifyDataSetChanged();
    }

    public void backHomeOnClick(View view){
        Intent b = new Intent(this, HomeScreen.class);
        startActivity(b);
    }

    public void askAQuestionOnClick(View view){
        Intent i = new Intent(this, AskAQuestion.class);
        startActivity(i);
    }
    }

activity_questions.xml（ListView活动）

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.sylvie.dogwise.Questions">

    <Button
        android:id="@+id/qBackButton"
        android:layout_width="88dp"
        android:layout_height="wrap_content"
        android:text="Back"
        android:onClick="backHomeOnClick"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintLeft_toLeftOf="parent" />

    <ListView
        android:id="@+id/QuestionsList"
        android:layout_width="384dp"
        android:layout_height="wrap_content"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/qBackButton" />

    <Button
        android:id="@+id/AskAQuestionButton"
        android:layout_width="384dp"
        android:layout_height="50dp"
        android:layout_marginBottom="0dp"
        android:layout_marginLeft="0dp"
        android:layout_marginRight="0dp"
        android:text="Ask a Question"
        android:onClick="askAQuestionOnClick"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent" />

</android.support.constraint.ConstraintLayout>

AskAQuestion.java（EditText活动）

package com.example.sylvie.dogwise;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;

public class AskAQuestion extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_ask_aquestion);
    }
    public void backQuestionsOnClick(View view){
        Intent b = new Intent(this, Questions.class);
        startActivity(b);
    }
    public void okOnClick(View view){
        Intent o = new Intent(this, Questions.class);

        final EditText QuestionInput = (EditText) findViewById(R.id.editText);
        String Question = QuestionInput.getText().toString();

        o.putExtra("QuestionName", Question);

        startActivity(o);
    }
}

activity_ask_aquestion.xml（EditText活动）

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.sylvie.dogwise.AskAQuestion">

    <Button
        android:id="@+id/aaqBackButton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="0dp"
        android:layout_marginTop="0dp"
        android:onClick="backQuestionsOnClick"
        android:text="Back"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <EditText
        android:id="@+id/editText"
        android:layout_width="350dp"
        android:layout_height="wrap_content"
        android:layout_marginLeft="16dp"
        android:layout_marginRight="16dp"
        android:ems="10"
        android:inputType="textPersonName"
        android:text="Question"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        android:layout_marginTop="100dp" />

    <Button
        android:id="@+id/okButton"
        android:layout_width="100dp"
        android:layout_height="50dp"
        android:layout_marginLeft="16dp"
        android:layout_marginRight="16dp"
        android:layout_marginTop="32dp"
        android:text="OK"
        android:onClick="okOnClick"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/editText" />
</android.support.constraint.ConstraintLayout>

Answer 1

您需要致电listview. setAdapter（adapter）

public class Questions extends AppCompatActivity {

    // fields
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        // code ...
        // no need of notifyDataSetChanged 
        listview.setAdapter(adapter);
       // from this moment on, use adapter.notifyDataSetChanged
       // to indicate changes in dataset 
    }
  // other methods
}

ListView没有显示？

1 个答案: