谁能告诉我为什么ListView没有显示？

Question

以下项目是从一个在线课程中逐字复制的。它应该显示一个ListView，但什么也不显示。我是一个全新的Android工作室，这只是我在里面的第二个项目。这里有5个文件，我将在下面显示每个文件的内容。我只需要另一双或两双眼睛来发现问题，因为我是“虫子盲”。任何帮助都将不胜感激。

activity_main.xml

<ListView
    android:id="@+id/listView"
    android:layout_width="0dp"
    android:layout_height="0dp"
    android:layout_marginStart="16dp"
    android:layout_marginTop="16dp"
    android:layout_marginEnd="16dp"
    android:layout_marginBottom="16dp"
    android:visibility="visible"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent" /> </androidx.constraintlayout.widget.ConstraintLayout>

MainActivity.java

package com.example.tadhg.uiuxadapterpractical;

import androidx.appcompat.app.AppCompatActivity;

import android.content.Context;
import android.content.res.TypedArray;
import android.os.Bundle;
import android.widget.ListView;

public class MainActivity extends AppCompatActivity {

  ListView lv;
  Context context;

  TypedArray images;
  String [] titleList;
  String [] descList;

  @Override
  protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);

      context = this;

      titleList = getResources().getStringArray(R.array.Languages);
      descList = 
 getResources().getStringArray(R.array.LanguageDesc);
      images = 
 getResources().obtainTypedArray(R.array.LanguageImg);

      lv = (ListView) findViewById(R.id.listView);

    }
}

OurAdapter.java

包com.example.tadhg.uiuxAdapterPractical；

导入Android.Content.Context；导入Android.content.res.TypedarRay；导入Android.View.LayoutInflater；导入Android.view.view；导入Android.View.ViewGroup；导入Android.Widget.BaseAdapter；导入Android.Widget.ImageView；导入Android.Widget.TextView；

公共类OurAdapter扩展了BaseAdapter{

private String [] titles;
private String [] desc;
private TypedArray imageID;

private Context context;
private static LayoutInflater layoutInflater;

//constructor
OurAdapter(Context adapterContext, String[] titleList, String[] descList, TypedArray images){
    titles = titleList;
    desc = descList;
    imageID = images;
    context = adapterContext;

    layoutInflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
}

@Override
public int getCount() {
    return titles.length;
}

@Override
public Object getItem(int i) {
    return i;
}

@Override
public long getItemId(int i) {
    return i;
}

private class ViewHolder {
    TextView tv1, tv2;
    ImageView img;
}

@Override
public View getView(int position, View view, ViewGroup viewGroup) {
    ViewHolder viewHolder = new ViewHolder();

    if (view == null) {
        view = layoutInflater.inflate(R.layout.list_layout, viewGroup, false);
        viewHolder.tv1 = (TextView)view.findViewById(R.id.textView7);
        viewHolder.tv2 = (TextView)view.findViewById(R.id.textView8);
        viewHolder.img = (ImageView) view.findViewById(R.id.imageView2);

        view.setTag(viewHolder);
    } else {
        viewHolder = (ViewHolder) view.getTag();
    }

    viewHolder.tv1.setText(titles[position]);
    viewHolder.tv2.setText(desc[position]);
    viewHolder.img.setImageResource(imageID.getResourceId(position, 0));

    return view;
} }

list_layout.xml

html" target="_blank">xmlns:tools=“http://schemas.android.com/tools”android:layout_width=“match_parent”android:layout_height=“match_parent”">

<ImageView
    android:id="@+id/imageView2"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginStart="16dp"
    android:layout_marginTop="8dp"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    app:srcCompat="@drawable/cplus" />

<TextView
    android:id="@+id/textView7"
    android:layout_width="0dp"
    android:layout_height="32dp"
    android:layout_marginStart="16dp"
    android:layout_marginTop="8dp"
    android:layout_marginEnd="8dp"
    android:text="TextView"
    android:textSize="24sp"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toEndOf="@+id/imageView2"
    app:layout_constraintTop_toTopOf="parent" />

<TextView
    android:id="@+id/textView8"
    android:layout_width="0dp"
    android:layout_height="24dp"
    android:layout_marginStart="16dp"
    android:layout_marginTop="8dp"
    android:layout_marginEnd="8dp"
    android:text="TextView"
    android:textSize="18sp"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toEndOf="@+id/imageView2"
    app:layout_constraintTop_toBottomOf="@+id/textView7"
    tools:text="TextView" />

Strings.xml

<string-array name="Languages">
    <item>Java</item>
    <item>Swift</item>
    <item>C#</item>
    <item>SQL</item>
    <item>Javascript</item>
    <item>Jquery</item>
    <item>C++</item>
</string-array>

<string-array name="LanguageDesc">
    <item>Desc. of Java</item>
    <item>Desc. of Swift</item>
    <item>Desc. of C#</item>
    <item>Desc. of SQL</item>
    <item>Desc. of Javascript</item>
    <item>Desc. of Jquery</item>
    <item>Desc. of C++</item>
</string-array>

<array name="LanguageImg">
    <item>@drawable/java</item>
    <item>@drawable/swift</item>
    <item>@drawable/csharp</item>
    <item>@drawable/sql</item>
    <item>@drawable/js</item>
    <item>@drawable/jquery</item>
    <item>@drawable/cplus</item>
</array> </resources>

Answer 1

您没有将适配器附加到listview...您必须将适配器设置为listview，然后只有您才会看到listview

使用以下代码更改代码

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    context = this;

    titleList = getResources().getStringArray(R.array.Languages);
    descList =
            getResources().getStringArray(R.array.LanguageDesc);
    images =
            getResources().obtainTypedArray(R.array.LanguageImg);
    final OurAdapter adapter = new OurAdapter(getApplicationContext(),titleList,descList,images);
    lv = (ListView) findViewById(R.id.listView);
    lv.setAdapter(adapter);

}

Answer 2

在listview中,您有：

android:layout_width="0dp"
android:layout_height="0dp"

取而代之的是放

android:layout_width="match_parent"
android:layout_height="match_parent"

你强迫大小为0，这样你就看不到它了。告诉我它是否有效