尽管 ListView 和 Simple Adapter 有数据，Android ListView 不显示项目

Question

我不确定为什么结果没有出现在我的 ListView 中。我什至有调试日志告诉我适配器和列表视图都有 2 个项目，但它仍然没有显示任何内容。这是代码

SelectPlayerActivity.java

PlayerDB db = new PlayerDB(this);
ArrayList<Player> data = db.getPlayers();
ArrayList<HashMap<String, String>> hashData = new ArrayList<HashMap<String, String>>();
for (Player player : data){
    hashData.add(Player.ConvertPlayerToHashMap(player));
}

// create the resource, from, and to variables
int resource = R.layout.playerlist_row;
String[] from = {"name"};
int[] to = {R.id.playerName};

// create and set the adapter
SimpleAdapter adapter =
        new SimpleAdapter(this, hashData, resource, from, to);
listPlayers.setAdapter(adapter);
adapter.notifyDataSetChanged();

// Both of these show the right amount of data, showing up as 2
Log.d("SelectPlayerActivity", "Adapter counted: " + adapter.getCount());
Log.d("SelectPlayerActivity", "ListView counted: " + listPlayers.getCount());

listPlayers.setOnItemClickListener(new AdapterView.OnItemClickListener() {
    @Override
    public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
        HashMap<String, String> hashPlayer = (HashMap<String, String>)listPlayers.getAdapter().getItem(position);
        if (hashPlayer.getClass() != HashMap.class) {
            Log.e("SelectPlayerActivity", "Error! hashPlayer is not a HashMap!");
        }
        else {
            selectedPlayer = Player.ConvertHashMapToPlayer(hashPlayer);
            finish();
        }
    }
});

我还包含了布局文件，以防它们出现问题

activity_select_player.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.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=".SelectPlayerActivity">

    <TextView
        android:id="@+id/lblName"
        android:layout_width="79dp"
        android:layout_height="43dp"
        android:layout_marginStart="12dp"
        android:layout_marginLeft="12dp"
        android:layout_marginTop="12dp"
        android:gravity="center"
        android:text="Player"
        android:textSize="18sp"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/btnApplySelection"
        android:layout_width="381dp"
        android:layout_height="103dp"
        android:text="Apply Selection &amp; Return to Menu"
        android:textSize="18sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent" />

    <EditText
        android:id="@+id/txtName"
        android:layout_width="292dp"
        android:layout_height="45dp"
        android:layout_marginTop="12dp"
        android:ems="10"
        android:hint="Use the list below to select a player"
        android:inputType="text"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.333"
        app:layout_constraintStart_toEndOf="@+id/lblName"
        app:layout_constraintTop_toTopOf="parent" />

    <ListView
        android:id="@+id/listPlayers"
        android:layout_width="409dp"
        android:layout_height="568dp"
        android:layout_marginBottom="1dp"
        app:layout_constraintBottom_toTopOf="@+id/btnApplySelection"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="1.0" />
</androidx.constraintlayout.widget.ConstraintLayout>

playerlist_row.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content">

    <TextView
        android:id="@+id/playerName"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="20sp"/>

</LinearLayout>

EDIT1我已经包含了来自下面的 hashMap 变量的数据，与从日志中复制的完全一样

hashData = {ArrayList@11212}  size = 2
 0 = {HashMap@11269}  size = 5
  "wins" -> "0"
  "ties" -> "0"
  "name" -> "Marky"
  "id" -> "1"
  "losses" -> "0"
 1 = {HashMap@11270}  size = 5
  "wins" -> "0"
  "ties" -> "0"
  "name" -> "asdasd"
  "id" -> "2"
  "losses" -> "0"

Answer 1

ListView 在那里，但是因为你让它有一个固定的高度568dp 它的两行呈现在其他Views 的“后面”，例如应用栏（在我的示例应用中是第二行部分可见，并且第一行被 TabLayout 覆盖）

我将ListView 的约束更改如下，使其出现在EditText 下方

    <ListView
        android:id="@+id/listPlayers"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_marginBottom="1dp"
        app:layout_constraintBottom_toTopOf="@+id/btnApplySelection"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/txtName"
        app:layout_constraintVertical_bias="1.0" />