Question

我在列表视图中遇到问题，有一个自定义卡片布局视图，该视图应出现在列表视图中。这是主要的 FirstActivity.java 文件，包括适配器类，其后是 activity_first.xml ， card_layout.xml 和截屏。我的问题是，当我运行此应用程序时，它安装成功，但列表视图完全不可见：

txt = str(input("Text: ")).upper()
ntxt = ""

for char in txt:
    if char in abc:
        ntxt += abc[char]
    else:
        ntxt += char

print("New string:", ntxt)

这是first_activity.xml：

public class FirstActivity extends AppCompatActivity {

    private Toolbar toolbar;
    private ListView listView;


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

            setupUIViews();
            toolbarSettings();
            setupListView();
        }
        catch (java.lang.NullPointerException exception) {
            exception.printStackTrace();
        }

    }

    private void setupUIViews () {

        try {
            toolbar = (Toolbar) findViewById(R.id.ToolbarMain);
            listView = (ListView) findViewById(R.id.lv_main);
        }
        catch (java.lang.NullPointerException exception) {
            exception.printStackTrace();
        }
    }

    private void toolbarSettings() {

        setSupportActionBar(toolbar);
        getSupportActionBar().setTitle("TimeTable");

    }

        private void setupListView () {

            try {

                String[] title = getResources().getStringArray(R.array.Main);
                String[] description = getResources().getStringArray(R.array.Desc);

                adapter adapter = new adapter(this, title, description);
                listView.setAdapter(adapter);

            } catch (java.lang.NullPointerException exception) {
                exception.printStackTrace();
            }
        }

    public class adapter extends BaseAdapter {

        private Context mContext;
        private LayoutInflater layoutInflater;
        private TextView title, description;
        private String[] titleArray;
        private String[] descriptionArray;
        private ImageView imageView;

        public adapter(Context context, String[] titleArray, String[] descriptionArray) {

            mContext = context;
            titleArray = titleArray;
            descriptionArray = descriptionArray;
            layoutInflater = LayoutInflater.from(context);

        }


        @Override
        public int getCount() {
            int length = 0;
            try {
                length = titleArray.length;
            }
            catch (java.lang.NullPointerException exception) {
                exception.printStackTrace();
            }

            return length;
        }

        @Override
        public Object getItem(int position) {
            return titleArray[position];
        }

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

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {

            if(convertView == null ) {
                convertView = layoutInflater.inflate(R.layout.card_layout, null);
            }

            title = (TextView)convertView.findViewById(R.id.tv_heading);
            description = (TextView)convertView.findViewById(R.id.tv_desc);
            imageView = (ImageView)convertView.findViewById(R.id.iv_main);

            title.setText(titleArray[position]);
            description.setText(descriptionArray[position]);

            if (titleArray[position].equalsIgnoreCase("TimeTable")) {
                imageView.setImageResource(R.drawable.timetable);
            }
            else if (titleArray[position].equalsIgnoreCase("Subjects")) {
                imageView.setImageResource(R.drawable.calender);
            }
            else if (titleArray[position].equalsIgnoreCase("Faculty")) {
                imageView.setImageResource(R.drawable.contact);
            }
            else
                imageView.setImageResource(R.drawable.settings);

            return convertView;
        }

    }

}

这是card_layout.xml文件：-

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

    <android.support.v7.widget.Toolbar
        android:layout_width="match_parent"
        android:layout_height="?android:attr/actionBarSize"
        android:background="@color/colorPrimary"
        android:id="@+id/ToolbarMain">
    </android.support.v7.widget.Toolbar>

    <ListView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_marginLeft="10dp"
        android:layout_marginRight="10dp"
        android:layout_marginTop="10dp"
        android:layout_marginBottom="10dp"
        android:layout_below="@+id/ToolbarMain"
        android:divider="@null"
        android:id="@+id/lv_main">
    </ListView>
</RelativeLayout>

最后，这是我的strings.xml：-

<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="@color/colorAccent"
    android:elevation="4dp">

    <RelativeLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content">

        <ImageView
            android:layout_width="85dp"
            android:layout_height="105dp"
            android:layout_marginStart="10dp"
            android:id="@+id/iv_main"/>

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_toEndOf="@id/iv_main"
            android:textStyle="bold"
            android:layout_marginBottom="5dp"
            android:text="IshaanNagwani"
            android:textSize="20sp"
            android:id="@+id/tv_heading"/>

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="IshaanNagwani"
            android:textSize="16sp"
            android:layout_below="@id/tv_heading"
            android:layout_toEndOf="@id/iv_main"
            android:id="@+id/tv_desc"/>

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_below="@id/tv_desc"
            android:layout_alignBottom="@id/iv_main"
            android:layout_alignParentRight="true"
            android:layout_marginTop="29sp"
            android:text="IshaanNagwani"
            android:textAlignment="center"
            android:textSize="12sp"
            android:id="@+id/tv_third"/>

    </RelativeLayout>

</android.support.v7.widget.CardView>

我是android的新手，这是我的第一篇文章。我正在使用ListView。显然我做错了什么，但我不知道这是什么。完全安装后，这是该应用程序的屏幕截图：

Answer 1

在{"id":"1,"name:"First",...}构造函数中，某些类变量的名称与参数的名称相同。因此，将仅对参数进行所有操作，这将使adapter的大小为零，然后this.titleArray方法始终返回0，那么活动中不会出现任何项目。因此，您必须使用getCount()来引用类变量。修改您的代码，如下所示：

this

列表视图根本不可见

1 个答案: