Question

我对Android很新，我正在尝试根据自定义适配器创建ListView ImageView和TextView。

当我尝试运行我的应用程序时，似乎不会将ListView放在屏幕上。不过没有例外。也许我错过了一些非常明显的东西。如果有人能查看我的代码会很棒：

MyActivity.java：

public class MyActivity extends Activity {

    public static final String[] countries = new String[] {"Germany", "USA", "Great Britain", "Japan", "Korea"};
    public static final int[] images = new int[]{R.drawable.de, R.drawable.us, R.drawable.kr, R.drawable.jp, R.drawable.kr};
    ListView listView;
    List<MyListObject> values;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_my);
        TextView textView = (TextView) findViewById(R.id.textView);

        values = new ArrayList<MyListObject>();
        for (int i = 0; i < countries.length; i++) {
            MyListObject item = new MyListObject();
            item.setCountry(countries[i]);
            item.setImage(images[i]);
            values.add(item);
        }

        listView = (ListView) findViewById(R.id.list);
        MySimpleArrayAdapter adapter = new MySimpleArrayAdapter(this, R.layout.rowlayout, values);
        listView.setAdapter(adapter);

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.my, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }
}

MySimpleArrayAdapter.java：

public class MySimpleArrayAdapter extends ArrayAdapter<MyListObject> {
    private final Context context;
    private final List<MyListObject> values;

    public MySimpleArrayAdapter(Context context, int resourceID, List<MyListObject> values) {
        super(context, resourceID, values);
        this.context = context;
        this.values = values;
    }

    private class ViewHolder {
        ImageView imageView;
        TextView textView;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ViewHolder holder;
        MyListObject rowItem = getItem(position);

        LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        if (convertView == null) {
            convertView = inflater.inflate(R.layout.rowlayout, null);


        } else {
            holder = (ViewHolder) convertView.getTag();
        }
        holder = new ViewHolder();
        holder.textView = (TextView) convertView.findViewById(R.id.countryName);
        holder.imageView = (ImageView) convertView.findViewById(R.id.countryImage);


        holder.textView.setText(rowItem.getCountry());
        holder.imageView.setImageResource(rowItem.getImage());

        return convertView;
    }

    @Override
    public MyListObject getItem(int position) {
        return values.get(position);
    }

}

activity_my.xml：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin"
    tools:context=".MyActivity">

    <TextView
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:id="@+id/textView"/>

    <ListView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/list"
        android:layout_weight="1" />
</LinearLayout>

rowlayout.xml：

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="horizontal" android:layout_width="fill_parent"
    android:layout_height="wrap_content" android:gravity="center_vertical" >

    <ImageView
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:paddingRight="10dp"
        android:id="@+id/countryImage" />
    <TextView
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:id="@+id/countryName"
        android:text="@+id/countryName" />

</LinearLayout>

MyListObject.java：

public class MyListObject {
    private int image;
    private String country;

    public int getImage() {
        return image;
    }

    public void setImage(int image) {
        this.image = image;
    }

    public String getCountry() {
        return country;
    }

    public void setCountry(String country) {
        this.country = country;
    }
}

Answer 1

在activity_my's最顶层linearlayout应该有android:orientation="vertical"属性

在rowlayout父级布局中，Horizontal LinearLayout和android:layout_width ImageView和TextView都是fill_parent。因此，仅{{1} } {} {}} {}} {}} {}} {}}

ImageView

您还需要更改LinearLayout

<强> MySimpleArrayAdapter

rowlayout

屏幕截图：

enter image description here

Answer 2

试试这个：

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

    LayoutInflater inflater = (LayoutInflater) context
            .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    View rowView = inflater.inflate(layout, parent, false);

    //...

    return rowView;

}

Answer 3

LinearLayout的方向应为vertical。默认值为horizontal。添加

android:orientation="vertical"

包含LinearLayout

的ListView

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin"
tools:context=".MyActivity">

这可能会解决您使用可视化的问题。另一方面，您可以更改一些内容以提高性能。

在你的布局中，你应该提供0dip作为身高，因为你提供了重量。这将有助于“onLayout”时间的框架。
ArrayAdapter具有getItem()的具体实现。您不需要再次覆盖它，因为您已经将数据集提供给超类
您正以错误的方式使用ViewHolder模式。您应该实例化ViewHolder一次，当convertView为null时，查找视图（就像您已经做过的那样）并调用convertView.setTag(viewHolderInstance)，

Answer 4

下面是我的自定义适配器类，请参考它并按照这种方式执行，它肯定会有效。

private class EfficientAdapter extends BaseAdapter {

        private LayoutInflater mInflater;
        private Context context;
        JSONArray array;
        private Bitmap imageBitmap = null;

        public EfficientAdapter(Context context) {
            mInflater = LayoutInflater.from(context);
            this.context = context;
        }

        @Override
        public int getCount() {
            return data.size();
        }

        @Override
        public Object getItem(int arg0) {
            return null;
        }

        @Override
        public long getItemId(int position) {
            return 0;
        }

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

            final ViewHolder holder;

            if (convertView == null) {
                convertView = mInflater.inflate(R.layout.featured_item, null);
                holder = new ViewHolder();
                holder.txtTitle = (TextView) convertView.findViewById(R.id.txtTitle);
                holder.txtAuthorName = (TextView) convertView.findViewById(R.id.txtAuthorName);
                holder.txtDescription = (TextView) convertView.findViewById(R.id.txtDescription);
                convertView.setTag(holder);
            } else {
                holder = (ViewHolder) convertView.getTag();
            }

            holder.txtTitle.setText(data.get(position).get("article_title"));
            holder.txtAuthorName.setText(data.get(position).get("author_name"));
            holder.txtDescription.setText(data.get(position).get("article_text"));





            return convertView;
        }

        class ViewHolder {
            TextView txtTitle;
            TextView txtAuthorName;
            TextView txtDescription;
        }

    }

Answer 5

确保未将图像宽度和高度设置为与约束匹配。另外，尝试更新主活动中的适配器，如此

public void updateAdapter(MyListObject _newObject){
    objectList.add(_newObject);
    adapter.notifyDataSetChanged();
}

自定义ListView，文本和图像未显示在“活动”中

5 个答案: