Android “活动”中未显示文本和图像的自定义ListView
我对Android相当陌生,正在尝试创建一个基于自定义适配器的Android “活动”中未显示文本和图像的自定义ListView,android,android-listview,android-adapter,Android,Android Listview,Android Adapter,我对Android相当陌生,正在尝试创建一个基于自定义适配器的ListView,其中包含ImageView和TextView 当我尝试运行我的应用程序时,它似乎不会将列表视图显示在屏幕上。不过也没有例外。也许我错过了一些非常明显的东西。如果有人可以查看我的代码,那就太好了: MyActivity.java: public class MyActivity extends Activity { public static final String[] countries = new St
ListView
,其中包含ImageView
和TextView
当我尝试运行我的应用程序时,它似乎不会将列表视图
显示在屏幕上。不过也没有例外。也许我错过了一些非常明显的东西。如果有人可以查看我的代码,那就太好了:
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);
}
}
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;
}
线性布局的方向应为垂直
。默认值为水平
。加
android:orientation="vertical"
到包含列表视图的线性布局
<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">
这可能会通过可视化解决您的问题。
另一方面,您可以改变一些事情来提高性能
- 在布局中,您应该提供
0dip
作为高度,因为您提供的是重量。这将在“onLayout
”时间帮助框架李>
ArrayAdapter
具有getItem()
的具体实现。您不需要再次重写它,因为您已经将数据集提供给了超类
- 您以错误的方式使用了
ViewHolder
图案。当convertView为空时,您应该实例化一次ViewHolder
,查找视图(正如您已经做的那样),并调用convertView.setTag(viewHolderInstance)
在我的自定义适配器类下面的操作系统中,引用它并这样做,它肯定会工作
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;
}
}
在activity\u我的最上面的linearlayout
应该具有android:orientation=“vertical”
属性
在您的行布局中
父布局是水平线布局
和android:layout\u width
对于ImageView
和TextView
都是fill\u parent
,只有ImageView
可见,如LinearLayout
子项逐个线性放置。如下更改rowlayout
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:gravity="center_vertical"
android:padding="8dp"
android:orientation="horizontal" >
<ImageView
android:id="@+id/countryImage"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:paddingRight="10dp" />
<TextView
android:id="@+id/countryName"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="countryName" />
</LinearLayout>
public void updateAdapter(MyListObject _newObject){
objectList.add(_newObject);
adapter.notifyDataSetChanged();
}
屏幕截图:
确保图像的宽度和高度未设置为与约束匹配。另外,尝试在主活动中更新适配器,如下所示
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:gravity="center_vertical"
android:padding="8dp"
android:orientation="horizontal" >
<ImageView
android:id="@+id/countryImage"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:paddingRight="10dp" />
<TextView
android:id="@+id/countryName"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="countryName" />
</LinearLayout>
public void updateAdapter(MyListObject _newObject){
objectList.add(_newObject);
adapter.notifyDataSetChanged();
}
您必须在自定义适配器中调用getCount方法。并且必须在其中返回数组大小。@pratik getCount已在超类中重写。非常感谢!adapter getView方法中的if子句让我非常困惑。。。
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:gravity="center_vertical"
android:padding="8dp"
android:orientation="horizontal" >
<ImageView
android:id="@+id/countryImage"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:paddingRight="10dp" />
<TextView
android:id="@+id/countryName"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="countryName" />
</LinearLayout>
public class MySimpleArrayAdapter extends ArrayAdapter<MyListObject> {
private final Context context;
private final List<MyListObject> values;
private int resourceID;
public MySimpleArrayAdapter(Context context, int resourceID, List<MyListObject> values) {
super(context, resourceID, values);
this.context = context;
this.resourceID = resourceID;
this.values = values;
}
private class ViewHolder {
ImageView imageView;
TextView textView;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder holder;
if (convertView == null) {
LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
convertView = inflater.inflate(resourceID, null);
holder = new ViewHolder();
holder.textView = (TextView) convertView.findViewById(R.id.countryName);
holder.imageView = (ImageView) convertView.findViewById(R.id.countryImage);
convertView.setTag(holder);
} else {
holder = (ViewHolder) convertView.getTag();
}
MyListObject rowItem = (MyListObject) values.get(position);
holder.textView.setText(rowItem.getCountry());
holder.imageView.setImageResource(rowItem.getImage());
return convertView;
}
}
public void updateAdapter(MyListObject _newObject){
objectList.add(_newObject);
adapter.notifyDataSetChanged();
}