Android listview根本不可见
我面临着列表视图的问题,有一个自定义的卡片布局视图应该出现在列表视图中。这是主FirstActivity.java文件,包括适配器类,然后是activity_first.xml、card_layout.xml和屏幕截图。我的问题是,当我运行此应用程序时,它安装成功,但列表视图根本不可见:Android listview根本不可见,android,listview,adapter,android-cardview,Android,Listview,Adapter,Android Cardview,我面临着列表视图的问题,有一个自定义的卡片布局视图应该出现在列表视图中。这是主FirstActivity.java文件,包括适配器类,然后是activity_first.xml、card_layout.xml和屏幕截图。我的问题是,当我运行此应用程序时,它安装成功,但列表视图根本不可见: public class FirstActivity extends AppCompatActivity { private Toolbar toolbar; private ListView
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;
}
}
}
以下是第一个_activity.xml:
<?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>
在适配器
构造函数中,某些类变量的名称与参数的名称相同。所以,所有的操作都只对参数进行,它使这个的大小为0。titleArray
将为0,然后getCount()
方法始终返回0,然后在活动中不显示任何项目。因此,必须使用this
来引用类变量。按以下方式修改您的代码:
public adapter(Context context, String[] titleArray, String[] descriptionArray) {
mContext = context;
this.titleArray = titleArray;
this.descriptionArray = descriptionArray;
layoutInflater = LayoutInflater.from(context);
}
我正在检查您的代码,这很好,但您使用了太多的try-catch,所以您无法理解这个问题。试着分享你的一些想法log@RadeshTry/catch很好,不要建议不要捕获异常。@INagwani。我在您的适配器类中发现了一个bug,如我的回答中所述。你的程序现在运行顺利吗?我也是新安卓,所以我想帮助你通过它来提高我的技能。@Radesh感谢你的建议,但一开始我没有发现异常,安装后不久应用程序由于“NullPointerException”而崩溃。这很有魅力,因为这个错误挣扎了将近一天,我真的很感谢你的努力,非常感谢你。
<resources>
<string name="app_name">TimeTable</string>
<string-array name="Main">
<item>TimeTable</item>
<item>Subjects</item>
<item>Faculty</item>
<item>Resources</item>
</string-array>
<string-array name="Desc">
<item>desc_1</item>
<item>desc_2</item>
<item>desc_3</item>
<item>desc_4</item>
</string-array>
</resources>
public adapter(Context context, String[] titleArray, String[] descriptionArray) {
mContext = context;
this.titleArray = titleArray;
this.descriptionArray = descriptionArray;
layoutInflater = LayoutInflater.from(context);
}