我在应用程序中编程显示字,但我有错误:
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
我知道我的错误是指 CustomBaseAadpter 中的:
holder.txtWord.setText(rowItem.getword())
但我不知道如何修复。
CustomBaseAdapter.java
public class CustomBaseAdapter extends BaseAdapter {
Context context;
private List<item_row_adapter> rowItems;
public CustomBaseAdapter(Context context, List<item_row_adapter> items) {
this.context = context;
this.rowItems = items;
}
private class ViewHolder {
TextView txtWord;
TextView txtMean;
}
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder holder = null;
LayoutInflater mInflater = (LayoutInflater) context.getSystemService(Activity.LAYOUT_INFLATER_SERVICE);
if (convertView == null) {
convertView = mInflater.inflate(R.layout.list_view, null);
holder = new ViewHolder();
holder.txtWord = (TextView) convertView.findViewById(R.id.word_word);
holder.txtMean = (TextView) convertView.findViewById(R.id.mean_mean);
convertView.setTag(holder);
} else {
holder = (ViewHolder) convertView.getTag();
}
item_row_adapter rowItem = (item_row_adapter) getItem(position);
holder.txtWord.setText(rowItem.getword());
holder.txtMean.setText(rowItem.getmean());
return convertView;
}
@Override
public int getCount() {
// TODO Auto-generated method stub
return rowItems.size();
}
@Override
public Object getItem(int position) {
// TODO Auto-generated method stub
return rowItems.get(position);
}
@Override
public long getItemId(int position) {
// TODO Auto-generated method stub
return rowItems.indexOf(getItem(position));
}
}
item_row_adapter.java
public class item_row_adapter {
private String word ="";
private String mean = "";
public item_row_adapter(String word, String mean) {
this.word = word;
this.mean = mean;
}
public String getmean() {
return mean;
}
public void setmean(String mean) {
this.mean = mean;
}
public String getword() {
return word;
}
public void setword(String word) {
this.word = word;
}
public String tostring() {
return mean + "\n" + word;
}
}
vocab_1_program.java
public class vocab_1_program extends Activity implements OnItemClickListener {
private ListView listview ;
public static final String[] Word_item = new String[] { "Strawberry", "Banana", "Orange", "Mixed" };
public static final String[] Mean_word = new String[] {
"It is an aggregate accessory fruit",
"It is the largest herbaceous flowering plant", "Citrus Fruit", "Mixed Fruits" };
List<item_row_adapter> rowItems;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.vocab_1_layout);
rowItems = new ArrayList<item_row_adapter>();
for (int i = 0; i < Word_item.length; i++) {
item_row_adapter item = new item_row_adapter(Word_item[i],
Mean_word[i]);
rowItems.add(item);
}
listview = (ListView) findViewById(R.id.listview_view);
CustomBaseAdapter adapter = new CustomBaseAdapter(this, rowItems);
listview.setAdapter(adapter);
listView.setOnItemClickListener((android.widget.AdapterView.OnItemClickListener) this);
}
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
Toast toast = Toast.makeText(getApplicationContext(), "Item "
+ (position + 1) + ": " + rowItems.get(position),
Toast.LENGTH_SHORT);
toast.setGravity(Gravity.BOTTOM | Gravity.CENTER_HORIZONTAL, 0, 0);
toast.show();
}
}
word_row.xml
<TextView
android:id="@+id/word_word"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_weight="1"
android:gravity="center_horizontal"
android:text="Header"
android:textColor="@android:color/black" />
<TextView
android:id="@+id/mean_mean"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_weight="1"
android:gravity="center_horizontal"
android:text="Mean" />
vocab_1_layout.xml
<ListView
android:id="@+id/listview_view"
android:layout_width="fill_parent"
android:layout_height="fill_parent" >
</ListView>
最佳答案
您为该行添加了错误的布局。
R.layout.list_view
没有所需的 View 。 你正在拥有它
word_row.xml
在 public View getView(int position, View convertView, ViewGroup parent)
下的 CustomBaseAadpter
中,您正在膨胀没有所需 View 元素的 xml。
findViewById()
方法返回一个与 id 对应的 View 实例,并出现在展开的布局中。
由于您膨胀了错误的布局,并且该布局没有找到 View ,这就是方法 findViewById()
为 View 返回 null 的原因。
注意这一行-
holder.txtWord = (TextView) convertView.findViewById(R.id.word_word);
holder.txtMean = (TextView) convertView.findViewById(R.id.mean_mean);
因此这里 holder.txtWord= null 和 holder.txtMean=null
当您设置时调用实例 holder.txtWord
上的方法 setText()
它会抛出 NPE。
关于java - 自定义 ListView 适配器有 null NullPointerException 错误,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/31625301/