android中adapter.clear()引起的錯誤
阿新 • • 發佈：2019-01-30
public class MainActivity extends Activity implements OnClickListener { ArrayAdapter<String> adapter; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.paomadeng); Spinner spinner = (Spinner) findViewById(R.id.spinner); String[] strArray = new String[]{"杭州","上海", "南京", "北京", "廣州", "深圳"}; adapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_dropdown_item, strArray); spinner.setAdapter(adapter); spinner.setOnItemSelectedListener(new OnItemSelectedListener() { @Override public void onItemSelected(AdapterView<?> parent, View view, int position, long id) { System.out.println(adapter.getItem(position)); } @Override public void onNothingSelected(AdapterView<?> parent) { System.out.println("nothing selected"); } }); Button btn = (Button) findViewById(R.id.btn); btn.setOnClickListener(this); } @Override public void onClick(View v) { adapter.clear(); } }
點選這裡的Button，也就是執行onClick()之後，發生如下錯誤：
02-16 13:50:21.062: E/AndroidRuntime(29353): FATAL EXCEPTION: main 02-16 13:50:21.062: E/AndroidRuntime(29353): java.lang.UnsupportedOperationException 02-16 13:50:21.062: E/AndroidRuntime(29353): at java.util.AbstractList.remove(AbstractList.java:638) 02-16 13:50:21.062: E/AndroidRuntime(29353): at java.util.AbstractList$SimpleListIterator.remove(AbstractList.java:75) 02-16 13:50:21.062: E/AndroidRuntime(29353): at java.util.AbstractList.removeRange(AbstractList.java:658) 02-16 13:50:21.062: E/AndroidRuntime(29353): at java.util.AbstractList.clear(AbstractList.java:466) 02-16 13:50:21.062: E/AndroidRuntime(29353): at android.widget.ArrayAdapter.clear(ArrayAdapter.java:258)
http://stackoverflow.com/questions/10504353/adapter-clear-crashes-android-app
You are probably getting an UnsupportedOperationException,
right? This is because the adapters get initialised with an array of objects, which it interally converts to an AbstractList,
which cannot be modified.
To solve your problem, you simply need to feed something that implements the List<?>
public ArrayAdapter(Context context, int resource, T[] objects) {
init(context, resource, 0, Arrays.asList(objects));
}可以看到這裡的原始碼是呼叫了Arrays.asList()，我們知道這個Arrays.asList()會返回一個不可修改的ArrayList，而且這個ArrayList是Arrays裡面的。
正確的方式如下：
public class MainActivity extends Activity implements OnClickListener {
ArrayAdapter<String> adapter;
List<String> datas = new ArrayList<String>();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.paomadeng);
Spinner spinner = (Spinner) findViewById(R.id.spinner);
datas.add("杭州");
datas.add("上海");
datas.add("南京");
datas.add("北京");
datas.add("廣州");
datas.add("深圳");
adapter = new ArrayAdapter<String>(this,
android.R.layout.simple_spinner_dropdown_item, datas);
spinner.setAdapter(adapter);
spinner.setOnItemSelectedListener(new OnItemSelectedListener() {
@Override
public void onItemSelected(AdapterView<?> parent, View view,
int position, long id) {
System.out.println(adapter.getItem(position));
}
@Override
public void onNothingSelected(AdapterView<?> parent) {
System.out.println("nothing selected");
}
});
Button btn = (Button) findViewById(R.id.btn);
btn.setOnClickListener(this);
}
@Override
public void onClick(View v) {
datas.clear();
adapter.notifyDataSetChanged();
}
}