android中adapter.clear()引起的错误

最新推荐文章于 2021-05-29 10:17:38 发布

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最新推荐文章于 2021-05-29 10:17:38 发布

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分类专栏： Android学习

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本文介绍如何解决Android应用中Spinner组件无法清空数据的问题。通过使用List替代数组作为数据源，实现了对Spinner绑定数据的动态更新和清除。

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", "广州", "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();
	}
}

点击这里的Button，也就是执行onClick()之后，发生如下错误：

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<?> interface to the adapter. Example:

含义就是这里如果使用数组传递到Adapter的话，则它会将这个转化为AbstractList，而这个AbstractList是不可以修改的。

public ArrayAdapter(Context context, int resource, T[] objects) {
        init(context, resource, 0, Arrays.asList(objects));
    }

可以看到这里的源码是调用了Arrays.asList()，我们知道这个Arrays.asList()会返回一个不可修改的ArrayList，而且这个ArrayList是Arrays里面的。

正确的方式如下：

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("广州");
		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();
	}
}