微调器在 Android 中不工作

Question

微调器不工作。这是我的代码：

public class second extends Activity{   
    Spinner spin;
    String[] str;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.second);        
        spin = (Spinner) findViewById(R.id.spin);
        str = new String[] {"bike","car"};      
        spin.setAdapter(new ArrayAdapter<CharSequence>(this, android.R.layout.simple_dropdown_item_1line, str));    

        spin.setOnItemClickListener(new OnItemClickListener() {

            public void onItemClick(AdapterView<?> adapter, View view, int pos,
                long id) {
            // TODO Auto-generated method stub

            String data= spin.getItemAtPosition(pos).toString();
            Toast.makeText(second.this, data, Toast.LENGTH_SHORT).show();
               }    
        });
    }
}

Answer 1

您犯的唯一错误是您设置了不同的事件侦听器。

侦听器 OnItemClickListener 用于 ListView。

对于 Spinner 您必须设置 < code>OnItemSelectedListener ..

尝试将 OnItemClickListener 替换为 setOnItemSelectedListener，如下所示：

spin.setOnItemSelectedListener (new OnItemSelectedListener() {

    public void onItemClick(AdapterView<?> adapter, View view, int pos,
            long id) {
        // TODO Auto-generated method stub

        String data= spin.getItemAtPosition(pos).toString();
        Toast.makeText(second.this, data, Toast.LENGTH_SHORT).show();
    }

});

Answer 2

问题出在这里，

 spin.setOnItemClickListener(new OnItemClickListener() {

    public void onItemClick(AdapterView<?> adapter, View view, int pos,
            long id) {
        // TODO Auto-generated method stub

        String data= spin.getItemAtPosition(pos).toString();
        Toast.makeText(second.this, data, Toast.LENGTH_SHORT).show();
    }

});

尝试替换如下，

 spin.OnItemSelectedListener (new OnItemSelectListener() {

    public void onItemSelect(AdapterView<?> adapter, View view, int pos,
            long id) {
        // TODO Auto-generated method stub

        String data= spin.getItemAtPosition(pos).toString();
        Toast.makeText(second.this, data, Toast.LENGTH_SHORT).show();
    }

});

Answer 3

这是 oncreate() 方法中的问题：

spin = (Spinner) findViewById(R.id.spin);

您将结果分配给 spinner，它是此处的局部变量/引用。 main.spinner 类字段仍然为空。这就是为什么在calculate()方法中出现NullPointerException的原因。

将上面的行替换为：

this.spin = (Spinner) findViewById(R.id.spin);

ArrayAdapter<String> adapter = new ArrayAdapter<String> (this, android.R.layout.simple_spinner_item,androidBooks);
spin.setAdapter(adapter);

Answer 4

试试这个

 spinner = (Spinner) findViewById(R.id.spinner);
 List<String> categories = new ArrayList<String>();
    categories.add("--Qualification--");
    categories.add("High School");
    categories.add("Higher Secondary/PUC");
    categories.add("Diploma");
    categories.add("Degree");
    categories.add("Master Degree");


    ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, 
    R.layout.spinnertext, categories);
    adapter.setDropDownViewResource(android.R.layout.select_dialog_item);
    spinner.setAdapter(adapter);

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