我的下拉列表控件（spinner）的某个操作出现了一些问题。

Question

我想为我的spinner添加一些操作（如您在下面的代码中所看到的，我添加了一些Toasts）。

MainActivity.java：

public class MainActivity extends Activity implements AdapterView.OnItemSelectedListener {

    String[] items = {"Item 1", "Item 2", "Item 3", "Item 4", "Item 5"};

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Spinner spinner1 = (Spinner) findViewById(R.id.spinner1);
        spinner1.setOnItemSelectedListener(this);

        ArrayAdapter AA = new ArrayAdapter(this, android.R.layout.simple_spinner_item, items);

        AA.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        spinner1.setAdapter(AA);
    }

    @Override
    public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {

        String selectedItem = parent.getItemAtPosition(position).toString();
        if (selectedItem.equals("Item 1")) {
            Toast.makeText(getApplicationContext(), "Item 1", Toast.LENGTH_LONG).show();
        }

        String selectedItem2 = parent.getItemAtPosition(position).toString();
        if (selectedItem.equals("Item 2")) {
            Toast.makeText(getApplicationContext(), "Item 2", Toast.LENGTH_LONG).show();
        }

        String selectedItem3 = parent.getItemAtPosition(position).toString();
        if (selectedItem.equals("Item 3")) {
            Toast.makeText(getApplicationContext(), "Item 3", Toast.LENGTH_LONG).show();
        }

        String selectedItem4 = parent.getItemAtPosition(position).toString();
        if (selectedItem.equals("Item 4")) {
            Toast.makeText(getApplicationContext(), "Item 4", Toast.LENGTH_LONG).show();
        }

        String selectedItem5 = parent.getItemAtPosition(position).toString();
        if (selectedItem.equals("Item 5")) {
            Toast.makeText(getApplicationContext(), "Item 5", Toast.LENGTH_LONG).show();
        }
    }

    @Override
    public void onNothingSelected(AdapterView<?> parent) {

    }
}

activity_main.xml:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <Spinner
        android:id="@+id/spinner1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="89dp"></Spinner>
</RelativeLayout>

所以，实际上这段代码运行良好，但是如果我打开应用程序，第一个Toast（文本为“Item 1”）已经可见。但是我不想要那样。那么，我需要做什么才能避免这种情况发生？

提前感谢！

- Piezord

Answer 1

试试这个

public class MainActivity extends Activity  implements AdapterView.OnItemSelectedListener{

String[] items = { "Item 1", "Item 2", "Item 3", "Item 4", "Item 5" };
boolean app_started = true;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main); 

    Spinner spinner1 = (Spinner) findViewById(R.id.spinner1);
    spinner1.setOnItemSelectedListener(this);

    ArrayAdapter AA = new ArrayAdapter(this, android.R.layout.simple_spinner_item, items);

    AA.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
    spinner1.setAdapter(AA);

}

    @Override
    public void onItemSelected(AdapterView parent, View view, int position, long id) {

        String selectedItem = parent.getItemAtPosition(position).toString();
  if(!app_started )
{


        if(selectedItem.equals("Item 1")) {         
            Toast.makeText(getApplicationContext(), "Item 1", Toast.LENGTH_LONG).show();
        }

        String selectedItem2 = parent.getItemAtPosition(position).toString();
        if(selectedItem.equals("Item 2")) {         
            Toast.makeText(getApplicationContext(), "Item 2", Toast.LENGTH_LONG).show();
        }

        String selectedItem3 = parent.getItemAtPosition(position).toString();
        if(selectedItem.equals("Item 3")) {         
            Toast.makeText(getApplicationContext(), "Item 3", Toast.LENGTH_LONG).show();
        }

        String selectedItem4 = parent.getItemAtPosition(position).toString();
        if(selectedItem.equals("Item 4")) {         
            Toast.makeText(getApplicationContext(), "Item 4", Toast.LENGTH_LONG).show();
        }

        String selectedItem5 = parent.getItemAtPosition(position).toString();
        if(selectedItem.equals("Item 5")) {         
            Toast.makeText(getApplicationContext(), "Item 5", Toast.LENGTH_LONG).show();
        }

 }
   app_started = false;

    }

    @Override
    public void onNothingSelected(AdapterView parent)  {


    }
}

- Sush

---

非常感谢！运行良好！ :) - Piezord

哦，你是说要点赞你的回答，好的。;) 很抱歉，但在我获得15个声望之前，我不能点赞！:( - Piezord

立即查看您的状态。 - Sush

Answer 2

试试这个 -

String selectedItem = parent.getItemAtPosition(position).toString();
if(selectedItem.equals("Item 1")) {         
Toast.makeText(getApplicationContext(), "Item 1", Toast.LENGTH_LONG).show();
}
else if(selectedItem.equals("Item 2")) {         
Toast.makeText(getApplicationContext(), "Item 2", Toast.LENGTH_LONG).show();
}
else if(selectedItem.equals("Item 3")) {         
Toast.makeText(getApplicationContext(), "Item 3", Toast.LENGTH_LONG).show();
}
else if(selectedItem.equals("Item 4")) {         
Toast.makeText(getApplicationContext(), "Item 4", Toast.LENGTH_LONG).show();
}
else if(selectedItem.equals("Item 5")) {         
Toast.makeText(getApplicationContext(), "Item 5", Toast.LENGTH_LONG).show();
}

- Kanwaljit Singh

---

也尝试了你的建议。虽然它没有解决我的问题，但它让我的代码看起来更好、更容易理解！;) 也谢谢你！:) - Piezord

Answer 3

很遗憾，谷歌还没有提供在开头使用“null”值的功能。您可以查看此链接以获取更多详细信息。希望对您有所帮助。 :)

- Srikanth R