我的微调器的动作有一点问题

Question

我想在我的spinner中添加一些操作（正如您在下面的代码中看到的那样，我添加了一些Toasts）。

主要活动.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，实际上这段代码工作正常，但是如果我打开应用程序，第一个 Toast（带有文本"Item 1"）已经可见。但我不想这样。那么，我需要做什么，这不会发生？

提前感谢！

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)  {

    }
}

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();
}

Answer 3

不幸的是，谷歌没有提供在开始时具有"null"值的功能。您可以查看此链接以获取更多详细信息。希望它有帮助。:)