Android开发手记(10) 下拉菜单Spinner

1、自定义Spinner

　　首先，定义Spinner要显示的项目列表/res/values/arrays.xml

 <?xml version="1.0" encoding="utf-8"?>
 <resources>
     <string-array name="citys">
         <item>南京</item>
         <item>徐州</item>
         <item>常州</item>
     </string-array>
 </resources>

　　然后，定义一个ArrayAdapter<String>并绑定到上面定义的项目列表。

 ArrayAdapter<String> adapter = ArrayAdapter.createFromResource(
                 this, R.array.citys, android.R.layout.simple_spinner_item);
 adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);

　　其中，createFromResource()的函数原型为：

createFromResource(Context context, int textArrayResId, int textViewResId);

　　然后，将adapter绑定到spinner：

  spinner.setAdapter(adapter);

　　最后，为spinner添加一个setOnItemSelectedListener即可：

     spinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
             @Override
             public void onItemSelected(AdapterView<?> adapterView, View view, int i, long l) {
                 Toast.makeText(MainActivity.this, "position" + i + spinner.getSelectedItem().toString(),
                             Toast.LENGTH_SHORT).show();
                 }

             @Override
             public void onNothingSelected(AdapterView<?> adapterView) {
                 Toast.makeText(MainActivity.this, "unselected", Toast.LENGTH_SHORT);
             }
         });

　　完整代码为：

 public class MainActivity extends AppCompatActivity {

     private Spinner spinner;

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

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

         ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(
                 this, R.array.citys, android.R.layout.simple_spinner_item);
         adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
         spinner.setAdapter(adapter);

         spinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
             @Override
             public void onItemSelected(AdapterView<?> adapterView, View view, int i, long l) {
                 Toast.makeText(MainActivity.this, "position" + i + spinner.getSelectedItem().toString(),
                             Toast.LENGTH_SHORT).show();
                 }

             @Override
             public void onNothingSelected(AdapterView<?> adapterView) {
                 Toast.makeText(MainActivity.this, "unselected", Toast.LENGTH_SHORT);
             }
         });

     }

 }

MainActivity.java

2、动态改变Spinner

　　想动态改变Spinner的内容，需要将Spinner的内容绑定到一个Adapter上。通过增加ArrayAdapter的内容来动态改变Spinner的内容。

         ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_dropdown_item);
         adapter.add("南京");
         adapter.add("徐州");
         adapter.add("常州");
         spinner.setAdapter(adapter);

　　（1）增加一个项

　　通过在EditText输入需要增加的内容，之后单击一个Button来增加Spinner。为Button添加以下事件即可。

 btnAdd.setOnClickListener(new View.OnClickListener() {
             @Override
             public void onClick(View view) {
                 String city = editText.getText().toString();
                 for (int i = 0; i < adapter.getCount(); i++) {
                     if (city.equals(adapter.getItem(i))) {
                         Toast.makeText(MainActivity.this, "此城市已存在", Toast.LENGTH_SHORT).show();
                         return;
                     }
                 }
                 if (!city.trim().equals("")) {
                     adapter.add(city);
                     int pos = adapter.getPosition(city);
                     spinner.setSelection(pos);
                     editText.setText("");
                 }
             }
         });

　　（2）删除一个项

　　通过在Spinner选中需要删除的内容，之后单击一个Button来删除Spinner。为Button添加以下事件即可。

 btnDel.setOnClickListener(new View.OnClickListener() {
             @Override
             public void onClick(View view) {
                 if (spinner.getSelectedItem() != null) {
                     adapter.remove(spinner.getSelectedItem().toString());
                     editText.setText("");
                     if (adapter.getCount() == 0) {
                         Toast.makeText(MainActivity.this, "列表为空", Toast.LENGTH_SHORT).show();
                     }
                 }
             }
         });

3、完整代码如下：

 import android.support.v7.app.AppCompatActivity;
 import android.os.Bundle;
 import android.view.View;
 import android.widget.AdapterView;
 import android.widget.ArrayAdapter;
 import android.widget.Button;
 import android.widget.EditText;
 import android.widget.Spinner;
 import android.widget.Toast;

 public class MainActivity extends AppCompatActivity {

     private Spinner spinner;
     private EditText editText;
     private Button btnAdd;
     private Button btnDel;
     private ArrayAdapter<String> adapter;

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

         btnAdd = (Button) findViewById(R.id.btnAdd);
         btnDel = (Button) findViewById(R.id.btnDel);
         editText = (EditText) findViewById(R.id.editText);
         spinner = (Spinner) findViewById(R.id.spinner);

         adapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_dropdown_item);
         adapter.add("南京");
         adapter.add("徐州");
         adapter.add("常州");
         spinner.setAdapter(adapter);

         btnAdd.setOnClickListener(new View.OnClickListener() {
             @Override
             public void onClick(View view) {
                 String city = editText.getText().toString();
                 for (int i = 0; i < adapter.getCount(); i++) {
                     if (city.equals(adapter.getItem(i))) {
                         Toast.makeText(MainActivity.this, "此城市已存在", Toast.LENGTH_SHORT).show();
                         return;
                     }
                 }
                 if (!city.trim().equals("")) {
                     adapter.add(city);
                     int pos = adapter.getPosition(city);
                     spinner.setSelection(pos);
                     editText.setText("");
                 }
             }
         });
         btnDel.setOnClickListener(new View.OnClickListener() {
             @Override
             public void onClick(View view) {
                 if (spinner.getSelectedItem() != null) {
                     adapter.remove(spinner.getSelectedItem().toString());
                     editText.setText("");
                     if (adapter.getCount() == 0) {
                         Toast.makeText(MainActivity.this, "列表为空", Toast.LENGTH_SHORT).show();
                     }
                 }
             }
         });
         spinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
             @Override
             public void onItemSelected(AdapterView<?> adapterView, View view, int i, long l) {
                 editText.setText(adapter.getItem(i));
             }

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

             }
         });

     }

 }