从Android Spinner获取枚举值 [英] Getting an enumerated value out of an Android Spinner

问题描述

我下面写了一个类，让我从Android Spinner中获得一个枚举值。

getValue中有两行（）这两个都不编译。

我该怎么做？

  public class EnumSpinnerListener< T extends Enum>实现AdapterView.OnItemSelectedListener {
 private String mValue = null; 
 
 public EnumSpinnerListener（AdapterView<？> adapterView）{
 adapterView.setOnItemSelectedListener（this）; 
 
 
 @Override 
 public void onItemSelected（AdapterView<？> adapterView，View view，int i，long l）{
 mValue = adapterView.getItemAtPosition ⅰ）的ToString（）; 
} 
 
 @Override 
 public void onNothingSelected（AdapterView<？> adapterView）{
 // do nothing 
} 
 
 public T getValue（）{
 return Enum.valueOf（T.class，mValue）; //不能从类型变量中选择
返回T.valueOf（mValue）;枚举中的valueOf（java.lang.Class< T>，String）不能应用于（java.lang.String）
} 
} 
  / pre> 
 
解决方案
由于类型擦除， T 在运行时没有意义，这就是为什么表达式 T.class 是非法的。解决方法是引用类< T> 实例：
  public类EnumSpinnerListener< T扩展枚举< T>> //注意这里的修正
实现了AdapterView.OnItemSelectedListener {
 
 private final Class< T>类型; 
 
 private String mValue = null; 
 
 public EnumSpinnerListener（Class< T> type，AdapterView<？> adapterView）{
 this.type = type; 
 adapterView.setOnItemSelectedListener（this）; 
} 
 
 public T getValue（）{
 return Enum.valueOf（type，mValue）; 
} 
} 
  
 
I've written the class below to let me get an enumerated value out of an Android Spinner.

There are two lines in getValue() neither of which compile.

How should I do this?
public class EnumSpinnerListener<T extends Enum> implements AdapterView.OnItemSelectedListener {
    private String mValue = null;

    public EnumSpinnerListener(AdapterView<?> adapterView) {
        adapterView.setOnItemSelectedListener(this);
    }

    @Override
    public void onItemSelected(AdapterView<?> adapterView, View view, int i, long l) {
        mValue = adapterView.getItemAtPosition(i).toString();
    }

    @Override
    public void onNothingSelected(AdapterView<?> adapterView) {
        // do nothing
    }

    public T getValue() {
        return Enum.valueOf(T.class, mValue); // cannot select from a type variable
        return T.valueOf(mValue); // valueOf(java.lang.Class<T>, String) in enum cannot be applied to (java.lang.String)
    }
}

解决方案
Due to type erasure, T will have no meaning at runtime, which is why the expression T.class is illegal. The workaround is to reference a Class<T> instance:
public class EnumSpinnerListener<T extends Enum<T>> // note the correction here
implements AdapterView.OnItemSelectedListener {

    private final Class<T> type;

    private String mValue = null;

    public EnumSpinnerListener(Class<T> type, AdapterView<?> adapterView) {
        this.type = type;
        adapterView.setOnItemSelectedListener(this);
    }

    public T getValue() {
        return Enum.valueOf(type, mValue);
    }
}


                        
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