Getting an enumerated value out of an Android Spinner

问题

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)
    }
}

回答1:

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);
    }
}

来源：https://stackoverflow.com/questions/17784067/getting-an-enumerated-value-out-of-an-android-spinner

标签

java

android

generics

enums

spinner