在Kotlin中自定義實現回調以進行改造

Question

我最近開始使用Kotlin進行android開發，並且遇到了一些小問題，這些問題可以通過使用文檔來解決，但是使用Retrofit Callback實現時，我遇到了問題。 我在Java中使用了Retrofit回調的自定義實現：

public abstract class RemoteCallback<T> implements Callback<T> {
@Override
public final void onResponse(Call<T> call, Response<T> response) {

    switch (response.code()) {
        case HttpsURLConnection.HTTP_OK:
        case HttpsURLConnection.HTTP_CREATED:
        case HttpsURLConnection.HTTP_ACCEPTED:
        case HttpsURLConnection.HTTP_NOT_AUTHORITATIVE:
            if (response.body() != null) {
                onSuccess(response.body());
            }
            break;
        case HttpURLConnection.HTTP_UNAUTHORIZED:
            onUnauthorized();
            break;
        default:
            onFailed(new Throwable("Default " + response.code() + " " + response.message()));
    }
}

@Override
public final void onFailure(Call<T> call, Throwable t) {
    onFailed(t);
}

public abstract void onSuccess(T responseBody);

public abstract void onUnauthorized();

public abstract void onFailed(Throwable throwable);}

我在Kotlin Project中使用了相同的類，該類將Java代碼轉換為Kotlin代碼

abstract class RemoteCallback<T> : Callback<T> {
override fun onResponse(call: Call<T>, response: Response<T>) {

    when (response.code()) {
        HttpsURLConnection.HTTP_OK,
        HttpsURLConnection.HTTP_CREATED,
        HttpsURLConnection.HTTP_ACCEPTED,
        HttpsURLConnection.HTTP_NOT_AUTHORITATIVE ->
            if (response.body() != null)
            onSuccess(response.body())
        HttpURLConnection.HTTP_UNAUTHORIZED -> onUnauthorized()
        else -> onFailed(Throwable("Default " + response.code() + " " + response.message()))
    }
}

override fun onFailure(call: Call<T>, t: Throwable) {
    onFailed(t)
}

abstract fun onSuccess(responseBody: T)

abstract fun onUnauthorized()

abstract fun onFailed(throwable: Throwable)}

問題是當我調用onSucess（response.body（））時，它說“不可能強制轉換為'T'，因為'response.body（）'是一個復雜的表達式” 請指導我如何解決它

Answer 1

您正在將Nullable值作為參數發送給NonNull函數。 因此，您遇到了這個問題。 您可以像這樣：

interface RemoteCallback<T> : Callback<T> {
    override fun onResponse(call: Call<T>?, response: Response<T>?) {
        when (response?.code()) {
            HttpsURLConnection.HTTP_OK,    
            HttpsURLConnection.HTTP_CREATED,
            HttpsURLConnection.HTTP_ACCEPTED,
            HttpsURLConnection.HTTP_NOT_AUTHORITATIVE ->
                response.body()?.apply { onSuccess(this) }
            HttpURLConnection.HTTP_UNAUTHORIZED -> onUnauthorized()
            else -> onFailed(Throwable("Default " + response?.code() + " " + response?.message()))
        }
    }

    override fun onFailure(call: Call<T>?, t: Throwable?) {
        // handle error mechanism
        t?.apply { onFailed(this) }    
    }
    fun onSuccess(responseBody: T)
    fun onUnauthorized()
    fun onFailed(throwable: Throwable)
}

或者，您可以只使用onSuccess(responseBody: T?) ，您的代碼應該可以工作

Answer 2

我的項目有一個非常相似的實現。 嘗試按照

abstract class RemoteCallback: Callback<ResponseBody> {
    override fun onFailure(call: Call<ResponseBody>?, t: Throwable?) {
        onFailed(t)
    }

    override fun onResponse(call: Call<ResponseBody>?, response: Response<ResponseBody>?) {
        when (response.code()) {
            HttpsURLConnection.HTTP_OK,
            HttpsURLConnection.HTTP_CREATED,
            HttpsURLConnection.HTTP_ACCEPTED,
            HttpsURLConnection.HTTP_NOT_AUTHORITATIVE ->
                if (response.body() != null)
                onSuccess(response.body())
            HttpURLConnection.HTTP_UNAUTHORIZED -> onUnauthorized()
            else -> onFailed(Throwable("Default " + response.code() + " " + response.message()))
        }
    }

    abstract fun onUnauthorized()

    abstract fun onFailed(throwable: Throwable)
}

對我來說很好