Question

我有两个从AsyncTaskLoader继承的自定义构建的加载器，我想在我的活动中使用它。他们每个都返回不同类型的结果。要将我的活动用于回调，我必须实现两个接口：

implements LoaderCallbacks<GetSyncListDataResult>, LoaderCallbacks<ErrorResult>

然而，尝试在同一个类中实现所需的方法，我最终得到了重复方法错误和擦除（???）错误：

// Methods for the first loader
public Loader<GetSyncListDataResult> onCreateLoader(int ID, Bundle bundle) ...
public void onLoaderReset(Loader<GetSyncListDataResult> loader) ...
public void onLoadFinished(Loader<GetSyncListDataResult> loader, GetSyncListDataResult result) ...

// Methods for the second loader
public Loader<ErrorResult> onCreateLoader(int ID, Bundle bundle) ...
public void onLoaderReset(Loader<ErrorResult> loader) ...
public void onLoadFinished(Loader<ErrorResult> loader, ErrorResult result) ...

显然，方法是冲突的，我需要一个简单的方法来解决这个问题。解决这个问题的正确方法是什么？

Answer 1

正确答案是根据@ dymmeh的评论，即不是Activity实现两个LoaderCallbacks接口，而是包含两个LoaderCallbacks的活动实现。举例来说：初始化您活动中的LoaderCallbacks字段...

private LoaderCallbacks<GetSyncListDataResult> dataResultLoaderListener
  = new LoaderCallbacks<GetSyncListDataResult>() { ...methods here... };

private LoaderCallbacks<ErrorResult> errorResultLoaderListener
  = new LoaderCallbacks<ErrorResult>() { ...methods here... };

...并声明你的装载机ID ......

private static final int DATA_RESULT_LOADER_ID = 1;
private static final int ERROR_RESULT_LOADER_ID = 2;

...然后初始化你的装载机......

getLoaderManager().initLoader(DATA_RESULT_LOADER_ID, dataResultBundle, dataResultLoaderListener);
getLoaderManager().initLoader(ERROR_RESULT_LOADER_ID, errorResultBundle, errorResultLoaderListener);

...完成！

Answer 2

class YourActivity extends AppCompatActivity implements LoaderManager.LoaderCallbacks {
// you still implements LoaderManager.LoaderCallbacks but without add <returnType> 
//and you have to cast the data into your needed data type in onLoadFinished()

    Private int loader1 = 1;
    private int loader2 =2;

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

    getSupportLoaderManager().initLoader(REVIEW_LOADER, null, this);
    getSupportLoaderManager().initLoader(REVIEW_LOADER, null, this);
}
    @Override
    public Loader onCreateLoader(int id, Bundle args) {
        if (id == loader1 ) {

            //YourLoaderClass1 is you loaderClass where you implement onStartLoading and loadingInBackground() 
            return new YourLoaderClass1();  
        } else if (id == loader2 ) {

            return new YourLoaderClass2();
        }
        return null;
    }

    @Override
    public void onLoadFinished(Loader loader, Object data) {
        int id = loader.getId();// find which loader you called
        if (id == loader1 ) {

            yourMethod1((List< >) data); // eg. cast data to List<String>
        } else if (id == loader2 ) {
            yourMethod1((String) data); // eg. cast data to String
        }
    }

    @Override
    public void onLoaderReset(Loader loader) {
        int id = loader.getId();
        if (id == loader1 ) {

        } else if (id == loader2 ) {

        }
    }
}

我的Github example

Answer 3

实际上，如果您在Activity类上实现LoaderManager.LoaderCallbacks<T>，并使用特定的加载程序ID来对结果进行操作，则更为简单。这样，您的代码更具可读性和功能性（因为内部加载程序回调的接口实现不再重复）。

例如：

    public class JobListActivity extends AppCompatActivity implements LoaderManager.LoaderCallbacks<NetworkResult> {

        public static final  int    SUBMIT_RISK_ASSESSMENT_LOADER = 546;
        public static final  int    LOAD_RISK_ASSESSMENT_LOADER   = 1546;

        public Loader<NetworkResult> onCreateLoader(int id, @Nullable Bundle args) {
            if (id == SUBMIT_RISK_ASSESSMENT_LOADER) {
                return new NetworkLoader( this, args.getString( NetworkLoader.URL_EXTRA ), NetworkLoader.POST, args.getString( BODY ), false ));
            } else if (id == LOAD_RISK_ASSESSMENT_LOADER) {
                return new NetworkLoader( this, args.getString( NetworkLoader.URL_EXTRA ), NetworkLoader.GET, null, false ) );
            }

            return null;
        }

        @Override
        public void onLoadFinished(@NonNull Loader<NetworkResult> loader, NetworkResult data) {
            if (data == null) {
                return;
            }

            Crashlytics.log( Log.INFO, TAG, "onLoadFinished with data [" + data + "]" );

            if (loader.getId() == SUBMIT_RISK_ASSESSMENT_LOADER) {
                    doSemethingElse(data);
            } else if (loader.getId() == LOAD_RISK_ASSESSMENT_LOADER) {
                    doSemethingElse(data);
            }
            LoaderManager.getInstance( this ).destroyLoader( loader.getId() );
    }

Answer 4

这不是必需的。实现LoaderManager.LoaderCallbacks。然后，每次初始化加载器时，给它一个唯一的ID。在回调中，您可以检测导致回调的加载程序的ID并采取适当的操作。

即

class MyLoader extends Activity implements LoaderManager.LoaderCallbacks<GetSyncDataResult> {
...
private static final int LOADER1 = 1;
private static final int LOADER2 = 2;
...
getLoaderManager().initLoader(LOADER1, null, this);
...
getLoaderManager().initLoader(LOADER2, null, this);
...

public Loader<GetSyncDataResult> onCreateLoader(int loaderId, Bundle args) {

    switch (loaderId) {

    case LOADER1: ...
    case LOADER2: ...
}
...

等等。

同一活动中的多个加载器

4 个答案: