Question

我试图重构我的代码并将我的代码从Async Task移动到加载器。我通过Android Performance视频系列this了解了加载器的好处我知道为什么使用装载机以及它有什么类和东西（理论）。但是我无法掌握工作概念，因此编写了这个糟糕的代码。因此我也无法调试它。 **编辑：我能够使它工作，但我仍然认为我以错误的方式调用它。

new EarthquakeAsyncTaskLoader（this）.forceLoad（）;

如果有人可以帮助我，请......... **

import android.content.AsyncTaskLoader;
import android.content.Context;
import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.support.v4.app.LoaderManager;
import android.support.v4.content.Loader;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ListView;

import java.io.IOException;
import java.util.ArrayList;

public class EarthQuakeActivity extends AppCompatActivity implements LoaderManager.LoaderCallbacks<ArrayList<EarthQuakes>> {

ArrayList<EarthQuakes> earthquakes = null;


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

    getSupportLoaderManager().initLoader(1, null, this);

}// End of onCreate

@Override
public Loader<ArrayList<EarthQuakes>> onCreateLoader(int id, Bundle args) {

    **new EarthquakeAsyncTaskLoader(this).forceLoad();**
}

@Override
public void onLoadFinished(Loader<ArrayList<EarthQuakes>> loader, ArrayList<EarthQuakes> data) {
}

@Override
public void onLoaderReset(Loader<ArrayList<EarthQuakes>> loader) {

}


public class EarthquakeAsyncTaskLoader extends AsyncTaskLoader<ArrayList<EarthQuakes>> {

    public EarthquakeAsyncTaskLoader(Context context) {
        super(context);
    }


    @Override
    protected void onStartLoading() {
        // If the data is there, don't start again
        if (earthquakes != null) {
            deliverResult(earthquakes);
        } else {
            //Start the loader
            forceLoad();
        }
    }

    @Override
    public ArrayList<EarthQuakes> loadInBackground() {
        // Get the populated list from QueryUtils java class
        try {
           // Here in QueryUtils, I am making an HTTP network call
           // Thus it has to be done in a helper background thread
            earthquakes = QueryUtils.getArrayList();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return earthquakes;
    }


    @Override
    public void deliverResult(ArrayList<EarthQuakes> data) {

        // Feed the adapter with data and display it
        ListView earthquakesList = (ListView) findViewById(R.id.listV);
        final EarthQuakeAdapter adapter = new EarthQuakeAdapter(getApplicationContext(), data);
        earthquakesList.setAdapter(adapter);

        earthquakesList.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
                EarthQuakes currentEarthquake = adapter.getItem(i);
                Uri earthquakeUri = Uri.parse(currentEarthquake.getUrl());

        // Create a new intent to view the earthquake URI
                Intent websiteIntent = new Intent(Intent.ACTION_VIEW, earthquakeUri);

        // Send the intent to launch a new activity
                startActivity(websiteIntent);
            }
        });

    }
}//End of Async Task Loader


//EarthQuakes is my class. I don't think you'll need this. But anyway:
public class EarthQuakes {


    private double mMagnitude;
    private String mLocationSmallText;
    private String mLocationMainText;
    private String mDateOfEarthquake;
    private String mUrl;


    // Default Constructor
    public EarthQuakes(Double mag, String locationSmallText, String locationMainCityName, String dateE, String Url) {
        this.mMagnitude = mag;
        this.mLocationSmallText = locationSmallText;
        this.mLocationMainText = locationMainCityName;
        this.mDateOfEarthquake = dateE;
        this.mUrl = Url;
    }


    // Public getters
    public Double getMagnitude() {
        return mMagnitude;
    }

    public String getLocationSmallTextEarthquake() {
        return mLocationSmallText;
    }

    public String getLocationLargeTextEarthquake() {
        return mLocationMainText;
    }

    public String getDateOfEarthquake() {
        return mDateOfEarthquake;
    }

    public String getUrl() {
        return mUrl;
    }

}

Answer 1

此替代方案也有效：

getSupportLoaderManager().initLoader(1, null, this).forceload();

但是，这只是提及here加载器问题的一种方法。如果您使用的AsyncTaskLoader不是CursorLoader，则会出现此问题。您需要实现onStartLoading()并在那里处理调用forceLoad()。强烈建议您浏览问题页面。

如果您在整个应用中使用多个加载器，并且不希望每次都实现onStartLoading()。这是一个自定义加载器类，您可以将其包含在您的应用中，并从此继承，而不是通常的AsyncTaskLoader：

WrappedAsyncTaskLoader.java（原作者：Alexander Blom）

public abstract class WrappedAsyncTaskLoader<D> extends AsyncTaskLoader<D> {

private D mData;

/**
 * Constructor of <code>WrappedAsyncTaskLoader</code>
 *
 * @param context The {@link Context} to use.
 */
public WrappedAsyncTaskLoader(Context context) {
    super(context);
}

/**
 * {@inheritDoc}
 */
@Override
public void deliverResult(D data) {
    if (!isReset()) {
        this.mData = data;
        super.deliverResult(data);
    } else {
        // An asynchronous query came in while the loader is stopped
    }
}

/**
 * {@inheritDoc}
 */
@Override
protected void onStartLoading() {
    super.onStartLoading();
    if (this.mData != null) {
        deliverResult(this.mData);
    } else if (takeContentChanged() || this.mData == null) {
        forceLoad();
    }
}

/**
 * {@inheritDoc}
 */
@Override
protected void onStopLoading() {
    super.onStopLoading();
    // Attempt to cancel the current load task if possible
    cancelLoad();
}

/**
 * {@inheritDoc}
 */
@Override
protected void onReset() {
    super.onReset();
    // Ensure the loader is stopped
    onStopLoading();
    this.mData = null;
}
}

在android中使用Loaders的简单代码出错

1 个答案: