开发笔记：数据加载

开发pad应用时，通常使用v4的Fragment，使用v4包本身的LoaderManager：

使用v4中的LoaderManager的步骤如下

1.新建Fragment时要实现接口LoaderCallbacks

android.support.v4.app.LoaderManager.LoaderCallbacks<Cursor>

2.在onCreate方法中调用initLoader方法

<Cursor> Loader<Cursor> android.support.v4.app.LoaderManager.initLoader(int arg0, Bundle arg1, LoaderCallbacks<Cursor> arg2)

3.实现接口LoaderCallbacks的抽象方法

public Loader<Cursor> onCreateLoader(int arg0, Bundle arg1);
public void onLoadFinished(Loader<Cursor> arg0, Cursor arg1);
public void onLoaderReset(Loader<Cursor> arg0);

新建TvieRequest类，封装了从网络获取数据大部分细节，提供从网络获取数据大部分功能。

TvieRequest类分以下几个部分：

1. 定义变量

private String requestUrl;
private Map<String, String> paramValues;
private ICallback callback;
private NetUtil.HttpMethod httpMethod;
private Class<?> resultType;
private int requestCode;
private int resultCode;

2. 定义常量

public static final int RESULT_SUCCESS = 1;
public static final int RESULT_ERROR = 2;
public static final int RESULT_EMPTY = 3;
public static final int RESULT_CANCEL = 4;

3. 定义接口

public static interface ICallback {
    public void onRequestFinished(int requestCode, int resultCode, IVideoResult result);
    public void onRequestStarted(int requestCode);
};

4. 定义异步任务类

private class MyAsyncTask extends AsyncTask<Void, Void, IVideoResult> {
    @Override
    protected void onPreExecute() {
        callback.onRequestStarted(requestCode);
    }
    @Override
    protected void onPostExecute(IVideoResult result) {
        callback.onRequestFinished(requestCode, resultCode, result);
    }
    private String cache(String data) {
        File cacheFile = CacheUtils.getCacheFile(requestUrl, paramValues);
        if (data == null) {
            data = CacheUtils.getDataFromCache(cacheFile);
        } else {
            CacheUtils.updateCache(cacheFile, data);
        }
        return data;
    }
    @Override
    protected IVideoResult doInVoid...  params) {
        IVideoResult result = null;
        String response = null;
        JSONObject object = null;
        response = NetUtil.request(paramValues, requestUrl, httpMethod);
        if (httpMethod == NetUtil.HttpMethod.GET) {
            response = cache(response);
        }
        if (response == null) {
            resultCode = RESULT_ERROR;
            return null;
        } else if (response.length() == 0) {
            resultCode = RESULT_EMPTY;
            return null;
        }
        object = JSONObject.parse(response);
        result = (IVideoResult) ReflectUtils.getNewInstance(resultType.getName());
        result.parseJson(object);
                                                               
        if(result != null && result.isSuccess())
            resultCode = RESULT_SUCCESS;
        else
            resultCode = RESULT_ERROR;
        return result;
    }
}

5. 定义构造方法，创建TvieRequest实例

public TvieRequest(String requestUrl, Map<String, String> paramValues, ICallback callback, HttpMethod httpMethod,
        Class<?> resultType, int requestCode) {
    this.requestUrl = requestUrl;
    this.paramValues = paramValues;
    this.callback = callback;
    this.httpMethod = httpMethod;
    this.resultType = resultType;
    this.requestCode = requestCode;
}

6. 定义execute方法，调用MyAsyncTask的execute方法

private void execute() {
    new MyAsyncTask().execute();
}

7. 定义三个静态方法

public static void post(int requestCode, Class<?> resultType, ICallback callback, String requestUrl,
        Map<String, String> params) {
    new TvieRequest(requestUrl, params, callback, NetUtil.HttpMethod.POST, resultType, requestCode).execute();
}
public static void get(int requestCode, Class<?> resultType, ICallback callback, String requestUrl,
        Map<String, String> params) {
    new TvieRequest(requestUrl, params, callback, NetUtil.HttpMethod.GET, resultType, requestCode).execute();
}
public static void delete(int requestCode, Class<?> resultType, ICallback callback, String requestUrl,
        Map<String, String> params) {
    new TvieRequest(requestUrl, params, callback, NetUtil.HttpMethod.DELETE, resultType, requestCode).execute();
}