我有两门课。我的主活动和一个扩展AsyncTask，现在在我的主活动中，我需要从AsyncTask中的OnPostExecute()获得结果。如何将结果传递给我的主活动?
下面是示例代码。
我的主要活动。
public class MainActivity extends Activity{
AasyncTask asyncTask = new AasyncTask();
@Override
public void onCreate(Bundle aBundle) {
super.onCreate(aBundle);
//Calling the AsyncTask class to start to execute.
asyncTask.execute(a.targetServer);
//Creating a TextView.
TextView displayUI = asyncTask.dataDisplay;
displayUI = new TextView(this);
this.setContentView(tTextView);
}
}
这是AsyncTask类
public class AasyncTask extends AsyncTask<String, Void, String> {
TextView dataDisplay; //store the data
String soapAction = "http://sample.com"; //SOAPAction header line.
String targetServer = "https://sampletargeturl.com"; //Target Server.
//SOAP Request.
String soapRequest = "<sample XML request>";
@Override
protected String doInBackground(String... string) {
String responseStorage = null; //storage of the response
try {
//Uses URL and HttpURLConnection for server connection.
URL targetURL = new URL(targetServer);
HttpURLConnection httpCon = (HttpURLConnection) targetURL.openConnection();
httpCon.setDoOutput(true);
httpCon.setDoInput(true);
httpCon.setUseCaches(false);
httpCon.setChunkedStreamingMode(0);
//properties of SOAPAction header
httpCon.addRequestProperty("SOAPAction", soapAction);
httpCon.addRequestProperty("Content-Type", "text/xml; charset=utf-8");
httpCon.addRequestProperty("Content-Length", "" + soapRequest.length());
httpCon.setRequestMethod(HttpPost.METHOD_NAME);
//sending request to the server.
OutputStream outputStream = httpCon.getOutputStream();
Writer writer = new OutputStreamWriter(outputStream);
writer.write(soapRequest);
writer.flush();
writer.close();
//getting the response from the server
InputStream inputStream = httpCon.getInputStream();
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
ByteArrayBuffer byteArrayBuffer = new ByteArrayBuffer(50);
int intResponse = httpCon.getResponseCode();
while ((intResponse = bufferedReader.read()) != -1) {
byteArrayBuffer.append(intResponse);
}
responseStorage = new String(byteArrayBuffer.toByteArray());
} catch (Exception aException) {
responseStorage = aException.getMessage();
}
return responseStorage;
}
protected void onPostExecute(String result) {
aTextView.setText(result);
}
}
可能有点过分了，但我为执行代码和结果都提供了回调。显然，为了线程安全，你要小心你在执行回调中访问的内容。
AsyncTask实现:
public class AsyncDbCall<ExecuteType,ResultType> extends AsyncTask<ExecuteType, Void,
ResultType>
{
public interface ExecuteCallback<E, R>
{
public R execute(E executeInput);
}
public interface PostExecuteCallback<R>
{
public void finish(R result);
}
private PostExecuteCallback<ResultType> _resultCallback = null;
private ExecuteCallback<ExecuteType,ResultType> _executeCallback = null;
AsyncDbCall(ExecuteCallback<ExecuteType,ResultType> executeCallback, PostExecuteCallback<ResultType> postExecuteCallback)
{
_resultCallback = postExecuteCallback;
_executeCallback = executeCallback;
}
AsyncDbCall(ExecuteCallback<ExecuteType,ResultType> executeCallback)
{
_executeCallback = executeCallback;
}
@Override
protected ResultType doInBackground(final ExecuteType... params)
{
return _executeCallback.execute(params[0]);
}
@Override
protected void onPostExecute(ResultType result)
{
if(_resultCallback != null)
_resultCallback.finish(result);
}
}
一个回调:
AsyncDbCall.ExecuteCallback<Device, Device> updateDeviceCallback = new
AsyncDbCall.ExecuteCallback<Device, Device>()
{
@Override
public Device execute(Device device)
{
deviceDao.updateDevice(device);
return device;
}
};
最后执行异步任务:
new AsyncDbCall<>(addDeviceCallback, resultCallback).execute(device);
我通过使用线程和处理程序/消息使它工作。
步骤如下:
声明进度对话框
ProgressDialog loadingdialog;
创建一个函数，在操作结束时关闭对话框。
private Handler handler = new Handler() {
@Override
public void handleMessage(Message msg) {
loadingdialog.dismiss();
}
};
编码你的执行细节:
public void startUpload(String filepath) {
loadingdialog = ProgressDialog.show(MainActivity.this, "Uploading", "Uploading Please Wait", true);
final String _path = filepath;
new Thread() {
public void run() {
try {
UploadFile(_path, getHostName(), getPortNo());
handler.sendEmptyMessage(0);
} catch (Exception e) {
Log.e("threadmessage", e.getMessage());
}
}
}.start();
}
您可以编写自己的侦听器。它和HelmiB的答案一样，但看起来更自然:
创建监听器接口:
public interface myAsyncTaskCompletedListener {
void onMyAsynTaskCompleted(int responseCode, String result);
}
然后写你的异步任务:
public class myAsyncTask extends AsyncTask<String, Void, String> {
private myAsyncTaskCompletedListener listener;
private int responseCode = 0;
public myAsyncTask() {
}
public myAsyncTask(myAsyncTaskCompletedListener listener, int responseCode) {
this.listener = listener;
this.responseCode = responseCode;
}
@Override
protected void onPreExecute() {
super.onPreExecute();
}
@Override
protected String doInBackground(String... params) {
String result;
String param = (params.length == 0) ? null : params[0];
if (param != null) {
// Do some background jobs, like httprequest...
return result;
}
return null;
}
@Override
protected void onPostExecute(String finalResult) {
super.onPostExecute(finalResult);
if (!isCancelled()) {
if (listener != null) {
listener.onMyAsynTaskCompleted(responseCode, finalResult);
}
}
}
}
最后在activity中实现监听器:
public class MainActivity extends AppCompatActivity implements myAsyncTaskCompletedListener {
@Override
public void onMyAsynTaskCompleted(int responseCode, String result) {
switch (responseCode) {
case TASK_CODE_ONE:
// Do something for CODE_ONE
break;
case TASK_CODE_TWO:
// Do something for CODE_TWO
break;
default:
// Show some error code
}
}
这是你如何调用asyncTask:
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Some other codes...
new myAsyncTask(this,TASK_CODE_ONE).execute("Data for background job");
// And some another codes...
}
试试这个:
public class SomAsyncTask extends AsyncTask<String, Integer, JSONObject> {
private CallBack callBack;
public interface CallBack {
void async( JSONObject jsonResult );
void sync( JSONObject jsonResult );
void progress( Integer... status );
void cancel();
}
public SomAsyncTask(CallBack callBack) {
this.callBack = callBack;
}
@Override
protected JSONObject doInBackground(String... strings) {
JSONObject dataJson = null;
//TODO query, get some dataJson
if(this.callBack != null)
this.callBack.async( dataJson );// asynchronize with MAIN LOOP THREAD
return dataJson;
}
@Override
protected void onProgressUpdate(Integer... values) {
super.onProgressUpdate(values);
if(this.callBack != null)
this.callBack.progress(values);// synchronize with MAIN LOOP THREAD
}
@Override
protected void onPostExecute(JSONObject jsonObject) {
super.onPostExecute(jsonObject);
if(this.callBack != null)
this.callBack.sync(jsonObject);// synchronize with MAIN LOOP THREAD
}
@Override
protected void onCancelled() {
super.onCancelled();
if(this.callBack != null)
this.callBack.cancel();
}
}
用法示例:
public void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
final Context _localContext = getContext();
SomeAsyncTask.CallBack someCallBack = new SomeAsyncTask.CallBack() {
@Override
public void async(JSONObject jsonResult) {//async thread
//some async process, e.g. send data to server...
}
@Override
public void sync(JSONObject jsonResult) {//sync thread
//get result...
//get some resource of Activity variable...
Resources resources = _localContext.getResources();
}
@Override
public void progress(Integer... status) {//sync thread
//e.g. change status progress bar...
}
@Override
public void cancel() {
}
};
new SomeAsyncTask( someCallBack )
.execute("someParams0", "someParams1", "someParams2");
}
