从位于异步任务doInBackGround中的回调返回一个值

Question

I have the following bit of code:

here is a link to the doucmentation fo rthe asyncHttp: Link

This is what calls the login task:

mAuthTask = new UserLoginTask();
mAuthTask.execute((Void) null);

Here is the async Task provided by android template activity:

    public class UserLoginTask extends AsyncTask<Void, Void, Boolean> {
    @Override
    protected Boolean doInBackground(Void... params) {
        // TODO: attempt authentication against a network service.

        Network.login(mEmail, mPassword, new AsyncHttpResponseHandler() {

            @Override
            public void onSuccess(int statusCode, Header[] headers,
                    byte[] responseBody) {

                if (statusCode == 200) {
                    // Successfully got a response
                    for (int i = 0; i < headers.length; i++) {
                        if (headers[i].getName().equalsIgnoreCase("token")) {
                            // Set the token to the received value
                            Network.SetToken(headers[i].getValue());
                    // >>>>>>>      return true;   <<<<<<<<<
                        }
                    }
                }
                // >>>>> return false  <<<<<<<<<<<<

            }

            @Override
            public void onFailure(int statusCode, Header[] headers,
                    byte[] responseBody, Throwable error) {
                // Response failed :(
                  //     >>>>>>>>>>>>>>>>>> return false <<<<<<<<<<<<<
            }           
        });

        // TODO: register the new account here.
        return true;
    }

    @Override
    protected void onPostExecute(final Boolean success) {
        mAuthTask = null;
        showProgress(false);

        if (success) {
            finish();
        } else {
            mPasswordView
                    .setError(getString(R.string.error_incorrect_password));
            mPasswordView.requestFocus();
        }
    }

How can I return true or false from within my AsyncHttpResponseHandler and then return that value to the async task? So that it can then successfully execute its on post method.

I can only think of settings variable and then blocking on it. But then that defeatists the point of it being async and I would rather stay away from that.

Answer 1

From the developer documents

AsyncTask enables proper and easy use of the UI thread. This class allows to perform background operations and publish results on the UI thread without having to manipulate threads and/or handlers.AsyncTask is designed to be a helper class around Thread and Handler and does not constitute a generic threading framework. AsyncTasks should ideally be used for short operations (a few seconds at the most.)

Now that said if you really want to finish in onPostExecute you can do this

public class UserLoginTask extends AsyncTask<Void, Void, Boolean> {
    @Override
    protected Boolean doInBackground(Void... params) {
        // TODO: attempt authentication against a network service.

        final ResponseContainer responseContainer = new ResponseContainer();
        Network.login(mEmail, mPassword, new AsyncHttpResponseHandler() {

            @Override
            public void onSuccess(int statusCode, Header[] headers,
                    byte[] responseBody) {

                if (statusCode == 200) {
                    // Successfully got a response
                    for (int i = 0; i < headers.length; i++) {
                        if (headers[i].getName().equalsIgnoreCase("token")) {
                            // Set the token to the received value
                            Network.SetToken(headers[i].getValue());
                    // >>>>>>>      return true;   <<<<<<<<<
                            responseContainer.result = true;
                        }
                    }
                }
                // >>>>> return false  <<<<<<<<<<<<
                responseContainer.result = false;
            }

            @Override
            public void onFailure(int statusCode, Header[] headers,
                    byte[] responseBody, Throwable error) {
                // Response failed :(
                  //     >>>>>>>>>>>>>>>>>> return false <<<<<<<<<<<<<
                responseContainer.result = false;
            }           
        });

        // TODO: register the new account here.
        return responseContainer.result;
    }

    @Override
    protected void onPostExecute(final Boolean success) {
        mAuthTask = null;
        showProgress(false);

        if (success) {
            finish();
        } else {
            mPasswordView
                    .setError(getString(R.string.error_incorrect_password));
            mPasswordView.requestFocus();
        }
    }

    private class ResponseContainer {
        public boolean result;
    }
}

Answer 2

If, and only if, the Network call runs on it's own thread, you could try to do this by blocking doInBackground by figuring out which thread the network call uses and using Thread.join .

However, I don't think you can guarantee it will, since you have not specified the executor and that can change outside the code you've given. So, if I had this issue, I would turn the code around and use an AsyncHandler to respond to the response of the Network call, avoiding nested async operations altogether. Something like this:

public void loginUser() {
    Network.login(mEmail, mPassword, new AsyncHttpResponseHandler() {

        @Override
        public void onSuccess(int statusCode, Header[] headers,
                byte[] responseBody) {

            if (statusCode == 200) {
                // Successfully got a response
                for (int i = 0; i < headers.length; i++) {
                    if (headers[i].getName().equalsIgnoreCase("token")) {
                        // Set the token to the received value
                        Network.SetToken(headers[i].getValue());
                        new RegisterUserTask(statusCode, responseBody).execute();
                    }
                }
            }
            // respond to a failed authentication.
            mPasswordView
                .setError(getString(R.string.error_incorrect_password));
            mPasswordView.requestFocus();

        }

        @Override
        public void onFailure(int statusCode, Header[] headers,
                byte[] responseBody, Throwable error) {
            // Response failed :(
              // Show some sort of error.
        }           
    });
}

public class RegisterUserTask extends AsyncTask<Void, Void, Boolean> {
    private int statusCode;
    private byte[] body;

    public RegisterUserTask(int statusCode, byte[] body) {
        this.statusCode = statusCode;
        this.body = body;
    }

    @Override
    protected Boolean doInBackground(Void... params) {
        // TODO: register the new account here.

        return true;
    }

    @Override
    protected void onPostExecute(final Boolean success) {
        mAuthTask = null;
        showProgress(false);

        if (success) {
            finish();
        }
    }
}

Answer 3

Isn't the Network.login already async?

You can use Handler system :

private static final int SUCCESS= 0;
private static final int FAIL= 1;
//In your class
    private final Handler handler = new Handler() {

        @Override
        public void handleMessage(final Message msg) {
            runOnUiThread(new Runnable() {

                @Override
                public void run() {
                    switch (msg.what) {
                        case SUCCESS:
                            finish();
                            break;
                        case FAIL:
                            mPasswordView.setError(getString(R.string.error_incorrect_password));
                            mPasswordView.requestFocus();
                            break;
                        default:
                            break;
                    }
                }
            });
        }
    };

    public class UserLoginTask extends AsyncTask<Void, Void, Boolean> {
        @Override
        protected Boolean doInBackground(Void... params) {
            // TODO: attempt authentication against a network service.

            Network.login(mEmail, mPassword, new AsyncHttpResponseHandler() {

                @Override
                public void onSuccess(int statusCode, Header[] headers,
                        byte[] responseBody) {

                    if (statusCode == 200) {
                        // Successfully got a response
                        for (int i = 0; i < headers.length; i++) {
                            if (headers[i].getName().equalsIgnoreCase("token")) {
                                // Set the token to the received value
                                Network.SetToken(headers[i].getValue());
                                handler.sendEmptyMessage(SUCCESS);
                            }
                        }
                    }
                    // >>>>> return false  <<<<<<<<<<<<
                    handler.sendEmptyMessage(FAIL);
                }

                @Override
                public void onFailure(int statusCode, Header[] headers,
                        byte[] responseBody, Throwable error) {
                    // Response failed :(
                    handler.sendEmptyMessage(FAIL);
                      //     >>>>>>>>>>>>>>>>>> return false <<<<<<<<<<<<<
                }           
            });

            // TODO: register the new account here.
            return true;
        }

        @Override
        protected void onPostExecute(final Boolean success) {

        }
    }

But I think you don't have to use the asyncTask with Network.login.. If it's synchrone maybe just a new Thread ?

new Thread() {
                @Override
                public void run() {
                    Network.login(...) {
                       ...
                    }
                };
 }.start();

Answer 4

If I get your point you mean finding a way to handle an event like AsyncTaskCompleted and do your staff there. The solution is defining an interface like WebServiceCallbackProxy:

public interface WebServiceCallbackProxy {

    void CallBack(char[] jsonData, String serviceName, boolean isCommunicationSucceed, HttpRequestType reguestType, String serviceTicket);
}

Then define an instance in your AsyncTask:

public class AsynServiceCall extends AsyncTask<String, Integer, char[]> {

WebServiceCallbackProxy proxy;
.... 
public AsynServiceCall(WebServiceCallbackProxy webServiceProxy, ProgressDialog progressDialog) {
    this.proxy = webServiceProxy;

}

Then call your CallBackMethod on PostExecute:

protected void onPostExecute(char[] response) {
        if (this.progressDialog != null) {
            progressDialog.dismiss();
        }
        if(proxy != null)
            proxy.CallBack(response, this.serviceName, this.isCommunicationSucced, this.requestType, this.serivceTicket);
    }

Doing so, you have an AsyncTask that has OnCompleted CallBack Method.