Java在活动中执行代码之前等待线程（在另一个类中）完成

Question

In my android application I am trying to create a situation similar to ios delegate function.

(in ios->)where a class that perform the checking is called and after finish checking it will be redirected back using delegate to viewcontroller and perform next function.

Here is my Class

public class Checking{
    private boolean flag;

    public boolean getFlag(){
        return flag;
    }

    public void checkFunction(){
        //..... check database

        if(need to do call webservice){
            Thread thread = new Thread(){
                @Override
                public void run(){
                    // Perform webservice calling
                }
            };
            thread.start();
        }
        else{
            //end
        }
    }
}

---

Here is my Activity

public class ActivityA extends Activity{
    @Override
    public void onResume(){
        doChecking();
    }

    public void doChecking(){
        Checking check = new Checking();
        check.checkFunction();

        // should finish preform checking in Checking class before proceed
        if(check.getFlag()){
            // perform next function
        }
        else{
            // show alert
        }
    }
}

Problem with this is that right after calling the Checking class it straight away perform the if else below the function call. Which in some situation the check in Checking class have not finished and an empty alert is shown. The thread might or might not start depending on the database checking.

Can someone provide me a solution to overcome this? I know something is missing after calling the Checking class but I am not quite sure what to put it there in order to achieve the result.

Thanks in advance.

Answer 1

What you basically want to do is Hit a web service and then wait till you get the response of web service.

First thing, you don't need to create your own Thread t hit web service. Instead you can use AsyncTask

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.

Below is code of AsyncTask

class MyAsync extends AsyncTask<Void, Void, Void> {

    @Override
    protected Void doInBackground(Void... arg0) {
          //Hit your web service here
    }

    @Override
    protected void onPostExecute(final Void unused) {
          //Process the result here
    }

}

If you want to restrict user from accessing the app till web service is hit. You can show dialog from another method, like below:

class MyAsync extends AsyncTask<Void, Void, Void> {

    protected void onPreExecute() {
        loadingDialog.setMessage("Please wait...");
        loadingDialog.setCancelable(false);
        loadingDialog.show();
    }

    @Override
    protected Void doInBackground(Void... arg0) {
          //Hit your web service here
    }

    @Override
    protected void onPostExecute(final Void unused) {
        if (loadingDialog.isShowing()) {
            loadingDialog.dismiss();
        } 
        //Process the result here
    }

}

Answer 2

It can be implemented in the following way, by passing the activity in the Checking class's construtor and using it to call showAlert() function in the ActivityA class.

public class Checking{
 Activity activity_;

public Checking(Activity activity){
   this.activity_ = activity;
}

private boolean flag;

public boolean getFlag(){
    return flag;
}

public void checkFunction(){
    //..... check database

    if(need to do call webservice){
        Thread thread = new Thread(){
            @Override
            public void run(){
                // Perform webservice calling
                //after all the process
                 Handler handler = new Handler();
                 handler.post(new Runnable{
                  @Override
                  public void run(){
                    (MyActivity) activity_.showAlert();
                  }});
            }
        };
        thread.start();
    }
    else{
        //end
    }
}
}

public class ActivityA extends Activity{
@Override
public void onResume(){
    doChecking();
}

public void doChecking(){
    Checking check = new Checking(ActivityA.this);
    check.checkFunction();
}

public void showAlert(){
      // should finish preform checking in Checking class before proceed
   if(check.getFlag()){
        // perform next function
   }else{
          // show alert
   }
}
}