取消 AsyncTask

在下面的示例中，如果有人在任務執行時按某個主頁按鈕，則該任務將被取消。在這個特定的取消中它應該在執行時中斷。

 public class MainActivity extends AppCompatActivity {
    
    private static AtomicBoolean inWork;
    private CustomAsyncTask asyncTask;
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
        inWork = new AtomicBoolean(false);
        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
    
                executeAsyncTaskOperation();
            }
        });
    }
    
    
    private void executeAsyncTaskOperation() {
        Boolean[] bools = new Boolean[10];
        for (int k = 0; k < 10; k++) {
            if (k % 2 == 0) {
                bools[k] = true;
            } else {
                bools[k] = false;
            }
        }
        asyncTask = new CustomAsyncTask(this);
        asyncTask.execute(bools);
    }
    
    //pressing the home button while the task is running will trigger the onStop being called.
    @Override
    protected void onStop() {
        if (asyncTask.getStatus() == AsyncTask.Status.RUNNING) {
            asyncTask.cancel(true);
        }
        super.onStop();
    }
    
    private static class CustomAsyncTask extends AsyncTask<Boolean, Void, Integer> {
    
        private Context context;
        private ProgressDialog progressDialog;
    
        public CustomAsyncTask(Context context) {
            this.context = context;
        }
    
        @Override
        protected void onCancelled() {
            inWork.set(false);
            if (progressDialog != null && progressDialog.isShowing()) {
                progressDialog.dismiss();
                Log.d(CustomAsyncTask.class.getCanonicalName(), "progressdialog is dismissed.");
            }
        }
    
        @Override
        protected void onPreExecute() {
            progressDialog = ProgressDialog.show(context, "Please wait...", "Loading data from web");
        }
    
        @Override
        protected Integer doInBackground(Boolean... params) {
            int count = 0;
            inWork.set(true);
            try {
                Thread.sleep(1000);
                Log.d(CustomAsyncTask.class.getCanonicalName(), "doInBackground");
                if (!isCancelled()) {
                    for (Boolean param : params) {
                        if (param) {
    
                            count++;
                        }
                    }
                } else {
                    Log.d(CustomAsyncTask.class.getCanonicalName(), "doInBackground is cancelled.");
                }
    
            } catch (Exception exc) {
                Log.e(CustomAsyncTask.class.getCanonicalName(), "exception");
                count = 0;
            }
            return count;
        }
    
        @Override
        protected void onPostExecute(Integer s) {
            if (!isCancelled()) {
                inWork.set(false);
                if (progressDialog != null && progressDialog.isShowing()) {
                    progressDialog.dismiss();
                }
                if (s != null && s > 0) {
                    Toast.makeText(context, "finished loading: " + s + " tasks", Toast.LENGTH_LONG).show();
                } else {
                    Toast.makeText(context, "finished unsuccessfully!", Toast.LENGTH_LONG).show();
    
                }
            } else {
                Log.d(CustomAsyncTask.class.getCanonicalName(), "onPostExecute is cancelled.");
            }
        }
    }
}