java - 如何让 onStart() 方法等到 onCreate() 方法完成

Question

我有一个 AsyncTask 从 Activity 的 onCreate() 方法运行，该方法从 mysql 数据库获取列表。
在 onStart() 方法中，我调用这些方法来启动一些动画。

我希望这些动画仅在获取列表后才启动。
即:AsyncTask 完成后。

我知道我可以在 AsyncTask 对象的 onPostExecute() 方法中启动动画。
但我希望每次 Activity 可见时都启动这些动画。

应该是这样的:

FirstActivity(ListFetches 和动画启动)。
SecondActivity 到 FirstActivity(动画开始，列表已获取)。

下面是我的代码

public class FirstSelection extends ActionBarActivity {
    Activity context;
    HttpPost httppost;
    StringBuffer buffer;
    HttpResponse response;
    HttpClient httpclient;
    ProgressDialog pd;
    CustomAdapter adapter;
    ListView listProduct;
    ArrayList<String> records;
    Intent i;
    Intent j;
    Intent k;
    double version;
    double oldVer = 1.0;
    String downloadlink;
    DownloadManager dm;
    private long enqueue;
    private Toolbar toolbar;
    ValueAnimator colorAnimation;
    FrameLayout myframe;
    ValueAnimator statusAnim;
    String[] menu;
    DrawerLayout dLayout;
    ListView dList;
    ArrayAdapter<String> dadapter;
    ImageView image;
    Animation anim;


    protected void onCreate(Bundle savedInstanceState) {
   //TODO Auto-generated method stub
   super.onCreate(savedInstanceState);
   setContentView(R.layout.first_selection);
   toolbar = (Toolbar) findViewById(R.id.new_tool);
   myframe = (FrameLayout)findViewById(R.id.myframe);
   menu = new String[]{"Refresh","Report Broken Link","Request songs"};
   dLayout = (DrawerLayout)findViewById(R.id.drawer_layout);
   dList = (ListView)findViewById(R.id.navList);
   image = (ImageView)findViewById(R.id.loader);
   anim = AnimationUtils.loadAnimation(this, R.anim.myanim);
   image.startAnimation(anim);
   dadapter = new ArrayAdapter<String>(this,R.layout.drawer_list_item,menu);
   dList.setAdapter(dadapter);
    setSupportActionBar(toolbar);
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT) {
       Window w = getWindow(); // in Activity's onCreate() for instance
       w.setFlags(WindowManager.LayoutParams.FLAG_TRANSLUCENT_NAVIGATION, WindowManager.LayoutParams.FLAG_TRANSLUCENT_NAVIGATION);
       w.setFlags(WindowManager.LayoutParams.FLAG_TRANSLUCENT_STATUS, WindowManager.LayoutParams.FLAG_TRANSLUCENT_STATUS);
   }
   context=this;
   records=new ArrayList<String>();
   listProduct=(ListView)findViewById(R.id.product_list);
   i = new Intent(this, ReportActivity.class);
   j = new Intent(this, RequestActivity.class);
   k = new Intent(this, AboutDeveloper.class);
   BackTask bt=new BackTask();
   bt.execute();
   adapter=new CustomAdapter(context, R.layout.list_item_first,R.id.pro_name, records);
   listProduct.setAdapter(adapter);
   listProduct.setOnItemClickListener(new OnItemClickListener(){
       @Override
       public void onItemClick(AdapterView<?> arg0, View v, int position, long id){

           Intent songIntent = new Intent(getApplicationContext(), SecondSelection.class);
           startActivity(songIntent);

       }

   });

 //Animation for Action Bar

   Integer colorFrom = getResources().getColor(R.color.first);
   Integer colorTo = getResources().getColor(R.color.last);
   colorAnimation = ValueAnimator.ofObject(new ArgbEvaluator(), colorFrom, colorTo);
   colorAnimation.addUpdateListener(new AnimatorUpdateListener() {

       @Override
       public void onAnimationUpdate(ValueAnimator animator) {
           toolbar.setBackgroundColor((Integer)animator.getAnimatedValue());
       }

   });


   //Animation for Status Bar

   Integer colorFirst = getResources().getColor(R.color.begin);
   Integer colorLast = getResources().getColor(R.color.end);
   statusAnim = ValueAnimator.ofObject(new ArgbEvaluator(), colorFirst, colorLast);
   statusAnim.addUpdateListener(new AnimatorUpdateListener() {

       @Override
       public void onAnimationUpdate(ValueAnimator animator) {
           myframe.setBackgroundColor((Integer)animator.getAnimatedValue());
       }

   });

   //Start the Animations after fetching the list.
   //After executing the bt.execute()

   }

    @Override
    public void onBackPressed() {
        if (dLayout.isDrawerOpen(dList)) {
           dLayout.closeDrawer(dList);
        } 

        else{
            doExit();
        }
    }


    /*@Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {

        if (keyCode == KeyEvent.KEYCODE_BACK) {

            doExit();
        }

        return super.onKeyDown(keyCode, event);
    }**/

    private void doExit() {

        AlertDialog.Builder alertDialog = new AlertDialog.Builder(
                FirstSelection.this);

        alertDialog.setPositiveButton("Yes", new OnClickListener() {

            @Override
            public void onClick(DialogInterface dialog, int which) {
                finish();
            }
        });

        alertDialog.setNegativeButton("No", null);

        alertDialog.setMessage("Do you want to exit?");
        alertDialog.setTitle("something");
        alertDialog.show();
    }

    @Override
    public void onStart() {
        super.onStart();
        //These are my animations
        statusAnim.setDuration(800);
        colorAnimation.setDuration(1300);
        colorAnimation.start();
        statusAnim.start();

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        return super.onOptionsItemSelected(item);
    }

    // background process to make a request to server and list product
    // information
    private class BackTask extends AsyncTask<Void, Void, Void> {
        protected void onPreExecute() {
            super.onPreExecute();
        //  pd = new ProgressDialog(context);
        //  pd.setTitle("Retrieving data");
        //  pd.setMessage("Please wait.");
        //  pd.setCancelable(true);
        //  pd.setIndeterminate(true);
        //  pd.show();

        }

        protected Void doInBackground(Void... params) {

            InputStream is = null;
            String result = "";
            try {

                records.clear();
                httpclient = new DefaultHttpClient();
                httppost = new HttpPost(
                        "somelink");
                response = httpclient.execute(httppost);
                HttpEntity entity = response.getEntity();
                is = entity.getContent();

            } catch (Exception e) {

                if (pd != null)
                    pd.dismiss(); // close the dialog if error occurs
                Log.e("ERROR", e.getMessage());

            }

            // convert response to string
            try {
                BufferedReader reader = new BufferedReader(
                        new InputStreamReader(is, "utf-8"), 8);
                StringBuilder sb = new StringBuilder();
                String line = null;
                while ((line = reader.readLine()) != null) {
                    sb.append(line + "\n");
                }
                is.close();
                result = sb.toString();
            } catch (Exception e) {
                Log.e("ERROR", "Error converting result " + e.toString());

            }

            // parse json data
            try {

                JSONArray jArray = new JSONArray(result);
                for (int i = 0; i < jArray.length(); i++) {
                    JSONObject json_data = jArray.getJSONObject(i);
                    String record = json_data.getString("context") + "__"
                            + json_data.getDouble("version");
                    version = json_data.getDouble("version");
                    downloadlink = json_data.getString("dlink");
                    records.add(record);

                }

            } catch (Exception e) {
                Log.e("ERROR", "Error pasting data " + e.toString());

            }

            return null;
        }

        protected void onPostExecute(Void result) {

        //  if (pd != null)
        //      pd.dismiss();// close dialog
            image.clearAnimation();
            image.setVisibility(View.GONE);
            adapter.notifyDataSetChanged();// notify the ListView to get new
                                            // records

            // statusAnim.setDuration(500);
            // statusAnim.start();

            // colorAnimation.setDuration(1000);
            // colorAnimation.start();

            if (oldVer < version) {
                ifUpdateAvailable();
            }
        }

        private void ifUpdateAvailable() {

            AlertDialog.Builder alertDialog = new AlertDialog.Builder(
                    FirstSelection.this);

            alertDialog.setPositiveButton("Yes", new OnClickListener() {

                @Override
                public void onClick(DialogInterface dialog, int which) {

                    dm = (DownloadManager) getSystemService(DOWNLOAD_SERVICE);
                    Request request = new Request(Uri.parse(downloadlink));
                    request.setDestinationInExternalPublicDir("/Download",
                            "Something_v1_1.apk");
                    enqueue = dm.enqueue(request);

                }
            });

            alertDialog.setNegativeButton("Later", null);

            alertDialog
                    .setMessage("A new version of something is available for download. Do you want to update now?");
            alertDialog.setTitle("something");
            alertDialog.show();

        }

        BroadcastReceiver receiver = new BroadcastReceiver() {

            @Override
            public void onReceive(Context context, Intent intent) {
                String action = intent.getAction();

                if (DownloadManager.ACTION_DOWNLOAD_COMPLETE.equals(action)) {
                    long downloadId = intent.getLongExtra(
                            DownloadManager.EXTRA_DOWNLOAD_ID, 0);
                    Query query = new Query();
                    query.setFilterById(enqueue);
                    Cursor c = dm.query(query);
                    if (c.moveToFirst()) {
                        int columnIndex = c
                                .getColumnIndex(DownloadManager.COLUMN_STATUS);
                        if (DownloadManager.STATUS_SUCCESSFUL == c
                                .getInt(columnIndex)) {

                            String uriString = c
                                    .getString(c
                                            .getColumnIndex(DownloadManager.COLUMN_LOCAL_URI));

                        }
                    }
                }
                registerReceiver(receiver, new IntentFilter(
                        DownloadManager.ACTION_DOWNLOAD_COMPLETE));

            }
        };

    }
}

Answer 1

在您的情况下，您无法保留 onCreate() 因为 AsyncTask doInBackground() 方法在工作线程中运行。

建议:1.

1. onCreate():运行AsyncTask

2. onStart() 检查 AsyncTask 状态，无论其任务是否完成。在 onPostExecte() 方法中完成后开始动画。 3.

3. 当您从 SecondActivity 返回时，如果 [onStart()] AsyncTask 完成其任务，它将开始动画。

示例

public class MyActivity extends Activity {
    BackTask backTask;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        // start AsyncTask
        backTask = new BackTask();
        backTask.execute();

    }

    @Override
    protected void onStart() {
        super.onStart();
        if (backTask.getStatus() == Status.FINISHED) {
            doAnimation();
        }
    }

    private void doAnimation() {
        // start animations
    }

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

        @Override
        protected Void doInBackground(Void... params) {
            // do web stuff
            return null;
        }

        @Override
        protected void onPostExecute(Void result) {
            super.onPostExecute(result);

            // fetches data now start anim
            doAnimation();

        }

    }

}