Android编码更高效和有效

Question

您好，我一直在研究我的第一个 Android 应用程序，但它开始变得有点缓慢和滞后。我以前做过 iPhone 应用程序，我知道我必须发布一些东西。所以我想我的问题是在避免内存泄漏方面为 android 编码的最佳实践是什么。从 JSON 提要加载数据，只是总体上简化我的代码以使其更有效地改善用户体验？

如果您能提供任何帮助，我将不胜感激，并对 android 充满热情，但我只想确保我做对了

到目前为止，这是我的代码示例

public class HomeActivity extends ListActivity {

    private MergeAdapter adapter=null;
    private ArrayAdapter<String> arrayAdapter=null;
    private ArrayAdapter<String> arrayAdapter2=null;
    private ArrayAdapter<String> arrayAdapter3=null;
    private static final String apiKey = "46fhr636gdbc737hjd92932dd"; 
    private static final String apiUser = "android-app-v1";
    private static final String ChosenTeam = null;
    private static String ChosenMethod = null; 
    public String fulldata = null;
    public String chosenLeagueId = "40";
    public List<String> newsList = null;
    public List<String> newsList2 = null;
    public List<String> newsList3 = null;

    public int newsAmount = 0;


    long unixTimeStamp = System.currentTimeMillis() / 1000L;

    //add Time Stamp to URL


    //public String chosenMethod; 


    String newsFeedRequest = "1.0/website/" + chosenLeagueId + "/news?timestamp=" + unixTimeStamp;
    String fixturesFeedURL = "https://website.com/_services/api/" + newsFeedRequest;
    private int container;


    private static String buildHmacSignature(String pKey, String pStringToSign)
    {
      String lSignature = "None";
      try
      {
        Mac lMac = Mac.getInstance("HmacSHA256");
        SecretKeySpec lSecret = new SecretKeySpec(pKey.getBytes(), "HmacSHA256");
        lMac.init(lSecret);

        byte[] lDigest = lMac.doFinal(pStringToSign.getBytes());
        BigInteger lHash = new BigInteger(1, lDigest);
        lSignature = lHash.toString(16);
        if ((lSignature.length() % 2) != 0) {
          lSignature = "0" + lSignature;
        }
      }
      catch (NoSuchAlgorithmException lEx)
      {
        throw new RuntimeException("Problems calculating HMAC", lEx);
      }
      catch (InvalidKeyException lEx)
      {
        throw new RuntimeException("Problems calculating HMAC", lEx);
      }

      return lSignature;
    }


    public void checkPreferences(){


        SharedPreferences preferences = getSharedPreferences("prefs", Context.MODE_PRIVATE);
        final String ChosenMethodPref = preferences.getString("ChosenMethod", ChosenMethod);
        Log.v("myapp", "ChosenMethod Home = " + ChosenMethodPref);

         if (ChosenMethodPref.equals("Team")) {
             setContentView(R.layout.homeactteam2);
             newsAmount = 5;

         } else {
             setContentView(R.layout.homeact);
             newsAmount = 10;
         }
}

    public void loadData(){String myhash = buildHmacSignature(apiKey, fixturesFeedURL);


    HttpClient client = new DefaultHttpClient();
    HttpPost post = new HttpPost(fixturesFeedURL);

    List<NameValuePair> pairs = new ArrayList<NameValuePair>();
    pairs.add(new BasicNameValuePair("requestToken", myhash));
    pairs.add(new BasicNameValuePair("apiUser", apiUser));

    try {
        post.setEntity (new UrlEncodedFormEntity(pairs));
        HttpResponse response = client.execute(post);
        BufferedReader reader = new BufferedReader(new InputStreamReader(response.getEntity().getContent(), "UTF-8"));
        String json = reader.readLine();
        fulldata = String.valueOf(json);
        Log.v("myApp","newsdata" + fulldata);

        newsList = new ArrayList<String>();
        newsList2 = new ArrayList<String>();
        newsList3 = new ArrayList<String>();

        JSONObject obj = new JSONObject(json);    
        JSONObject objData = obj.getJSONObject("data");
        JSONArray jArray = objData.getJSONArray("news");


           for(int t = 0; t < newsAmount; t++){
               JSONObject newsTitleDict = jArray.getJSONObject(t);

             newsList3.add(newsTitleDict.getString("title"));

           }

           for(int t = 0; t < 1; t++){
               JSONObject newsTitleDict = jArray.getJSONObject(t);

             newsList.add(newsTitleDict.getString("title"));
             newsList2.add(newsTitleDict.getString("title"));

           }



    } catch (ClientProtocolException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (JSONException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }


    arrayAdapter = new ArrayAdapter<String>(this, R.layout.single_item, newsList);
    arrayAdapter2 = new ArrayAdapter<String>(this, R.layout.single_item, newsList2);
    arrayAdapter3 = new ArrayAdapter<String>(this, R.layout.single_item, newsList3);

        ListView list = getListView();
           list.setTextFilterEnabled(true);

           LayoutInflater inflater = (LayoutInflater) this.getSystemService(Context.LAYOUT_INFLATER_SERVICE );
            View header = inflater.inflate( R.layout.homeheader, list, false);
            View header2 = inflater.inflate( R.layout.homeheader2, list, false);
            View header3 = inflater.inflate( R.layout.homeheader3, list, false);


    //setListAdapter (arrayAdapter);


        adapter = new MergeAdapter();
        adapter.addView(header);
        adapter.addAdapter(arrayAdapter);
        adapter.addView(header2);
        adapter.addAdapter(arrayAdapter2);
        adapter.addView(header3);
        adapter.addAdapter(arrayAdapter3);
        setListAdapter(adapter);

    }   
@Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);

        checkPreferences();
        loadData();


        Button backbtn = (Button) findViewById(R.id.backbtn);

        //Listening to button event
        backbtn.setOnClickListener(new View.OnClickListener() {

            public void onClick(View arg0) {
                //Starting a new Intent
                Intent previousScreen = new Intent(getApplicationContext(), ChooseTeamActivity.class);
                ChosenMethod = "null";
                SharedPreferences preferences = getSharedPreferences("prefs", Context.MODE_PRIVATE);
                SharedPreferences.Editor editor = preferences.edit();
                editor.putString("ChosenMethod", ChosenMethod);            
                editor.commit();
                previousScreen.putExtra("FullData", fulldata);
                startActivity(previousScreen);


            }
        });

    }


@Override
public boolean onCreateOptionsMenu(Menu menu) {
    MenuInflater inflater = getMenuInflater();
    inflater.inflate(R.menu.menu, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {

    if (item.getItemId() == R.id.home) {

        startActivity(new Intent(HomeActivity.this, HomeActivity.class));

        return(true);
  }


    if (item.getItemId() == R.id.match) {

        startActivity(new Intent(HomeActivity.this, MatchActivity.class));

        return(true);
  }



    if (item.getItemId() == R.id.teams) {

        startActivity(new Intent(HomeActivity.this, TeamsActivity.class));

        return(true);
  }



    if (item.getItemId() == R.id.twitter) {

        startActivity(new Intent(HomeActivity.this, TwitterActivity.class));

        return(true);
  }

    if (item.getItemId() == R.id.info) {

        startActivity(new Intent(HomeActivity.this, InfoActivity.class));

        return(true);
  }


    return(super.onOptionsItemSelected(item));


}

}

Answer 1

你应该看看这个 awesome presentation by Romain Guy .

它会让你深入了解你正在寻找的东西，你还会得到一些有用的提示:)

例如除了使用 AsyncTasks 和 Handlers 来避免 gui 线程过载之外，您还可以将大部分变量声明为 final .自定义 itemrenderer 实现将显着加快您的 gui(滚动)速度，并且 - 虽然这不是一个好的 Java 实践 - 使用直接引用而不是 getters 和 setters 也会有所改善性能。