使用SharedPreferences ...我做對了嗎？

我有一個子菜單，包含3個用戶選擇。選擇時，每個選項調用的以下3個功能之一：使用SharedPreferences ...我做對了嗎？

void viewLast5Packets() 
{ 
    userDefinedCount = 4; 
    prefEditor.putString(lastpacketsPHP, "/* Put PHP file link here */"); 
    prefEditor.commit(); 
    assignInfoToHistoryTextView(); 
} 

void viewLast10Packets() 
{ 
    userDefinedCount = 9; 
    prefEditor.putString(lastpacketsPHP, "/* Put PHP file link here */"); 
    prefEditor.commit(); 
    assignInfoToHistoryTextView(); 
} 

void viewLast20Packets() 
{ 
    userDefinedCount = 19; 
    prefEditor.putString(lastpacketsPHP, "/* Put PHP file link here */"); 
    prefEditor.commit(); 
    assignInfoToHistoryTextView(); 
}

每個功能創建名爲lastpacketsPHP共享偏好，並把不同的URL到所述偏好。當調用assignInfoToHistoryTextView時，它調用位於不同類文件中的另一個函數。該類如下所示：

package shc_BalloonSat.namespace; 

import java.text.DecimalFormat; 

import org.json.JSONArray; 
import org.json.JSONException; 
import org.json.JSONObject; 

import android.app.Activity; 
import android.content.SharedPreferences; 
import android.content.SharedPreferences.Editor; 
import android.os.Bundle; 
import android.util.Log; 
import android.view.Menu; 
import android.view.MenuInflater; 
import android.view.MenuItem; 
import android.view.SubMenu; 
import android.widget.TextView; 
import android.widget.Toast; 

public class Shc_BalloonSat_Activity extends Activity 
{ 
int historyCountFromUser; 
httpAPI api = new httpAPI(this); 
kmlAPI kml = new kmlAPI(this); 
DecimalFormat df = new DecimalFormat("##.#####"); 
DecimalFormat decimalf = new DecimalFormat("##.######"); 
SharedPreferences pref; 
Editor prefEditor; 
String lastpacketsPHP; 

// User to determine how many packet the user would like to see. 
int userDefinedCount = 4; 

/** Called when the activity is first created. 
* @param view */ 

@Override 
public void onCreate(Bundle savedInstanceState) 
{ 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.main); 
    String returned = null; 
    prefEditor.putString(lastpacketsPHP, "http://www.wktechnologies.com/shc_android_app/get_last_5_BS_packets.php"); 

    try 
    { 
     returned = api.getData(); 
    } 

    catch (Exception e) 
    { 
     e.printStackTrace(); 
    } 

    TextView infoTV = (TextView)this.findViewById(R.id.info); 
    infoTV.setText(returned); 
    assignInfoToInfoTextView(); 
    assignInfoToHistoryTextView(); 
} 

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

    SubMenu submenu = menu.addSubMenu(0, Menu.FIRST, Menu.NONE, "Preferences"); 
    submenu.add(0, 5, Menu.NONE, "Get Last 5 Packets"); 
    submenu.add(0, 10, Menu.NONE, "Get Last 10 Packets"); 
    submenu.add(0, 20, Menu.NONE, "Get Last 20 Packets"); 
    inflater.inflate(R.menu.mainmenu, submenu); 

    return true; 
} 

@Override 
public boolean onOptionsItemSelected(MenuItem item) 
{ 
    // Handle item selection 
    switch (item.getItemId()) 
    { 
     case R.id.viewKML: 
      viewKML(); 
      return true; 
     case 5: 
      viewLast5Packets(); 
      return true; 
     case 10: 
      viewLast10Packets(); 
      return true; 
     case 20: 
      viewLast5Packets(); 
      return true; 
     default: 
      return super.onOptionsItemSelected(item); 
    } 
} 

public void assignInfoToInfoTextView() 
{ 
    TextView infoTV = (TextView)this.findViewById(shc_BalloonSat.namespace.R.id.info); 

    try 
    { 
     JSONArray jArray = new JSONArray(api.result); 
     for (int count = 0; count < 2; count++) 
     { 
      JSONObject json_data = jArray.getJSONObject(count); 

      double altitudeData = json_data.getDouble("altitude"); 
      String infoText = "Last Known Altitude: " + df.format(altitudeData) + "\n"; 

      Double speedData = json_data.optDouble("speed"); 

      if (speedData.isNaN()) 
      { 
       speedData = 0.00; 
      } 

      infoText += "Last Known Speed: " + df.format(speedData) + "\n"; 

      double recentLatitudeData = json_data.getDouble("latitude"); 
      infoText += "Last Known Latitude: " + df.format(recentLatitudeData) + "\n"; 

      double recentLongitudeData = json_data.getDouble("longitude"); 
      infoText += "Last Known Longtitude: " + df.format(recentLongitudeData) + "\n"; 

      infoTV.setText(infoText); 
     } 
    } 

    catch (JSONException e) 
    { 
     // TODO Auto-generated catch block 
     Log.e("<tag>", e.getMessage()); 
     Toast.makeText(this,"Error in (Last Known) method!",Toast.LENGTH_SHORT).show(); 
    } 
} 

public void assignInfoToHistoryTextView() 
{ 
    try 
    { 
     JSONArray jArray = new JSONArray(api.result); 

     for (int count = 1; count <= userDefinedCount; count++) 
     { 
      TextView historyTV = (TextView)this.findViewById(shc_BalloonSat.namespace.R.id.history); 
      JSONObject json_data = jArray.getJSONObject(count); 

      double altitudeData = json_data.getDouble("altitude"); 
      String historyText = "Altitude: " + decimalf.format(altitudeData) + "\n"; 

      Double speedData = json_data.optDouble("speed"); 

      if (speedData.isNaN()) 
      { 
       speedData = 0.00; 
      } 

      historyText += "Speed: " + df.format(speedData) + "\n"; 

      double latitudeData = json_data.getDouble("latitude"); 
      historyText += "Latitude: " + df.format(latitudeData) + "\n"; 

      double longitudeData = json_data.getDouble("longitude"); 
      historyText += "Longtitude: " + df.format(longitudeData) + "\n\n"; 

      historyTV.append(historyText); 
     } 
    } 

    catch (JSONException e) 
    { 
     // TODO Auto-generated catch block 
     Log.e("log_tag", "Error parsing data: " + e.toString()); 
    } 

} 

void viewLast5Packets() 
{ 
    userDefinedCount = 4; 
    prefEditor.putString(lastpacketsPHP, "http://www.wktechnologies.com/shc_android_app/get_last_5_BS_packets.php"); 
    prefEditor.commit(); 
    assignInfoToHistoryTextView(); 
} 

void viewLast10Packets() 
{ 
    userDefinedCount = 9; 
    prefEditor.putString(lastpacketsPHP, "http://www.wktechnologies.com/shc_android_app/get_last_10_BS_packets.php"); 
    prefEditor.commit(); 
    assignInfoToHistoryTextView(); 
} 

void viewLast20Packets() 
{ 
    userDefinedCount = 19; 
    prefEditor.putString(lastpacketsPHP, "http://www.wktechnologies.com/shc_android_app/get_last_20_BS_packets.php"); 
    prefEditor.commit(); 
    assignInfoToHistoryTextView(); 
} 

public void viewKML() 
{ 
    kml.openKML(); 
} 
}

在httpPost我想設置它，這樣它會調用哪個PHP文件取決於由用戶選擇什麼選項進行選擇。我通過插入獲取首選項的值並將其放入httpPost中來完成此操作。當我在模擬器中運行應用程序時，它會立即崩潰，直到我將優先選擇代碼放入httpPost中才會發生，所以我知道我的語法錯誤，我只是不知道我在做什麼錯誤。任何幫助將不勝感激。

我在運行時得到這些錯誤與上面的代碼：

02-02 13:42:14.973: E/AndroidRuntime(230): Uncaught handler: thread main exiting due to uncaught exception 
02-02 13:42:15.213: D/dalvikvm(230): GC freed 3178 objects/319424 bytes in 131ms 
02-02 13:42:15.283: E/AndroidRuntime(230): java.lang.StackOverflowError 
02-02 13:42:15.283: E/AndroidRuntime(230): at java.lang.Thread.currentThread(Thread.java:588) 
02-02 13:42:15.283: E/AndroidRuntime(230): at java.lang.ThreadLocal.get(ThreadLocal.java:59) 
02-02 13:42:15.283: E/AndroidRuntime(230): at android.os.Looper.myLooper(Looper.java:137) 
02-02 13:42:15.283: E/AndroidRuntime(230): at android.os.Handler.<init>(Handler.java:119) 
02-02 13:42:15.283: E/AndroidRuntime(230): at android.app.Activity.<init>(Activity.java:673) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.Shc_BalloonSat_Activity.<init>(Shc_BalloonSat_Activity.java:21) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.httpAPI.<init>(httpAPI.java:20) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.Shc_BalloonSat_Activity.<init>(Shc_BalloonSat_Activity.java:24) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.httpAPI.<init>(httpAPI.java:20) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.Shc_BalloonSat_Activity.<init>(Shc_BalloonSat_Activity.java:24) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.httpAPI.<init>(httpAPI.java:20) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.Shc_BalloonSat_Activity.<init>(Shc_BalloonSat_Activity.java:24) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.httpAPI.<init>(httpAPI.java:20) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.Shc_BalloonSat_Activity.<init>(Shc_BalloonSat_Activity.java:24) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.httpAPI.<init>(httpAPI.java:20) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.Shc_BalloonSat_Activity.<init>(Shc_BalloonSat_Activity.java:24) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.httpAPI.<init>(httpAPI.java:20) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.Shc_BalloonSat_Activity.<init>(Shc_BalloonSat_Activity.java:24) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.httpAPI.<init>(httpAPI.java:20) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.Shc_BalloonSat_Activity.<init>(Shc_BalloonSat_Activity.java:24) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.httpAPI.<init>(httpAPI.java:20) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.Shc_BalloonSat_Activity.<init>(Shc_BalloonSat_Activity.java:24) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.httpAPI.<init>(httpAPI.java:20) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.Shc_BalloonSat_Activity.<init>(Shc_BalloonSat_Activity.java:24) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.httpAPI.<init>(httpAPI.java:20) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.Shc_BalloonSat_Activity.<init>(Shc_BalloonSat_Activity.java:24) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.httpAPI.<init>(httpAPI.java:20) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.Shc_BalloonSat_Activity.<init>(Shc_BalloonSat_Activity.java:24) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.httpAPI.<init>(httpAPI.java:20) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.Shc_BalloonSat_Activity.<init>(Shc_BalloonSat_Activity.java:24) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.httpAPI.<init>(httpAPI.java:20) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.Shc_BalloonSat_Activity.<init>(Shc_BalloonSat_Activity.java:24) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.httpAPI.<init>(httpAPI.java:20) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.Shc_BalloonSat_Activity.<init>(Shc_BalloonSat_Activity.java:24) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.httpAPI.<init>(httpAPI.java:20) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.Shc_BalloonSat_Activity.<init>(Shc_BalloonSat_Activity.java:24) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.httpAPI.<init>(httpAPI.java:20) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.Shc_BalloonSat_Activity.<init>(Shc_BalloonSat_Activity.java:24) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.httpAPI.<init>(httpAPI.java:20) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.Shc_BalloonSat_Activity.<init>(Shc_BalloonSat_Activity.java:24) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.httpAPI.<init>(httpAPI.java:20) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.Shc_BalloonSat_Activity.<init>(Shc_BalloonSat_Activity.java:24) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.httpAPI.<init>(httpAPI.java:20) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.Shc_BalloonSat_Activity.<init>(Shc_BalloonSat_Activity.java:24) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.httpAPI.<init>(httpAPI.java:20) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.Shc_BalloonSat_Activity.<init>(Shc_BalloonSat_Activity.java:24) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.httpAPI.<init>(httpAPI.java:20) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.Shc_BalloonSat_Activity.<init>(Shc_BalloonSat_Activity.java:24) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.httpAPI.<init>(httpAPI.java:20) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.Shc_BalloonSat_Activity.<init>(Shc_BalloonSat_Activity.java:24) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.httpAPI.<init>(httpAPI.java:20) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.Shc_BalloonSat_Activity.<init>(Shc_BalloonSat_Activity.java:24) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.httpAPI.<init>(httpAPI.java:20) 
02-02 13:42:15.283: E/AndroidRuntime(230): at shc_BalloonSat.namespace.Shc_BalloonSat_Activity.<init>(Shc_BalloonSat_Activity. 

02-02 13:42:15.373: I/dalvikvm(230): threadid=7: reacting to signal 3 
02-02 13:42:15.373: E/dalvikvm(230): Unable to open stack trace file '/data/anr/traces.txt': Permission denied

來源

2012-02-02 tylerbhughes

public class httpAPI 
{ 
    Shc_BalloonSat_Activity shc; 

    ... 

     httppost = new HttpPost(shc.pref.getString(shc.lastpacketsPHP, 
           shc.lastpacketsPHP.toString()));

最初，麻煩的是，如果沒有被初始化正在使用SHC。繼續提出這個問題，因爲HttpPost對象需要一個SharedPreferences實例（可通過上下文訪問），所以我建議在httpAPI類中添加一個構造函數。例如：

public class httpAPI { 

    Shc_BalloonSat_Activity shc; 
    HttpPost httppost; 

    ... 

    public httpAPI(Shc_BalloonSat_Activity aContext) { 
     shc = aContext; 
    } 

    ... 

    public String getData() throws Exception { 
     ... 
     httppost = new HttpPost(shc.pref.getString(shc.lastpacketsPHP, shc.lastpacketsPHP.toString());

來源

2012-02-02 03:28:24 Pedantic

我添加了一個構造函數來SHC和加載時它仍然立即崩潰。 – tylerbhughes 2012-02-02 14:26:46

你能用你用來設置shc的代碼更新你的例子嗎？ – Pedantic 2012-02-02 14:31:48

當然，現在已經更新了。 – tylerbhughes 2012-02-02 14:49:56

使用SharedPreferences ...我做對了嗎？

回答

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