APP目前大概分
登入頁面->首頁->功能頁面
功能頁面會引用使用者打開APP開始輸入的帳號內容
新增功能傳送參數(如會員id)或是
照引用的帳號決定要顯示的內容(顯示會員id資料)

之前都是再登入介面抓值後跳頁面

s_id =(EditText)findViewById(R.id.number);//帳號
final String str = s_id.getText().toString().trim();//抓帳號值的字串

因為s_id並沒有儲存
倘若從功能介面上一頁再下一頁進去(重複幾次)
str抓的值就不見了，同時因為內容是空值引發錯誤導致系統停止回應

//Logcat檢察的錯誤
java.lang.NullPointerException: Attempt to invoke virtual method 'android.text.Editable android.widget.EditText.getText()' on a null object reference

嘗試用SharedPreferences儲存字串str.....
重複進入頁面和傳遞參數的次數變多了但還是有會跳出的風險

//登入頁面
package com.skypan.school;
import android.........

public class MainActivity extends AppCompatActivity {
    public static EditText s_id;//帳號
    public static EditText s_birth;//密碼
    public static TextView Login_text;//登入失敗顯示
    Button btn1;
    String url="http://‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧php";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Login_text =(TextView)findViewById(R.id.login_text);
        
        s_id =(EditText)findViewById(R.id.number);
        s_birth =(EditText)findViewById(R.id.password);
        final String str = s_id.getText().toString().trim();
        //字串str抓取輸入帳號的值
        btn1 = (Button) findViewById(R.id.btn_login);
        btn1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String o=DBphp_login.DBstring
                (s_id.getText().toString()
                ,s_birth.getText().toString()
                ,url);
                switch(o) {
                    case "GO"://帳密正確進入下一頁，並儲存字串str
                        SharedPreferences pref = getSharedPreferences
                        ("test", MODE_PRIVATE);
                        pref.edit()
                                .putString("USER", str)
                                .commit();
                                
                        Intent intent=
                        new Intent(MainActivity.this,Studenthome.class);
                        startActivity(intent); 
                        break;
                    default:
                        Login_text.setText("error");
                        break;
                        //帳密不正確，字串上顯示錯誤
                }
            }
        });
        }
}

//引用儲存的字串
 final String userid = getSharedPreferences("test", MODE_PRIVATE)
                .getString("USER", "");

實際測試抓到的仍是空值.......且出現了別的錯誤

顯式終止方法“關閉”未調用的情況

介面repair71行出錯

package com.skypan.school;

import ........

public class repair extends AppCompatActivity {
    public static TextView Last;
    String orderSting;//職位
    String url1="http:/‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧/";
    ListView LV1;
    String cookieStr;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_repair);
        //嘗試讀取SharedPreferences儲存的資料
         final String userid = getSharedPreferences
         ("test", MODE_PRIVATE).getString("USER", "");
        Log.v("log_tag=",userid);
        
        StrictMode.setThreadPolicy(new StrictMode.ThreadPolicy.Builder()
                .detectDiskReads()
                .detectDiskWrites()
                .detectNetwork()
                .penaltyLog()
                .build());
        StrictMode.setVmPolicy(new StrictMode.VmPolicy.Builder()
                .detectLeakedClosableObjects()
                .penaltyLog()
                .penaltyDeath()
                .build());
        Handler myHandler = new Handler();
        myHandler.postDelayed(runTimerStop, 2000);
        if(cookieStr!=null){
            myHandler.removeCallbacks(runTimerStop);
        }  
        
        String r = DBstring.DB1("select * from text1");//匯出資料
        TextView TV=(TextView) findViewById(R.id.Last);
        int integer = Integer.valueOf(r);
        if(integer > 0)
        {
            orderSting ="1";
        }else{
            orderSting = "0";
        }
        LV1 = (ListView) findViewById(R.id.LV1); 

        //新增資料:↓新增按鈕功能
        Button b1 = (Button) findViewById(R.id.button);
        b1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String[] et0= new String[]{userid,orderSting};//
                Inphp.Interting(et0,url1);//
            }
        });
    }
    private Runnable runTimerStop=new Runnable() {
        @Override
        public void run() {
            select(null);
        }
    };
    //顯示表單資料
    public void select(String id) {
        try {
            String r = DBphp.DBstring(id, url1);
            JSONArray jsonArray = new JSONArray(r);
            List<Map<String, Object>> items = 
            new ArrayList<Map<String, Object>>();

            for (int i = 0; i < jsonArray.length(); i++) {
                JSONObject jsonData = jsonArray.getJSONObject(i);
                Map<String, Object> item = new HashMap<String, Object>(); 
                item.put("date", jsonData.getString("date"));//日期
                item.put("time",jsonData.getString("time"));//時段
                item.put("state",jsonData.getString("state"));//職務
                item.put("place",jsonData.getString("place"));//地點
                items.add(item);// 新增到items
            }
            //在此輸入ListView自訂畫面，本教學為list_text.xml檔案
            SimpleAdapter SA = new SimpleAdapter(this, items, 
            R.layout.list_text, new String[]{"date","time","state","place"}
            , new int[]{R.id.text0, R.id.text1, R.id.text2, R.id.text3});
            LV1.setAdapter(SA);  
        } catch (Exception e) {
            Log.e("log_tag=", e.toString());
        }
    }
 }

設定連結的DBstring檔28行

package com.skypan.school.ui;
import 
//此Java檔案做連結
public class DBstring {
    public static String DB1(String i){
        String result="";     
        try {
            HttpClient HC=new DefaultHttpClient();
            HttpPost HP =new 
            HttpPost("http://192.192.125.197/ysp105s02/TTEST/Last.php");
            ArrayList<NameValuePair> params = new ArrayList<NameValuePair>();
            params.add(new BasicNameValuePair("S1",i));
            HP.setEntity(new UrlEncodedFormEntity(params, HTTP.UTF_8));
            HttpResponse HR=HC.execute(HP);   
            result= EntityUtils.toString(HR.getEntity(),HTTP.UTF_8);
        }catch (Exception e){
        Log.i("錯誤訊息",e.toString());
        }
        return result;
    }
}

不知道是不是因為SharedPreferences用的不對才會引發的錯誤......
再加上repair介面的button按下傳遞參數後，userid傳遞的是空值
貌似也沒儲存到的樣子.......