如何比較用戶在EditText中輸入的數據並從android studio 2.0中的sqlite數據庫中檢索EditText中的結果數據

Question

我正在學習android。 我正在嘗試創建一個在EditText中從用戶獲取數據的應用程序。 將該數據比較到SQLite數據庫中，然后在另一個EditText中返回數據。

運行我的代碼后，應用程序即關閉ieForce。 即不幸的是您的應用程序已關閉。 請幫助我比較和檢索sqlite數據庫中的數據，並將其顯示在EditText中。

    My Code is:
DatabaseHelper Class:
     public Cursor getData() {
            SQLiteDatabase db = this.getWritableDatabase();
            String english = et1.getText().toString();

//查詢查詢數據庫中的數據

Cursor cursor = db.rawQuery("select MSICTm_AutoTarget_Word from" + TABLE_NAME + "where MDICTm_Source_Word="+english, null);
            et2.setText("");
            if (cursor!=null) {
                cursor.moveToFirst();
                do {
                    String MSICTm_AutoTarget_Word = cursor.getString(cursor.getColumnIndex("MSICTm_AutoTarget_Word"));
                    et2.append("MSICTm_AutoTarget_Word"+cursor.getString(2)+cursor);
                } while (cursor.moveToNext());
            }
     return cursor;
            }         

主要活動類別：

public void viewData() {
        b1.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                Cursor cursor = mydb.getData();
                if (cursor != null) {
                    if (cursor.moveToFirst()) {
                        do {
                            String MSICTm_AutoTarget_Word = cursor.getString(cursor.getColumnIndex("MSICTm_AutoTarget_Word"));
                            et2.append("MSICTm_AutoTarget_Word" + MSICTm_AutoTarget_Word + cursor);
                        }
                        while (cursor.moveToNext());
                    }
                }
            }
 });
    }

// Logcat

04-27 14:10:34.698 2420-2420/com.example.mcsipl_hplaptop240_1.language I/art: Not late-enabling -Xcheck:jni (already on)
04-27 14:10:34.826 2420-2420/com.example.mcsipl_hplaptop240_1.language W/System: ClassLoader referenced unknown path: /data/app/com.example.mcsipl_hplaptop240_1.language-1/lib/x86
04-27 14:10:44.248 2420-2420/com.example.mcsipl_hplaptop240_1.language W/System: ClassLoader referenced unknown path: /data/app/com.example.mcsipl_hplaptop240_1.language-1/lib/x86
04-27 14:10:45.466 2420-2420/com.example.mcsipl_hplaptop240_1.language W/art: Verification of android.support.v7.view.ActionMode android.support.v7.app.AppCompatDelegateImplV7.startSupportActionModeFromWindow(android.support.v7.view.ActionMode$Callback) took 369.473ms
04-27 14:10:45.677 2420-2426/com.example.mcsipl_hplaptop240_1.language W/art: Suspending all threads took: 104.833ms
04-27 14:10:46.390 2420-2430/com.example.mcsipl_hplaptop240_1.language W/art: Suspending all threads took: 525.430ms
04-27 14:10:46.398 2420-2430/com.example.mcsipl_hplaptop240_1.language I/art: Background sticky concurrent mark sweep GC freed 15945(1793KB) AllocSpace objects, 8(176KB) LOS objects, 66% free, 1257KB/3MB, paused 526.247ms total 537.371ms
04-27 14:10:46.713 2420-2426/com.example.mcsipl_hplaptop240_1.language W/art: Suspending all threads took: 137.656ms
04-27 14:10:47.051 2420-2420/com.example.mcsipl_hplaptop240_1.language W/art: Before Android 4.1, method android.graphics.PorterDuffColorFilter android.support.graphics.drawable.VectorDrawableCompat.updateTintFilter(android.graphics.PorterDuffColorFilter, android.content.res.ColorStateList, android.graphics.PorterDuff$Mode) would have incorrectly overridden the package-private method in android.graphics.drawable.Drawable
04-27 14:10:47.300 2420-2426/com.example.mcsipl_hplaptop240_1.language W/art: Suspending all threads took: 223.122ms
04-27 14:10:48.227 2420-2426/com.example.mcsipl_hplaptop240_1.language W/art: Suspending all threads took: 149.071ms
04-27 14:10:48.748 2420-2426/com.example.mcsipl_hplaptop240_1.language W/art: Suspending all threads took: 166.289ms
04-27 14:10:48.913 2420-2420/com.example.mcsipl_hplaptop240_1.language W/FileUtils: Failed to chmod(/data/user/0/com.example.mcsipl_hplaptop240_1.language/databases/LNGTRNS.db): android.system.ErrnoException: chmod failed: EPERM (Operation not permitted)
04-27 14:10:48.914 2420-2420/com.example.mcsipl_hplaptop240_1.language D/AndroidRuntime: Shutting down VM


                                                                                         --------- beginning of crash
04-27 14:10:48.914 2420-2420/com.example.mcsipl_hplaptop240_1.language E/AndroidRuntime: FATAL EXCEPTION: main
                                                                                         Process: com.example.mcsipl_hplaptop240_1.language, PID: 2420
                                                                                         java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.mcsipl_hplaptop240_1.language/com.example.mcsipl_hplaptop240_1.language.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
                                                                                             at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
                                                                                             at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
                                                                                             at android.app.ActivityThread.-wrap11(ActivityThread.java)
                                                                                             at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
                                                                                             at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                                             at android.os.Looper.loop(Looper.java:148)
                                                                                             at android.app.ActivityThread.main(ActivityThread.java:5417)
                                                                                             at java.lang.reflect.Method.invoke(Native Method)
                                                                                             at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                                                                                             at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
                                                                                          Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
                                                                                             at com.example.mcsipl_hplaptop240_1.language.MainActivity.viewData(MainActivity.java:87)
                                                                                             at com.example.mcsipl_hplaptop240_1.language.MainActivity.onCreate(MainActivity.java:34)
                                                                                             at android.app.Activity.performCreate(Activity.java:6237)
                                                                                             at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
                                                                                             at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
                                                                                             at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
                                                                                             at android.app.ActivityThread.-wrap11(ActivityThread.java) 
                                                                                             at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) 
                                                                                             at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                                             at android.os.Looper.loop(Looper.java:148) 
                                                                                             at android.app.ActivityThread.main(ActivityThread.java:5417) 
                                                                                             at java.lang.reflect.Method.invoke(Native Method) 
                                                                                             at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
                                                                                             at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 

Answer 1

您是否已在主要活動中初始化dbhelper類？

dbclass mydb=new dbclass();

Answer 2

您的錯誤似乎是

原因：java.lang.NullPointerException：嘗試在空對象引用上調用虛擬方法'void android.widget.Button.setOnClickListener（android.view.View $ OnClickListener）'

在viewData（）方法中設置onClickListener時，按鈕b1尚未初始化。

初始化按鈕b1

b1 = (Button) findViewbyId(R.id.your_button_id);

設置點擊監聽器之前