Question

我正在尝试从原始查询返回到我的SQLITE数据库的字符串。

问题是我正在桥接两个表，所以我不确定如何调用包含颜色的列（需要的值）。

如何从SQL查询返回字符串值到结果variable？

public String studentColor(){
    SQLiteDatabase db = getWritableDatabase();

    String queryStudent = "SELECT students.color FROM students, comments WHERE comments.author = students.name;";
    Cursor cursor = db.rawQuery(queryStudent, null);
    String result = // get students.color from cursor;
    return result
}

由于

修改

错误

E/AndroidRuntime: FATAL EXCEPTION: main
                  Process: com.example.me.echoboard, PID: 21552
                  java.lang.IllegalStateException: Could not execute method for android:onClick
                      at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:389)
                      at android.view.View.performClick(View.java:6213)
                      at android.widget.TextView.performClick(TextView.java:11074)
                      at android.view.View$PerformClick.run(View.java:23645)
                      at android.os.Handler.handleCallback(Handler.java:751)
                      at android.os.Handler.dispatchMessage(Handler.java:95)
                      at android.os.Looper.loop(Looper.java:154)
                      at android.app.ActivityThread.main(ActivityThread.java:6692)
                      at java.lang.reflect.Method.invoke(Native Method)
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1468)
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1358)
                   Caused by: java.lang.reflect.InvocationTargetException
                      at java.lang.reflect.Method.invoke(Native Method)
                      at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:384)
                      at android.view.View.performClick(View.java:6213) 
                      at android.widget.TextView.performClick(TextView.java:11074) 
                      at android.view.View$PerformClick.run(View.java:23645) 
                      at android.os.Handler.handleCallback(Handler.java:751) 
                      at android.os.Handler.dispatchMessage(Handler.java:95) 
                      at android.os.Looper.loop(Looper.java:154) 
                      at android.app.ActivityThread.main(ActivityThread.java:6692) 
                      at java.lang.reflect.Method.invoke(Native Method) 
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1468) 
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1358) 
                   Caused by: android.database.CursorIndexOutOfBoundsException: Index -1 requested, with a size of 0
                      at android.database.AbstractCursor.checkPosition(AbstractCursor.java:460)
                      at android.database.AbstractWindowedCursor.checkPosition(AbstractWindowedCursor.java:136)
                      at android.database.AbstractWindowedCursor.getString(AbstractWindowedCursor.java:50)
                      at com.example.me.echoboard.DBHandler.studentColor(DBHandler.java:121)
                      at com.example.me.echoboard.login.onClick(login.java:37)
                      at java.lang.reflect.Method.invoke(Native Method) 
                      at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:384) 
                      at android.view.View.performClick(View.java:6213) 
                      at android.widget.TextView.performClick(TextView.java:11074) 
                      at android.view.View$PerformClick.run(View.java:23645) 
                      at android.os.Handler.handleCallback(Handler.java:751) 
                      at android.os.Handler.dispatchMessage(Handler.java:95) 
                      at android.os.Looper.loop(Looper.java:154) 
                      at android.app.ActivityThread.main(ActivityThread.java:6692) 
                      at java.lang.reflect.Method.invoke(Native Method) 
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1468) 
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1358)

Answer 1

你没有在光标内移动，所以它位于-1（第一行之前）

使用以下内容移动到游标的第一行（如果有的话，如果不是空字符串将返回）： -

public String studentColor(){
    SQLiteDatabase db = getWritableDatabase();
    String result = ""; 

    String queryStudent = "SELECT students.color FROM students, comments WHERE comments.author = students.name;";
    Cursor cursor = db.rawQuery(queryStudent, null);
    if (cursor.moveToFirst()) {
        result = cursor.getString(cursor.getColumnIndex("students.color"));
    }
    cursor.close();
    return result
}

Answer 2

您需要做的是使用此更改查询，然后使用光标

"SELECT students.color as color FROM students, comments WHERE comments.author = students.name;";

光标

String result = cursor.getString(cursor.getColumnIndex("color"));

Android：在SQLITE中的原始查询后从游标获取字符串

2 个答案: