Question

我当前正在制作一个android应用程序，现在我试图将此新的“ listingStatus”列添加到我的数据库中，我将该列名添加到了我的onCreate（）函数中，但是我仍然保持将其作为logCat。任何想法如何解决这个问题？我尝试删除数据库并重新创建它，但是我仍然遇到相同的错误。

package com.example.shareandcare;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

public class listingHelper extends SQLiteOpenHelper {
    public listingHelper(Context context) {
        super(context, "listing.db", null, 2);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL("create table listing(_id integer primary key autoincrement, listingTitle text, listingTag text, listingDescription text, listingDimensionX float, listingDimensionY float, listingDimensionZ float, listingImage text, listingStatus text)");
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion){
        db.execSQL("drop table if exists listing");
        onCreate(db);
    }

    public Cursor getAll() {
        return (getReadableDatabase().rawQuery("select _id, listingTitle, listingTag, listingDescription, listingDimensionX, listingDimensionY, listingDimensionZ, listingImage from listing order by listingTag", null));
    }

    public Cursor getAllConfirmed() {
        String arg = "1";
        String[] args = {arg};
        return (getReadableDatabase().rawQuery("select _id, listingTitle, listingTag, listingDescription, listingDimensionX, listingDimensionY, listingDimensionZ, listingImage from listing where listingStatus=?", args));
    }

    public Cursor getById(String id) {
        String[] args = {id};

        return (getReadableDatabase().rawQuery("select _id, listingTitle, listingTag, listingDescription, lisitngDimensionX, listingDimensionY, listingDimensionZ, listingImage from listing where _id=?", args));
    }

    public Cursor getByTitle(String title) {
        String[] args = {title};

        return (getReadableDatabase().rawQuery("select _id, listingTitle, listingTag, listingDescription, listingDimensionX, listingDimensionY, listingDimensionZ, listingImage from listing where listingTitle =?", args));
    }

    public Cursor getByTag(String tag) {
        tag = tag.toLowerCase();
        String[] args = {tag};

        return (getReadableDatabase().rawQuery("select _id, listingTitle, listingTag, listingDescription, listingDimensionX, listingDimensionY, lisitngDimensionZ, listingImage from listing where listingTag =?", args));
    }

    public void updateListingStatus(String title) {
        ContentValues cv = new ContentValues();
        String[] args ={title};

        cv.put("listingStatus", "1");
        getWritableDatabase().update("listing", cv, "title=?", args);
    }

    public void addListing(String listingTitle, String listingTag, String listingDescription, String listingDimensionX, String listingDimensionY, String listingDimensionZ, String listingImage) {
        ContentValues cv = new ContentValues();

        cv.put("listingTitle", listingTitle);
        cv.put("listingTag", listingTag.toLowerCase());
        cv.put("listingDescription", listingDescription);
        cv.put("listingDimensionX", listingDimensionX);
        cv.put("listingDimensionY", listingDimensionY);
        cv.put("listingDimensionZ", listingDimensionZ);
        cv.put("listingImage", listingImage);

        getWritableDatabase().insert("listing", "listingTitle", cv);
    }

    public void delete(String id) {
        String[] args = {id};
        getWritableDatabase().delete("listing","_id=?", args);
    }

    public void resetDatabase() {
        getWritableDatabase().execSQL("drop table if exists listing");
    }
}

这是我的logCat。

    --------- beginning of crash
2020-02-10 00:24:06.786 12602-12602/com.example.shareandcare E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.shareandcare, PID: 12602
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.shareandcare/com.example.shareandcare.admin}: android.database.sqlite.SQLiteException: no such column: listingStatus (code 1 SQLITE_ERROR): , while compiling: select _id, listingTitle, listingTag, listingDescription, listingDimensionX, listingDimensionY, listingDimensionZ, listingImage from listing where listingStatus=1
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3270)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016)
        at android.os.Handler.dispatchMessage(Handler.java:107)
        at android.os.Looper.loop(Looper.java:214)
        at android.app.ActivityThread.main(ActivityThread.java:7356)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
     Caused by: android.database.sqlite.SQLiteException: no such column: listingStatus (code 1 SQLITE_ERROR): , while compiling: select _id, listingTitle, listingTag, listingDescription, listingDimensionX, listingDimensionY, listingDimensionZ, listingImage from listing where listingStatus=1
        at android.database.sqlite.SQLiteConnection.nativePrepareStatement(Native Method)
        at android.database.sqlite.SQLiteConnection.acquirePreparedStatement(SQLiteConnection.java:986)
        at android.database.sqlite.SQLiteConnection.prepare(SQLiteConnection.java:593)
        at android.database.sqlite.SQLiteSession.prepare(SQLiteSession.java:590)
        at android.database.sqlite.SQLiteProgram.<init>(SQLiteProgram.java:61)
        at android.database.sqlite.SQLiteQuery.<init>(SQLiteQuery.java:37)
        at android.database.sqlite.SQLiteDirectCursorDriver.query(SQLiteDirectCursorDriver.java:46)
        at android.database.sqlite.SQLiteDatabase.rawQueryWithFactory(SQLiteDatabase.java:1443)
        at android.database.sqlite.SQLiteDatabase.rawQuery(SQLiteDatabase.java:1382)
        at com.example.shareandcare.listingHelper.getAllConfirmed(listingHelper.java:31)
        at com.example.shareandcare.admin.onCreate(admin.java:33)
        at android.app.Activity.performCreate(Activity.java:7825)
        at android.app.Activity.performCreate(Activity.java:7814)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1306)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3245)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409) 
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83) 
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016) 
        at android.os.Handler.dispatchMessage(Handler.java:107) 
        at android.os.Looper.loop(Looper.java:214) 
        at android.app.ActivityThread.main(ActivityThread.java:7356) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930) 
2020-02-10 00:24:06.814 12602-12602/com.example.shareandcare I/Process: Sending signal. PID: 12602 SIG: 9

Answer 1

您用于创建和删除表的SQL代码看起来有效。 logcat-log中有一行：“无此列”，这意味着您的“ getAllConfirmed”已执行，但您的迁移无法正常工作，因此请留意以下内容：

增加数据库的版本号，也许升级脚本没有执行（所以只需在超级构造函数调用中将“ 2”增加到“ 3”）
如果这不起作用，则可以从设备/仿真器中卸载应用程序，例如注释中提到的forpas。
设置断点，并查看是否执行了create table / upgrade命令

通常，如果要添加列，最好更改表并添加列。但是我想您只是应用程序的开始，并且您想让事情变得更简单，因此只要您尚未发布应用程序，您的方法就有效。

如果您刚刚开始，我只想让您知道，Android引入了一种新的数据库创建方法，该方法更常见，更简单：

https://developer.android.com/training/data-storage/room

这不能解决您的问题，但是如果您能够升级，则可以简化项目的数据库创建

Answer 2

只需添加，请始终添加一个null检查器，以防止应用程序崩溃。

简单：

if (null) {
 return "";
}

would go a long way

当我尝试加载数据库时，应用程序不断崩溃

2 个答案: