Question

DBAdapter类函数：

public void getValues(){

        Cursor mCursor = db.query(DBAdapter.DATABASE_TABLE2, new String[] {
                EDGE_ID,
                SOURCE_NODE_ID,
                DESTINATION_NODE_ID,
                VALUE1}, null, null, null, null, null);
        mCursor.moveToFirst();
        while(!mCursor.isAfterLast()) {
            mArrayList.add(mCursor.getString(mCursor.getColumnIndex(DBAdapter.SOURCE_NODE_ID)));
            mCursor.moveToNext();
        }

        for(String d1:mArrayList) {
            System.out.println(d1);
        }
    }

以下是主要活动类：

public void onCreate(Bundle icicle) {
        super.onCreate(icicle);
        setContentView(R.layout.main);

    final DBAdapter db = new DBAdapter(this);
    db.open();
    db.getValues();
    db.close();
}

根据上面的代码，我应该得到一个数组列表，其中包含我的数据库表的值

SOURCE_NODE_ID

属性。我想在LogCat中打印这个arraylist。但我得到以下错误：

05-30 14:51:39.435: E/AndroidRuntime(4954): FATAL EXCEPTION: main
05-30 14:51:39.435: E/AndroidRuntime(4954): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.navigationsystem/com.navigationsystem.NavigationSystemActivity}: java.lang.NullPointerException
05-30 14:51:39.435: E/AndroidRuntime(4954):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956)
05-30 14:51:39.435: E/AndroidRuntime(4954):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
05-30 14:51:39.435: E/AndroidRuntime(4954):     at android.app.ActivityThread.access$600(ActivityThread.java:123)
05-30 14:51:39.435: E/AndroidRuntime(4954):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
05-30 14:51:39.435: E/AndroidRuntime(4954):     at android.os.Handler.dispatchMessage(Handler.java:99)
05-30 14:51:39.435: E/AndroidRuntime(4954):     at android.os.Looper.loop(Looper.java:137)
05-30 14:51:39.435: E/AndroidRuntime(4954):     at android.app.ActivityThread.main(ActivityThread.java:4424)
05-30 14:51:39.435: E/AndroidRuntime(4954):     at java.lang.reflect.Method.invokeNative(Native Method)
05-30 14:51:39.435: E/AndroidRuntime(4954):     at java.lang.reflect.Method.invoke(Method.java:511)
05-30 14:51:39.435: E/AndroidRuntime(4954):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
05-30 14:51:39.435: E/AndroidRuntime(4954):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
05-30 14:51:39.435: E/AndroidRuntime(4954):     at dalvik.system.NativeStart.main(Native Method)
05-30 14:51:39.435: E/AndroidRuntime(4954): Caused by: java.lang.NullPointerException
05-30 14:51:39.435: E/AndroidRuntime(4954):     at com.navigationsystem.DBAdapter.getValues(DBAdapter.java:117)
05-30 14:51:39.435: E/AndroidRuntime(4954):     at com.navigationsystem.NavigationSystemActivity.onCreate(NavigationSystemActivity.java:53)
05-30 14:51:39.435: E/AndroidRuntime(4954):     at android.app.Activity.performCreate(Activity.java:4465)
05-30 14:51:39.435: E/AndroidRuntime(4954):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
05-30 14:51:39.435: E/AndroidRuntime(4954):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920)
05-30 14:51:39.435: E/AndroidRuntime(4954):     ... 11 more

此代码有什么问题。

感谢。

Answer 1

05-30 14:51:39.435: E/AndroidRuntime(4954): Caused by: java.lang.NullPointerException 
05-30 14:51:39.435: E/AndroidRuntime(4954):     at com.navigationsystem.DBAdapter.getValues(DBAdapter.java:117)

您的代码中有NullPointer。

我认为mArrayList方法中的null为getValue()。你在哪里创建那个List？

db也可能null DBAdapter。{{1}}你试过调试吗？你输出了变量吗？

ArrayList值未在LogCat中打印

1 个答案: