Java NPE:CursorTreeAdapter$MyCursorHelper.changeCursor（光标，布尔值）和#x27；关于空对象引用

我试图用不同的游标从数据库中获取数据，并将其显示在由组分隔的ExpandableListView中。例如：

• 历史任务（到光标0）
  • 历史1
  • 历史2
• 地理任务（到光标1）
  • 地理1
  • 地理2
• 外语任务（至光标2）
  • 外语1
  • 外语2

我正试图使用CursorTreeAdapter来实现这一点，因为我的所有信息都在一个数据库中，它可以管理不同的游标，并在可扩展的ListView中正确显示信息

我遇到的问题是，我在代码的某个地方得到了一个NPE，但我无法检查它在哪里调试，因为它直接更改为另一个文件，而不知道发生了什么

当我在CursorTreeAdapter:：setChildrenCursor方法中调试时，就在我进入

childrenCursorHelper.changeCursor(childrenCursor, false);

它失败了，所以我不知道这个方法里面发生了什么

我的代码如下：

MtMainActivity.java

---

PS:Cursor工作正常，我使用唯一的ListView进行了检查，没有问题。

我的项目中也有同样的问题。看来，这是一个问题：

看看Android源代码中的方法：

    public void setChildrenCursor(int groupPosition, Cursor childrenCursor) {

    /*
     * Don't request a cursor from the subclass, instead we will be setting
     * the cursor ourselves.
     */
    MyCursorHelper childrenCursorHelper = getChildrenCursorHelper(groupPosition, false);

    /*
     * Don't release any cursor since we know exactly what data is changing
     * (this cursor, which is still valid).
     */
    childrenCursorHelper.changeCursor(childrenCursor, false);
}

在某些情况下，getChildrenCursorHelper将null返回到childrenCursorHelper。我通常在配置更改（例如屏幕旋转）后得到它

为了解决这个问题，我将CursorFilter+CursorTreeAdapter源添加到我的项目中，然后将空检查添加到childrenCursorHelper

    public void setChildrenCursor(int groupPosition, Cursor childrenCursor) {

    /*
     * Don't request a cursor from the subclass, instead we will be setting
     * the cursor ourselves.
     */
    MyCursorHelper childrenCursorHelper = getChildrenCursorHelper(groupPosition, false);

    /*
     * Don't release any cursor since we know exactly what data is changing
     * (this cursor, which is still valid).
     */
    if (childrenCursorHelper != null)
        childrenCursorHelper.changeCursor(childrenCursor, false);
}

最后，将我的适配器从fixedCursorTreeAdapter扩展到fixed

---

有关详细信息，请参阅。

您不需要向项目中添加CursorTreeAdapter源

只需覆盖setChildrenCursor：

public class MyAdapter extends CursorTreeAdapter {

    @Override
    public void setChildrenCursor(int groupPosition, Cursor childrenCursor) {
        try {
            Method getChildrenCursorHelper = CursorTreeAdapter.class.getDeclaredMethod("getChildrenCursorHelper", int.class, boolean.class);
            getChildrenCursorHelper.setAccessible(true);
            Object childrenCursorHelper = getChildrenCursorHelper.invoke(this, groupPosition, false);
            if (childrenCursorHelper != null) {
                Method changeCursor = childrenCursorHelper.getClass().getDeclaredMethod("changeCursor", Cursor.class, boolean.class);
                changeCursor.setAccessible(true);
                changeCursor.invoke(childrenCursorHelper, childrenCursor, false);
            }
        } catch (IllegalAccessException e) {
        } catch (InvocationTargetException e) {
        } catch (NoSuchMethodException e) {
        }
    }
}

at android.widget.CursorTreeAdapter.setChildrenCursor(CursorTreeAdapter.java:164)

    public void setChildrenCursor(int groupPosition, Cursor childrenCursor) {

    /*
     * Don't request a cursor from the subclass, instead we will be setting
     * the cursor ourselves.
     */
    MyCursorHelper childrenCursorHelper = getChildrenCursorHelper(groupPosition, false);

    /*
     * Don't release any cursor since we know exactly what data is changing
     * (this cursor, which is still valid).
     */
    childrenCursorHelper.changeCursor(childrenCursor, false);
}

    public void setChildrenCursor(int groupPosition, Cursor childrenCursor) {

    /*
     * Don't request a cursor from the subclass, instead we will be setting
     * the cursor ourselves.
     */
    MyCursorHelper childrenCursorHelper = getChildrenCursorHelper(groupPosition, false);

    /*
     * Don't release any cursor since we know exactly what data is changing
     * (this cursor, which is still valid).
     */
    if (childrenCursorHelper != null)
        childrenCursorHelper.changeCursor(childrenCursor, false);
}

public class MyAdapter extends CursorTreeAdapter {

    @Override
    public void setChildrenCursor(int groupPosition, Cursor childrenCursor) {
        try {
            Method getChildrenCursorHelper = CursorTreeAdapter.class.getDeclaredMethod("getChildrenCursorHelper", int.class, boolean.class);
            getChildrenCursorHelper.setAccessible(true);
            Object childrenCursorHelper = getChildrenCursorHelper.invoke(this, groupPosition, false);
            if (childrenCursorHelper != null) {
                Method changeCursor = childrenCursorHelper.getClass().getDeclaredMethod("changeCursor", Cursor.class, boolean.class);
                changeCursor.setAccessible(true);
                changeCursor.invoke(childrenCursorHelper, childrenCursor, false);
            }
        } catch (IllegalAccessException e) {
        } catch (InvocationTargetException e) {
        } catch (NoSuchMethodException e) {
        }
    }
}