Question

我需要扩展 ListView来创建自定义组件。我想把搜索按钮放在左下角浮动。当我在onMessure中运行生成错误时。

此代码是一个片段，原始代码还有许多其他内容。

我尝试将ViewGroup父级更改为null，但是我收到了同样的错误。

mPainelView = inflater.inflate(R.layout.longlist_painel, null);

自定义视图：

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="horizontal" >

<ImageButton
    android:id="@+id/longlist_painel_seek"
    android:layout_width="48dp"
    android:layout_height="48dp"
    android:src="@android:drawable/ic_menu_search" /></FrameLayout>

扩展ListView：

public class List2 extends ListView {
    private View mPainelView;

    private int mPainelViewWidth;
    private int mPainelViewHeight;

    public List2(Context context) {
        super(context);
        createPainel();
    }

    public List2(Context context, AttributeSet attrs) {
        super(context, attrs);
        createPainel();
    }

    public List2(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        createPainel();
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        if (mPainelView != null) {
            measureChild(mPainelView, widthMeasureSpec, heightMeasureSpec);
            mPainelViewWidth = mPainelView.getMeasuredWidth();
            mPainelViewHeight = mPainelView.getMeasuredHeight();
        }
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        super.onLayout(changed, l, t, r, b);
        if (mPainelView != null) {
            mPainelView.layout(0, this.getBottom()-mPainelViewHeight,  mPainelViewWidth, mPainelViewHeight);
        }
    }

    @Override
    protected void dispatchDraw(Canvas canvas) {
        super.dispatchDraw(canvas);
        drawChild(canvas, mPainelView, getDrawingTime());
    }


    private void createPainel(){
        LayoutInflater inflater = (LayoutInflater) getContext()
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);

        mPainelView = inflater.inflate(R.layout.longlist_painel, this);
    }
}

错误：

java.lang.NullPointerException
at android.view.ViewGroup.measureChild(ViewGroup.java:3098)
at com.rodrigo.comp.LongList2.onMeasure(List2.java:40)
at android.view.View.measure(View.java:8173)

Answer 1

您不需要扩展ListView，您可以使用RelativeLayout将视图放在彼此之上：

<RelativeLayout
    android:layout_width="fill_parent"
    android:layout_height="fill_parent" 
    >
    <ListView
        android:layout_width="fill_parent"
        android:layout_height="fill_parent" 
        />        
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" 
        android:layout_alignParentLeft="true"
        android:layout_alignParentBottom="true"
        android:padding="10dp"
        android:text="Search"
        />
</RelativeLayout>

Answer 2

首先我的英语不是我的母语，我同时遇到同样的问题，所以我用Google搜索并找到你，当它调用“measurChild”时，nullpointer异常被抛出，我发现你的mPainelView' s layoutParams为null，因此异常抛出。

如果你将inflate方法更改为“inflater.inflate（R.layout.longlist_painel，yourlistview，false）;”

你可以解决这个问题

将自定义视图放在另一个视图中

2 个答案: