BaseAdapter之getItemViewType返回值问题

问题描述

给ListView的item指定不同的布局，Adapter继承BaseAdapter并复写以下两个方法：

/**
 * 返回 有几种item布局
 * @return
 */
@Override
public int getViewTypeCount() {
    return TYPE_COUNT;
}

@Override
public int getItemViewType(int position) {
    if (condition) {
        return TYPE_1;
    }
    return TYPE_2;
}

我的TYPE_1和TYPE_2是这样定义的：

private final int TYPE_COUNT = 2;
private final int TYPE_1 = 1;
private final int TYPE_2 = 2;

然后在getView中通过getItemViewType(position)返回值来判断加载哪种布局：

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    ViewHolder1 viewHolder1 = null;
    ViewHolder2 viewHolder2 = null;

    int currentType = getItemViewType(position);
    if (convertView == null) {
        switch (currentType) {
            case TYPE_1:
                convertView = mLayoutInflater.inflate(R.layout.simple_item_1, null);
                viewHolder1 = new ViewHolder1();
                viewHolder1.imageView = (ImageView) convertView.findViewById(R.id.imgview);
                convertView.setTag(viewHolder1);
                break;

            case TYPE_2:
                convertView = mLayoutInflater.inflate(R.layout.simple_item_2, null);
                viewHolder2 = new ViewHolder2();
                viewHolder2.textView = (TextView) convertView.findViewById(R.id.textview);
                convertView.setTag(viewHolder2);
                break;
        }
    } else {
        switch (currentType) {
            case TYPE_1:
                viewHolder1 = (ViewHolder1) convertView.getTag();
                break;
            case TYPE_2:
                viewHolder2 = (ViewHolder2) convertView.getTag();
                break;
        }
    }

    ...
    
    return convertView;
}

这样看起来好像是没什么问题，但运行起来就会崩溃：

FATAL EXCEPTION: main
Process: com.lc.learndemo, PID: 2374
java.lang.ArrayIndexOutOfBoundsException: length=2; index=2
at android.widget.AbsListView$RecycleBin.addScrapView(AbsListView.java:6643)
at android.widget.ListView.measureHeightOfChildren(ListView.java:1292)
at android.widget.ListView.onMeasure(ListView.java:1188)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
at android.widget.LinearLayout.measureHorizontal(LinearLayout.java:1112)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:632)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at com.android.internal.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:446)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at com.android.internal.policy.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2643)
at android.view.View.measure(View.java:18788)
at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2100)
at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1216)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1452)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1107)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6013)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:858)
at android.view.Choreographer.doCallbacks(Choreographer.java:670)
at android.view.Choreographer.doFrame(Choreographer.java:606)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:844)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

问题分析

报错原因是数组越界，但我只传入了一个简单的List，不会有问题，其他地方也没用到数组啊。

其实仔细分析报错信息，可以知道ListView item在布局过程中运行报错，这就怀疑ItemType是否有问题了。最后锁定到 TYPE_1和TYPE_2，当时以为这只是不同类型布局的一个标识，随便取一个值就可以了，谁知问题恰巧就出在这里。

问题定位

跟踪getItemViewType源码可以看到：

/**
 * Get the type of View that will be created by {@link #getView} for the specified item.
 * 
 * @param position The position of the item within the adapter's data set whose view type we
 *        want.
 * @return An integer representing the type of View. Two views should share the same type if one
 *         can be converted to the other in {@link #getView}. Note: Integers must be in the
 *         range 0 to {@link #getViewTypeCount} - 1. {@link #IGNORE_ITEM_VIEW_TYPE} can
 *         also be returned.
 * @see #IGNORE_ITEM_VIEW_TYPE
 */
int getItemViewType(int position);

其中有这样一句：

Note: Integers must be in the range 0 to {@link #getViewTypeCount} - 1.

返回值只能在 0 ~ (getViewTypeCount - 1) 之间

而我的Demo中Item TYPE却是从1开始的，这样，问题就定位到了，接下来就是解决了。

问题解决

如下，Item type 从 0 开始即可：

private final int TYPE_COUNT = 2;
private final int TYPE_1 = 0;
private final int TYPE_2 = 1;

总结

源码是最好的学习资源，遇到类似无厘头Bug，从源码中总能找到答案。