动态计算listview的高度listItem.measure(0, 0)报空指针异常解决办法-CFANZ编程社区

当我们在使用Listview这类的控件和scrollview嵌套使用的时候会调用一个动态计算listview高度的方法。网上大部分方法基本都如下：

[java] view plain copy

1. public class Utils {  
2. public static void setListViewHeightBasedOnChildren(ListView listView) {  
3.             ListAdapter listAdapter = listView.getAdapter();   
4. if (listAdapter == null) {  
5. // pre-condition  
6. return;  
7.             }  
8.   
9. int totalHeight = 0;  
10. for (int i = 0; i < listAdapter.getCount(); i++) {  
11. null, listView);  
12. 0, 0);  
13.                 totalHeight += listItem.getMeasuredHeight();  
14.             }  
15.   
16.             ViewGroup.LayoutParams params = listView.getLayoutParams();  
17. 1));  
18.             listView.setLayoutParams(params);  
19.         }  
20.     }

但是有时候我们会发现每次调用的时候都会产生在listItem.measure(0,0)报空指针异常。但是你去debug会发现listItem 并不是为空，那么为啥会报错呢。你去看你的item的布局会发现肯定不是LinearLayout，这个时候把它换为LinearLayout 就好了。网上的说法是原来是 Linearlayout重写了onmeasure方法，其他的布局文件没有重写onmeasure,所以在调用listItem.measure(0, 0); 会报空指针异常，如果想用这个东东，就必须用linearlayout布局。但是我看源码发现其实并不能这样说，其他布局也是重写了onmeasure方法的，不过谷歌有特别备注说明:

[java] view plain copy

1. // We need to know our size for doing the correct computation of children positioning in RTL  
2. // mode but there is no practical way to get it instead of running the code below.  
3. // So, instead of running the code twice, we just set the width to a "default display width"  
4. // before the computation and then, as a last pass, we will update their real position with  
5. // an offset equals to "DEFAULT_WIDTH - width".

大伙去翻译翻译看看啥意思。而且这种情况并不是在所有的手机上会出现，现在很多手机厂商有修改rom。我只是在华为的一款手机上报了这个错。基于这些我写了一个稳妥一点的计算方法：

[java] view plain copy

1. public class Utils {  
2. public static void setListViewHeightBasedOnChildren(ListView listView) {  
3.              
4. ListAdapter listAdapter = listView.getRefreshableView().getAdapter();  
5. if (listAdapter == null) {  
6. return;  
7. }  
8.   
9. int totalHeight = 0;  
10.   
11. for (int i = 0; i < listAdapter.getCount(); i++) {  
12.   
13. null, listView);  
14. if (listItem == null) continue;  
15.   
16. if (listItem instanceof LinearLayout){  
17. 0, 0);  
18.         totalHeight += listItem.getMeasuredHeight();  
19. else {  
20. try {  
21. 0, 0);  
22.             totalHeight += listItem.getMeasuredHeight();  
23. catch (NullPointerException e){  
24. 80);//这里自己随便写个大小做容错处理吧  
25. "bobge","NullPointerException");  
26.         }  
27.     }  
28.   
29.     totalHeight += listItem.getMeasuredHeight();  
30.   
31. }  
32.   
33. ViewGroup.LayoutParams params = listView.getLayoutParams();  
34.   
35. params.height = totalHeight  
36. 1));  
37.   
38.   
39. listView.setLayoutParams(params);  
40.   
41.         }  
42.     }