View标签与view标签引发的bug思考

题引：前些天想用View标签写个下划线，结果把View写成view了，出现了一个奇葩的bug。

一、bug堆栈

03-09 15:35:28.654 29199-29199/com.jiudaifu.yangsheng E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.jiudaifu.yangsheng, PID: 29199
**java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.equals(java.lang.Object)' on a null object reference** at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:734)
at android.view.LayoutInflater.rInflate(LayoutInflater.java:825)
at android.view.LayoutInflater.rInflate(LayoutInflater.java:828)
at android.view.LayoutInflater.inflate(LayoutInflater.java:523)
at android.view.LayoutInflater.inflate(LayoutInflater.java:425)
at android.view.LayoutInflater.inflate(LayoutInflater.java:368)
at com.jiudaifu.yangsheng.adapter.CaseListAdapter.getView(CaseListAdapter.java:51)
at android.widget.AbsListView.obtainView(AbsListView.java:2369)
at android.widget.ListView.measureHeightOfChildren(ListView.java:1274)
at android.widget.ListView.onMeasure(ListView.java:1186)
at android.view.View.measure(View.java:17628)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5548)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1467)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:747)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:638)
at android.view.View.measure(View.java:17628)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5548)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:436)
at android.view.View.measure(View.java:17628)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5548)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1467)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:747)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:638)
at android.view.View.measure(View.java:17628)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5548)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1467)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:747)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:638)
at android.view.View.measure(View.java:17628)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5548)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:436)
at android.view.View.measure(View.java:17628)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5548)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1467)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:747)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:638)
at android.view.View.measure(View.java:17628)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5548)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:436)
at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2639)
at android.view.View.measure(View.java:17628)
at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2081)
at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1217)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1423)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1105)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6204)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:799)
at android.view.Choreographer.doCallbacks(Choreographer.java:612)
at android.view.Choreographer.doFrame(Choreographer.java:581)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:785)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5669)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:960)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)
03-09 15:35:28.964 29199-29199/com.jiudaifu.yangsheng I/Process: Sending signal. PID: 29199 SIG: 9

二、bug分析

涉及的Android源码如下：

View createViewFromTag(View parent, String name, Context context, AttributeSet attrs,
boolean ignoreThemeAttr) {
if (name.equals("view")) {
name = attrs.getAttributeValue(null, "class");
}

// Apply a theme wrapper, if allowed and one is specified.
if (!ignoreThemeAttr) {
final TypedArray ta = context.obtainStyledAttributes(attrs, ATTRS_THEME);
final int themeResId = ta.getResourceId(0, 0);
if (themeResId != 0) {
context = new ContextThemeWrapper(context, themeResId);
}
ta.recycle();
}

if (name.equals(TAG_1995)) {
// Let's party like it's 1995!
return new BlinkLayout(context, attrs);
}

try {
View view;
if (mFactory2 != null) {
view = mFactory2.onCreateView(parent, name, context, attrs);
} else if (mFactory != null) {
view = mFactory.onCreateView(name, context, attrs);
} else {
view = null;
}

if (view == null && mPrivateFactory != null) {
view = mPrivateFactory.onCreateView(parent, name, context, attrs);
}

if (view == null) {
final Object lastContext = mConstructorArgs[0];
mConstructorArgs[0] = context;
try {
if (-1 == name.indexOf('.')) {
view = onCreateView(parent, name, attrs);
} else {
view = createView(name, null, attrs);
}
} finally {
mConstructorArgs[0] = lastContext;
}
}

return view;
} catch (InflateException e) {
throw e;

} catch (ClassNotFoundException e) {
final InflateException ie = new InflateException(attrs.getPositionDescription()
+ ": Error inflating class " + name);
ie.initCause(e);
throw ie;

} catch (Exception e) {
final InflateException ie = new InflateException(attrs.getPositionDescription()
+ ": Error inflating class " + name);
ie.initCause(e);
throw ie;
}
}

三、Android源码分析

参考：http://blog.csdn.net/gorgle/article/details/51428515