一、问题描述
最近APP进行大改版，整体UI风格都改变了。因此全部包含Banner的界面都需要调整 UI。 在替换过程中，有一个界面的UI出现了问题。
- UI设计人员要求的实现效果
- 实现出现问题的效果
绿色的背景完全显示不出来，导致界面及其难看。
整个Banner控件高度和banner图片资源的高度一样，完全没有背景的空间。
二、分析问题
2.1 使用Layout Inspector 工具分析问题
- 错误的
使用Layout Inspector 工具，看看发现这个背景的高度是1px
- 正常的
使用Layout Inspector 工具，看解决问题之后正常显示的UI 背景高度是585px
- watchset_authorize_head_view.xml 布局文件
可以看出来，预览的布局文件是对的，没有问题的。
而且除了这一个界面不对之外，其他的20多个界面的Banner都是类似的代码，完全没有问题。 因此我怀疑完全不是xml布局导致的问题，而是业务代码添加这个 watchset_authorize_head_view.xml 布局文件出现了问题。
2.2 分析业务代码加载 watchset_authorize_head_view.xml 布局文件的问题
- 错误的加载方式
View headView = View.inflate(this, R.layout.watchset_authorize_head_view, null);
listView.addHeaderView(headView, null, false);
2.3 修复问题
将上面的代码改成下面的加载方式，即可修复该问题。
View headView = LayoutInflater.from(this)
.inflate(R.layout.watchset_authorize_head_view, listView,false);
listView.addHeaderView(headView, null, false);
2.4 解析android.view.LayoutInflater#inflate(int, android.view.ViewGroup)
上面的android.view.View#inflate(Context context, @LayoutRes int resource, ViewGroup root) 方法
最终还是调用了android.view.LayoutInflater#inflate(@LayoutRes int resource, @Nullable ViewGroup root) 方法，如下所示
/**
* Inflate a view from an XML resource. This convenience method wraps the {@link
* LayoutInflater} class, which provides a full range of options for view inflation.
*
* @param context The Context object for your activity or application.
* @param resource The resource ID to inflate
* @param root A view group that will be the parent. Used to properly inflate the
* layout_* parameters.
* @see LayoutInflater
*/
public static View inflate(Context context, @LayoutRes int resource, ViewGroup root) {
LayoutInflater factory = LayoutInflater.from(context);
return factory.inflate(resource, root);
}
android.view.LayoutInflater#inflate(@LayoutRes int resource, @Nullable ViewGroup root) 方法的源代码如下所示
/**
* Inflate a new view hierarchy from the specified xml resource. Throws
* {@link InflateException} if there is an error.
*
* @param resource ID for an XML layout resource to load (e.g.,
* <code>R.layout.main_page</code>)
* @param root Optional view to be the parent of the generated hierarchy.
* @return The root View of the inflated hierarchy. If root was supplied,
* this is the root View; otherwise it is the root of the inflated
* XML file.
*/
public View inflate(@LayoutRes int resource, @Nullable ViewGroup root) {
return inflate(resource, root, root != null);
}
继续调用 android.view.LayoutInflater#inflate(int, android.view.ViewGroup, boolean) 方法
/**
* Inflate a new view hierarchy from the specified xml resource. Throws
* {@link InflateException} if there is an error.
*
* @param resource ID for an XML layout resource to load (e.g.,
* <code>R.layout.main_page</code>)
* @param root Optional view to be the parent of the generated hierarchy (if
* <em>attachToRoot</em> is true), or else simply an object that
* provides a set of LayoutParams values for root of the returned
* hierarchy (if <em>attachToRoot</em> is false.)
* @param attachToRoot Whether the inflated hierarchy should be attached to
* the root parameter? If false, root is only used to create the
* correct subclass of LayoutParams for the root view in the XML.
* @return The root View of the inflated hierarchy. If root was supplied and
* attachToRoot is true, this is root; otherwise it is the root of
* the inflated XML file.
*/
public View inflate(@LayoutRes int resource, @Nullable ViewGroup root, boolean attachToRoot) {
final Resources res = getContext().getResources();
if (DEBUG) {
Log.d(TAG, "INFLATING from resource: \"" + res.getResourceName(resource) + "\" ("
+ Integer.toHexString(resource) + ")");
}
final XmlResourceParser parser = res.getLayout(resource);
try {
return inflate(parser, root, attachToRoot);
} finally {
parser.close();
}
}
继续调用 android.view.LayoutInflater#inflate(org.xmlpull.v1.XmlPullParser, android.view.ViewGroup, boolean) 方法
/**
* Inflate a new view hierarchy from the specified XML node. Throws
* {@link InflateException} if there is an error.
* <p>
* <em><strong>Important</strong></em> For performance
* reasons, view inflation relies heavily on pre-processing of XML files
* that is done at build time. Therefore, it is not currently possible to
* use LayoutInflater with an XmlPullParser over a plain XML file at runtime.
*
* @param parser XML dom node containing the description of the view
* hierarchy.
* @param root Optional view to be the parent of the generated hierarchy (if
* <em>attachToRoot</em> is true), or else simply an object that
* provides a set of LayoutParams values for root of the returned
* hierarchy (if <em>attachToRoot</em> is false.)
* @param attachToRoot Whether the inflated hierarchy should be attached to
* the root parameter? If false, root is only used to create the
* correct subclass of LayoutParams for the root view in the XML.
* @return The root View of the inflated hierarchy. If root was supplied and
* attachToRoot is true, this is root; otherwise it is the root of
* the inflated XML file.
*/
public View inflate(XmlPullParser parser, @Nullable ViewGroup root, boolean attachToRoot) {
synchronized (mConstructorArgs) {
Trace.traceBegin(Trace.TRACE_TAG_VIEW, "inflate");
final Context inflaterContext = mContext;
final AttributeSet attrs = Xml.asAttributeSet(parser);
Context lastContext = (Context) mConstructorArgs[0];
mConstructorArgs[0] = inflaterContext;
//定义返回值，初始化为传入的形参root
View result = root;
try {
// Look for the root node.
int type;
while ((type = parser.next()) != XmlPullParser.START_TAG &&
type != XmlPullParser.END_DOCUMENT) {
// Empty
}
//如果一开始就是END_DOCUMENT，那说明xml文件有问题
if (type != XmlPullParser.START_TAG) {
throw new InflateException(parser.getPositionDescription()
+ ": No start tag found!");
}
//有了上面判断说明这里type一定是START_TAG，也就是xml文件里的root node
final String name = parser.getName();
if (DEBUG) {
System.out.println("**************************");
System.out.println("Creating root view: "
+ name);
System.out.println("**************************");
}
//处理merge tag的情况（merge，你懂的，APP的xml性能优化）
//root必须非空且attachToRoot为true，否则抛异常结束（APP使用merge时要注意的地方，
//因为merge的xml并不代表某个具体的view，只是将它包起来的其他xml的内容加到某个上层ViewGroup中。
if (TAG_MERGE.equals(name)) {
if (root == null || !attachToRoot) {
throw new InflateException("<merge /> can be used only with a valid "
+ "ViewGroup root and attachToRoot=true");
}
//递归inflate方法调运
rInflate(parser, root, inflaterContext, attrs, false);
} else {
// Temp is the root view that was found in the xml
//xml文件中的root view，根据tag节点创建view对象
final View temp = createViewFromTag(root, name, inflaterContext, attrs);
ViewGroup.LayoutParams params = null;
if (root != null) {
if (DEBUG) {
System.out.println("Creating params from root: " +
root);
}
// Create layout params that match root, if supplied
//根据root生成合适的LayoutParams实例
params = root.generateLayoutParams(attrs);
if (!attachToRoot) {
// Set the layout params for temp if we are not
// attaching. (If we are, we use addView, below)
//如果attachToRoot=false就调用view的setLayoutParams方法
temp.setLayoutParams(params);
}
}
if (DEBUG) {
System.out.println("-----> start inflating children");
}
// Inflate all children under temp against its context.
//递归inflate剩下的children
rInflateChildren(parser, temp, attrs, true);
if (DEBUG) {
System.out.println("-----> done inflating children");
}
// We are supposed to attach all the views we found (int temp)
// to root. Do that now.
if (root != null && attachToRoot) {
//root非空且attachToRoot=true则将xml文件的root view加到形参提供的root里
root.addView(temp, params);
}
// Decide whether to return the root that was passed in or the
// top view found in xml.
if (root == null || !attachToRoot) {
//返回xml里解析的root view
result = temp;
}
}
} catch (XmlPullParserException e) {
final InflateException ie = new InflateException(e.getMessage(), e);
ie.setStackTrace(EMPTY_STACK_TRACE);
throw ie;
} catch (Exception e) {
final InflateException ie = new InflateException(parser.getPositionDescription()
+ ": " + e.getMessage(), e);
ie.setStackTrace(EMPTY_STACK_TRACE);
throw ie;
} finally {
// Don't retain static reference on context.
mConstructorArgs[0] = lastContext;
mConstructorArgs[1] = null;
Trace.traceEnd(Trace.TRACE_TAG_VIEW);
}
//返回参数root或xml文件里的root view
return result;
}
}
从上面的源码分析我们可以看出inflate方法的参数含义：
-
inflate(xmlId, null); 只创建temp的View，然后直接返回temp。
-
inflate(xmlId, parent); 创建temp的View，然后执行root.addView(temp, params);最后返回root。
-
inflate(xmlId, parent, false); 创建temp的View，然后执行temp.setLayoutParams(params);然后再返回temp。
-
inflate(xmlId, parent, true); 创建temp的View，然后执行root.addView(temp, params);最后返回root。
-
inflate(xmlId, null, false); 只创建temp的View，然后直接返回temp。
-
inflate(xmlId, null, true); 只创建temp的View，然后直接返回temp。
上面的
android.view.LayoutInflater#inflate(org.xmlpull.v1.XmlPullParser, android.view.ViewGroup, boolean)
方法调用了
android.view.LayoutInflater#rInflate(XmlPullParser parser, View parent, Context context, AttributeSet attrs, boolean finishInflate) 方法
android.view.LayoutInflater#rInflate(XmlPullParser parser, View parent, Context context, AttributeSet attrs, boolean finishInflate)的代码如下所示
/**
* Recursive method used to descend down the xml hierarchy and instantiate
* views, instantiate their children, and then call onFinishInflate().
* <p>
* <strong>Note:</strong> Default visibility so the BridgeInflater can
* override it.
*/
void rInflate(XmlPullParser parser, View parent, final AttributeSet attrs,
boolean finishInflate, boolean inheritContext) throws XmlPullParserException,
IOException {
final int depth = parser.getDepth();
int type;
//XmlPullParser解析器的标准解析模式
while (((type = parser.next()) != XmlPullParser.END_TAG ||
parser.getDepth() > depth) && type != XmlPullParser.END_DOCUMENT) {
//找到START_TAG节点程序才继续执行这个判断语句之后的逻辑
if (type != XmlPullParser.START_TAG) {
continue;
}
//获取Name标记
final String name = parser.getName();
//处理REQUEST_FOCUS的标记
if (TAG_REQUEST_FOCUS.equals(name)) {
parseRequestFocus(parser, parent);
} else if (TAG_TAG.equals(name)) {
//处理tag标记
parseViewTag(parser, parent, attrs);
} else if (TAG_INCLUDE.equals(name)) {
//处理include标记
if (parser.getDepth() == 0) {
//include节点如果是根节点就抛异常
throw new InflateException("<include /> cannot be the root element");
}
parseInclude(parser, parent, attrs, inheritContext);
} else if (TAG_MERGE.equals(name)) {
//merge节点必须是xml文件里的根节点（这里不该再出现merge节点）
throw new InflateException("<merge /> must be the root element");
} else {
//其他自定义节点
final View view = createViewFromTag(parent, name, attrs, inheritContext);
final ViewGroup viewGroup = (ViewGroup) parent;
final ViewGroup.LayoutParams params = viewGroup.generateLayoutParams(attrs);
rInflate(parser, view, attrs, true, true);
viewGroup.addView(view, params);
}
}
//parent的所有子节点都inflate完毕的时候回onFinishInflate方法
if (finishInflate) parent.onFinishInflate();
}
2.5 错误原因
所以会出现上面的异常显示的原因是：
-
inflate(xmlId, null)不能正确处理我们设置的宽和高是因为layout_width，layout_height是相对了父级设置的，而此temp的getLayoutParams为null。
-
inflate(xmlId, parent)能正确显示我们设置的宽高是因为我们的View在设置setLayoutParams时params = root.generateLayoutParams(attrs)不为空。
-
inflate(xmlId, parent,false ) 可以正确处理，因为temp.setLayoutParams(params);这个params正是root.generateLayoutParams(attrs);得到的。
-
inflate(xmlId, null, true)与inflate(xmlId, null, false)不能正确处理我们设置的宽和高是因为layout_width，layout_height是相对了父级设置的，而此temp的getLayoutParams为null。
- 错误代码
View headView = View.inflate(this, R.layout.watchset_authorize_head_view, null);
listView.addHeaderView(headView, null, false);
调用了
android.view.LayoutInflater#inflate(int, android.view.ViewGroup)方法
并且root为空，所以不能正确处理我们设置的宽和高是因为layout_width，layout_height是相对了父级设置的，而此temp的getLayoutParams为null。
因此整个自定义的Banner，除了那种图片是可以显示之外，背景和Banner View的高度完全靠那张图片撑着。
- 正确代码
View headView = LayoutInflater.from(this)
.inflate(R.layout.watchset_authorize_head_view, listView,false);
listView.addHeaderView(headView, null, false);
改成正确代码之后，调用的是inflate(xmlId, parent,false ) 可以正确处理，因为temp.setLayoutParams(params);这个params正是root.generateLayoutParams(attrs);得到的。
所以可以将整个Banner的高度显示出来。
- 为什么之前的Banner UI风格可以正常显示呢？
因为这代码之前的整个Banner是靠三张图片叠起来的，背景图也是png图片正好有高度撑起来了。而改版之后的Banner，只有一个内容是png图片，背景图都是使用shape图来实现的，所以不使用正确的inflate方法的话，就撑不起来。
三、参考链接
更多详细讲解可以参考下面的链接，了解更多关于android.view.LayoutInflater#inflate()方法的分析，当然最好的还是自己看懂源代码。
- https://blog.csdn.net/yanbober/article/details/45970721
- https://blog.csdn.net/u012702547/article/details/52628453
- https://www.cnblogs.com/ganchuanpu/p/6533569.html
- https://blog.csdn.net/lmj623565791/article/details/38171465
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