Android中LayoutInflater類的inflate方法的使用及注意事項

轉自：http://www.ithao123.cn/content-10951307.html

我們在講一個定義好的佈局文件（xml）文件加載到界面上展現出來的時候，通常會用到LayoutInflater的inflate方法，細心的同學會發現這個方法有四種重載，分別是：

public View inflate(@LayoutRes int resource, @Nullable ViewGroup root)；

public View inflate(XmlPullParser parser, @Nullable ViewGroup root)；

public View inflate(@LayoutRes int resource, @Nullable ViewGroup root, boolean attachToRoot)；

public View inflate(XmlPullParser parser, @Nullable ViewGroup root, boolean attachToRoot)；

下面是Android Studio下查看到的源碼即相關方法的參數說明：

/**
* 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);
}
/**
* Inflate a new view hierarchy from the specified xml node. Throws
* {@link InflateException} if there is an error. *
* 
* Important 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.
* @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(XmlPullParser parser, @Nullable ViewGroup root) {
return inflate(parser, root, root != null);
}
/**
* 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
* attachToRoot is true), or else simply an object that
* provides a set of LayoutParams values for root of the returned
* hierarchy (if attachToRoot 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();
}
}
/**
* Inflate a new view hierarchy from the specified XML node. Throws
* {@link InflateException} if there is an error.
* 
* Important 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
* attachToRoot is true), or else simply an object that
* provides a set of LayoutParams values for root of the returned
* hierarchy (if attachToRoot 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;
View result = root;
try {
// Look for the root node.
int type;
while ((type = parser.next()) != XmlPullParser.START_TAG &&
type != XmlPullParser.END_DOCUMENT) {
// Empty
}
if (type != XmlPullParser.START_TAG) {
throw new InflateException(parser.getPositionDescription()
+ ": No start tag found!");
}
final String name = parser.getName();
if (DEBUG) {
System.out.println("**************************");
System.out.println("Creating root view: "
+ name);
System.out.println("**************************");
}
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");
}
rInflate(parser, root, inflaterContext, attrs, false);
} else {
// Temp is the root view that was found in the xml
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
params = root.generateLayoutParams(attrs);
if (!attachToRoot) {
// Set the layout params for temp if we are not
// attaching. (If we are, we use addView, below)
temp.setLayoutParams(params);
}
}
if (DEBUG) {
System.out.println("-----> start inflating children");
}
// Inflate all children under temp against its context.
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.addView(temp, params);
}
// Decide whether to return the root that was passed in or the
// top view found in xml.
if (root == null || !attachToRoot) {
result = temp;
}
}
} catch (XmlPullParserException e) {
InflateException ex = new InflateException(e.getMessage());
ex.initCause(e);
throw ex;
} catch (Exception e) {
InflateException ex = new InflateException(
parser.getPositionDescription()
+ ": " + e.getMessage());
ex.initCause(e);
throw ex;
} finally {
// Don't retain static reference on context.
mConstructorArgs[0] = lastContext;
mConstructorArgs[1] = null;
}
Trace.traceEnd(Trace.TRACE_TAG_VIEW);
return result;
}
}

根據以上源碼我們會發現，重載的四個方法歸根結底最後調用的都是這個方法：

public View inflate(XmlPullParser parser, @Nullable ViewGroup root, boolean attachToRoot)

該方法和以下方法的區別在於下面的方法根據提供的resource來獲得相應的parser，然後再調用上面的方法。

 public View inflate(@LayoutRes int resource, @Nullable ViewGroup root, boolean attachToRoot)

所以我們主要來分析這個方法。參數詳解：

第一個參數：int resource，表示需要加載佈局文件的id，意思是需要將這個佈局文件中加載到Activity中來操作；

第二個參數：ViewGroup root，表示需要附加到resource資源文件的根控件。說明：調用inflate方法後會得到一個View對象，root參數就是接收該 View對象的容器；

第三個參數：boolean attachToRoot，表示是否把inflate得到的View對象添加到root中，該參數爲false時，表示不直接添加到root中；該參數爲true時，表示直接添加到root中；

下面同過具體代碼來說明：

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical">
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="@string/hello" />
<FrameLayout
android:id="@+id/fl_container"
android:layout_width="match_parent"
android:layout_height="wrap_content">
</FrameLayout>
</LinearLayout>

inflate_view_layout.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<CheckBox
android:id="@+id/checkBox1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/checkBox" />
</LinearLayout>

MainActivity.java

package com.rainmonth.inflatemethoddemo;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.text.Layout;
import android.view.LayoutInflater;
import android.view.View;
import android.widget.FrameLayout;
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
FrameLayout frameLayout = (FrameLayout) findViewById(R.id.fl_container);
// 第三個參數設置爲false
View inflateView = LayoutInflater.from(this).inflate(R.layout.inflate_view_layout, frameLayout, false);
// 第三個參數設置爲true，默認爲true
// View inflateView = LayoutInflater.from(this).inflate(R.layout.inflate_view_layout, frameLayout, true);
}
}

第三個參數爲false時的運行結果如下：

此時，inflateView 對應的佈局內容並未呈現出來。

第三個參數爲true時的運行結果如下：

此時inflateView對應的佈局內容呈現出來了。由此可見第三個參數的作用就是是否把inflate出來的參數加入到root容器中，false時不添加；true時添加。

爲了驗證結論，我們在第三個參數爲false時在添加一下代碼：

frameLayout.addView(inflateView);

我們發現其現實結果同第三個參數設置爲true時是一樣的，所以我們的結論得到了驗證。

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