android中LayoutInflater.from(context).inflate的分析

在应用中自定义一个view，需要获取这个view的布局，需要用到

(LinearLayout) LayoutInflater.from(context).inflate(R.layout.contentitem, null);

这个方法。

一般的资料中的第二个参数会是一个null。通常情况下没有问题，但是如果我想给这个view设置一个对应的类，然后通过这个类来操作的话就会出问题。

先看下面的例子

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              android:orientation="vertical"
              android:layout_width="match_parent"
              android:layout_height="match_parent"
              android:background="@color/white">

    <TextView
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:id="@+id/textViewTitle"
            android:textColor="@color/black"
            android:gravity="center" android:textSize="26dp"/>

    <TextView
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:id="@+id/textViewAuthor"
            android:layout_gravity="left" android:textColor="@android:color/darker_gray" android:textSize="16dp"/>

    <ImageView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/imageView"
            android:layout_gravity="center_horizontal"
            android:scaleType="center"/>

    <TextView
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:id="@+id/textViewContent"
            android:layout_gravity="center_horizontal" android:textColor="@color/black" android:textSize="20dp"/>

    <LinearLayout
            android:layout_width="fill_parent"
            android:layout_height="2dp"
            android:layout_gravity="center"
            android:background="@color/black">
    </LinearLayout>

    <TextView
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:id="@+id/textViewOtherInfo"
            android:layout_gravity="left" android:clickable="true" android:textColor="@android:color/darker_gray"
            android:textSize="16dp"/>
</LinearLayout>

对应的类是

public class ContentItemView extends LinearLayout {

    private TextView title;
    private TextView author;
    private TextView content;
    private TextView otherInfo;
    private ImageView contentImage;

    private ContentInfo info;

    public ContentItemView(Context context) {
        super(context);
        init(context);
    }

    private void init(Context context) {
        LinearLayout convertView =
        (LinearLayout) LayoutInflater.from(context).inflate(R.layout.contentitem, null);
        title = (TextView) convertView.findViewById(R.id.textViewTitle);
        author = (TextView) convertView.findViewById(R.id.textViewAuthor);
        content = (TextView) convertView.findViewById(R.id.textViewContent);
        otherInfo = (TextView) convertView.findViewById(R.id.textViewOtherInfo);
        contentImage = (ImageView) convertView.findViewById(R.id.imageView);
    }
}

这个自定义view我想将它添加到一个listview中。

    public void add(final ContentInfo info) {
        ContentItemView contentItemView  = new ContentItemView(context);
        contentItemView.setContentInfo(info);
        contentItemView.setLayoutParams(new AbsListView.LayoutParams(AbsListView.LayoutParams.MATCH_PARENT, AbsListView.LayoutParams.WRAP_CONTENT));

        data.add(contentItemView);
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        return data.get(position);
    }

程序运行起来以后，没有任何问题，但是界面没有显示出来，仅仅是在listview中多了一系列黑色的条条

如果将

(LinearLayout) LayoutInflater.from(context).inflate(R.layout.contentitem, null);

修改为

(LinearLayout) LayoutInflater.from(context).inflate(R.layout.contentitem, this);

显示就会正常

上面的东西很多资料里面都有，但是原因是什么？我在网络上找了很久都没有找到，于是就自己研究了下代码

    public View inflate(int resource, ViewGroup root) {
        return inflate(resource, root, root != null);
    }

    public View inflate(int resource, ViewGroup root, boolean attachToRoot) {
        if (DEBUG) System.out.println("INFLATING from resource: " + resource);
        XmlResourceParser parser = getContext().getResources().getLayout(resource);
        try {
            return inflate(parser, root, attachToRoot);
        } finally {
            parser.close();
        }
    }
    public View inflate(XmlPullParser parser, ViewGroup root, boolean attachToRoot) {
........
                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, attrs, false);
                } else {
                    // Temp is the root view that was found in the xml
                    View temp;
                    if (TAG_1995.equals(name)) {
                        temp = new BlinkLayout(mContext, attrs);
                    } else {
                        temp = createViewFromTag(root, name, 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 (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;
                    }
                }
.....
}

可以看到在inflate(XmlPullParser parser, ViewGroup root, boolean attachToRoot)函数中，只有root不等于空的情况下才能够真正的把view添加到listview中。

看看参数root的含义：@param root Optional view to be the parent of the generated hierarchy 

就是说这个表示的事view的容器是什么。如果不告诉SDK你要把这个view放到哪里，当然就不能生成view了。