动态加载布局LayoutInflater.inflate()源代码解析

综合技术 简书

如何获取LayoutInflater

获得 LayoutInflater 实例的三种方式

1.LayoutInflater inflater = getLayoutInflater(); //调用Activity的getLayoutInflater()

2.LayoutInflater localinflater =(LayoutInflater)context.getSystemService

(Context.LAYOUT_INFLATER_SERVICE);
  1. LayoutInflater inflater = LayoutInflater.from(context);

本质上都是调用方式二。

LayoutInflater.inflate()源代码分析

1.两个参数的inflate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.,
     *        R.layout.main_page)
     * @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);
    }

第一个参数是加载的xml布局资源,第二个是父布局。里面会调用三个参数的方法。

2.看一下三个参数的方法

/**
     * 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.,
     *        R.layout.main_page)
     * @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();
        }
    }

最终会调用,inflate(parser, root, attachToRoot);方法。

第三个参数attachToRoot是true的时候,会自动加载到第二个参数提到的父布局。

3.inflate(parser, root, attachToRoot);方法分析

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(" 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;
        }
    }

4.总结分析

<1当调用两个参数的时候inflate()

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

如果父布局不为空,那么会默认inflate(XmlPullParser parser, @Nullable ViewGroup root, boolean attachToRoot)第三个参数也是true。

第三个参数的作用如下;

if (root != null && attachToRoot) {
                        root.addView(temp, params);
                    }

第三个参数是空的时候,会自动添加到第二个参数的父布局中。

<2 第二个参数的作用

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);
                        }
                    }

当只有第二个参数不为空时候,view的layoutparam才有意义,否则是就是空,那么在xml在设置的高宽,margin就没有意义了,会使用默认的layoutparam,默认的layoutparam的的layout;width和layout:height都是wrap_content。

5.inflate的重载方式

如下四种:

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


 public View inflate(XmlPullParser parser, @Nullable ViewGroup root) {
        return inflate(parser, root, root != null);
    }


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


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

最终都会调用 inflate(XmlPullParser parser, @Nullable ViewGroup root, boolean attachToRoot)方法。

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