layoutinflater详解

layoutinflater

ListView的Adapter的getView方法中基本都会出现，使用inflate方法去加载一个布局，用于ListView的每个Item的布局，但是这三个方法究竟有什么用，还是不是很清楚。

convertView = mInflater.inflate(R.layout.item, null);
convertView = mInflater.inflate(R.layout.item, parent ,false);
convertView = mInflater.inflate(R.layout.item, parent ,true);

于是就动手实践一下

在ListView里面实践一下

  @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ViewHolder holder = null;
        if (convertView == null) {
            holder = new ViewHolder();
//            不能正确的处理长宽高
//            convertView = layoutInflater.inflate(R.layout.item, null);
//            能够正常的处理长宽高
            convertView = layoutInflater.inflate(R.layout.item, parent, false);
//            convertView = layoutInflater.inflate(R.layout.item, parent, true);
            holder.mBtn = (Button) convertView.findViewById(R.id.id_btn);
            convertView.setTag(holder);
        } else {
            holder = (ViewHolder) convertView.getTag();
        }
        holder.mBtn.setText(mData.get(position));
        return convertView;
    }

Item的代码

<?xml version="1.0" encoding="utf-8"?>
<Button xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/id_btn"
    android:layout_width="120dp"
    android:layout_height="120dp">

先尝试第一个

convertView = mInflater.inflate(R.layout.item, null);

效果是这样但是长宽高没有像设置的一样

然后第二个

convertView = mInflater.inflate(R.layout.item, parent ,false);

效果图

可以看出这些按钮都有了具体的长宽高 不同于上面没有具体的边距

最后尝试第三个

convertView = mInflater.inflate(R.layout.item, parent ,true);

然而出现了错误

到这里我就不明白了 于是我看了一下看了一下别人的博客然后推荐我看一下源代码

这里面是源代码

   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;
        }
    }

看到 View result = root; 把root的地址指向给view 最后 return result;可以看出最后返回的是result了

看一下第二个参数的判断

        if (root == null || !attachToRoot) {
                        throw new InflateException("<merge /> can be used only with a valid "
                                + "ViewGroup root and attachToRoot=true");
                    }

可以看出root==null 和 第三个参数为false 抛出异常

 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);
                    }
                }

这里是获取父类的信息

final View temp = createViewFromTag(root, name, inflaterContext, attrs);

root不为null的时候， params = root.generateLayoutParams(attrs);获取父组件的LayoutParams，会把父布局的setLayoutParams设置给唤醒的子类。相对父级设置这就是为什么按钮可以按照参数来设置长宽高.

接下来看一下第三个参数

  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;
                }

从代码中看出attachToRoot为true时可以往父组件上增加View 之后。如果root为null，或者attachToRoot为false则，将temp赋值给result。
最后返回result。

Inflate(resId , null ) 只创建temp ,返回temp

Inflate(resId , parent, false )创建temp，然后执行temp.setLayoutParams(params);返回temp

Inflate(resId , parent, true ) 创建temp，然后执行root.addView(temp, params);最后返回root

错误的原因：

  @Override
    public void addView(View child) {
        throw new UnsupportedOperationException("addView(View) is not supported in AdapterView");
    }

之后我们实践一下在没有在listview的情况下实践这三个方法

public class MainActivity extends Activity {
    private ListView mListView;
    private MyAdapter myAdapter;
    private List<String> mDatas = Arrays.asList("hello","java","android");
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
//        setContentView(R.layout.test_layout);
//        mListView = (ListView) findViewById(R.id.listview);
//        myAdapter = new MyAdapter(this,mDatas);
//        mListView.setAdapter(myAdapter);


        View view1 = LayoutInflater.from(this).inflate(R.layout.item,null);
        View view2 = LayoutInflater.from(this).inflate(R.layout.item,(ViewGroup)findViewById(android.R.id.content),false);
        View view3 = LayoutInflater.from(this).inflate(R.layout.item,(ViewGroup)findViewById(android.R.id.content),true);

        Log.e("TAG", "view1 = " + view1 + " , view1.layoutParams = " + view1.getLayoutParams());
        Log.e("TAG", "view2 = " + view2  +" , view2.layoutParams = " + view2.getLayoutParams());
        Log.e("TAG", "view3 = " + view3  );
}

实践的结果

参考的博客： http://blog.csdn.net/lmj623565791/article/details/38171465