文章标题

介绍

ViewStub 是一个轻量级的View，没有尺寸，不绘制任何东西，因此绘制或者移除时更省时。(ViewStub不可见，大小为0)

优点

实现View的延迟加载，避免资源的浪费，减少渲染时间，在需要的时候才加载View

缺点

ViewStub所要替代的layout文件中不能有<merge>标签
ViewStub在加载完后会被移除，或者说是被加载进来的layout替换掉了
用法

<ViewStub    android:id="@+id/stub_import"    android:inflatedId="@+id/panel_import"    android:layout="@layout/progress_overlay"    android:layout_width="fill_parent"    android:layout_height="wrap_content"    android:layout_gravity="bottom" />

用ViewStub加载layout文件时，可以调用 setVisibility(View.VISIBLE) 或者 inflate()

((ViewStub) findViewById(R.id.stub_import)).setVisibility(View.VISIBLE);// orView importPanel = ((ViewStub) findViewById(R.id.stub_import)).inflate();

注意

• 一旦ViewStub visible/inflated，则ViewStub将从视图框架中移除，其id stub_import 也会失效
• ViewStub被绘制完成的layout文件取代，并且该layout文件的root view的id是android:inflatedId指定的id panel_import，root view的布局和ViewStub视图的布局保持一致

<!-- layout_viewstub.xml 要延迟加载的view --><?xml version="1.0" encoding="utf-8"?><LinearLayout android:id="@+id/layout_viewstub_old"    xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:orientation="vertical">    <TextView        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_margin="5dp"        android:background="@android:color/darker_gray"        android:padding="5dp"        android:text="This is the layout instead of ViewStub view."/></LinearLayout>

<!-- act_test_viewstub.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:gravity="center_horizontal"    android:orientation="vertical">    <TextView        android:id="@+id/act_test_viewstub_tv_show"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_margin="5dp"        android:background="@android:color/darker_gray"        android:padding="5dp"        android:text="Show ViewStub"/>    <ViewStub        android:id="@+id/act_test_viewstub_viewstub"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:inflatedId="@+id/act_layout_viewstub_new"        android:layout="@layout/layout_viewstub"/>    <!--<include-->        <!--android:layout_width="wrap_content"-->        <!--android:layout_height="wrap_content"-->        <!--layout="@layout/layout_viewstub"/>--></LinearLayout>

public class ViewStubTestActivity extends FragmentActivity {    private static final String TAG = "test_viewstub";    protected ViewStub mViewStub;    @Override    protected void onCreate(@Nullable Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.act_test_viewstub);        mViewStub = (ViewStub) findViewById(R.id.act_test_viewstub_viewstub);        Log.e(TAG, "viewstub: " + findViewById(R.id.act_test_viewstub_viewstub));        Log.e(TAG, "layout: " + findViewById(R.id.act_layout_viewstub_new));        findViewById(R.id.act_test_viewstub_tv_show).setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View v) {                View layoutView;//                mViewStub.setVisibility(View.VISIBLE);                layoutView = mViewStub.inflate();                Log.e(TAG, "mViewStub: " + mViewStub);                // ViewStub在visible/inflated后会被移除，所以此处为null                Log.e(TAG, "viewstub: " + findViewById(R.id.act_test_viewstub_viewstub));//                layoutView = findViewById(R.id.act_layout_viewstub_new);                Log.e(TAG, "layoutView equals finviewbyid(layout): " +                        layoutView.equals(findViewById(R.id.act_layout_viewstub_new)));                Log.e(TAG, "layout: " + layoutView);                if (layoutView != null) {                    // layoutView的root view id 是mViewStub inflatedId指定的ID                    if (layoutView.getId() == R.id.act_layout_viewstub_new) {                        Log.e(TAG, "layout root id is act_layout_viewstub_new");                    } else if (layoutView.getId() == R.id.layout_viewstub_old) {                        Log.e(TAG, "layout root id is layout_viewstub_old");                    } else {                        Log.e(TAG, "layout root id is anyone : " + layoutView.getId());                    }                    // layoutView的root view布局 和mViewStub的布局保持一致                    int width = layoutView.getLayoutParams().width;                    if (width == ViewGroup.LayoutParams.MATCH_PARENT) {                        Log.e(TAG, "layout width is MATCH_PARENT");                    } else if (width == ViewGroup.LayoutParams.WRAP_CONTENT) {                        Log.e(TAG, "layout width is WRAP_CONTENT");                    } else {                        Log.e(TAG, "layout width is anyone : " + width);                    }                }            }        });    }}