介紹

ViewStub 是一個輕量級的View，沒有尺寸置媳，不繪制任何東西于樟，因此繪制或者移除時更省時。(ViewStub不可見拇囊，大小為0)

優(yōu)點

實現(xiàn)View的延遲加載迂曲，避免資源的浪費，減少渲染時間寥袭，在需要的時候才加載View

缺點

• ViewStub所要替代的layout文件中不能有<merge>標簽
• ViewStub在加載完后會被移除路捧，或者說是被加載進來的layout替換掉了

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加載layout文件時，可以調(diào)用 setVisibility(View.VISIBLE) 或者 inflate()

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

注意

• 一旦ViewStub visible/inflated传黄，則ViewStub將從視圖框架中移除鬓长，其id stub_import 也會失效
• ViewStub被繪制完成的layout文件取代，并且該layout文件的root view的id是android:inflatedId指定的id panel_import尝江，root view的布局和ViewStub視圖的布局保持一致

實例

<!-- layout_viewstub.xml 要延遲加載的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后會被移除涉波，所以此處為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);
                    }
                }
            }
        });

    }
}

運行結(jié)果.png