摘要：好處官方對的解析一個不可見大小為的試圖下面會分析這兩點(diǎn)實(shí)現(xiàn)好處顯示優(yōu)酷視頻加載評論列表的，當(dāng)沒有數(shù)據(jù)或者網(wǎng)絡(luò)加載失敗時，如果空列表的會占用資源當(dāng)有數(shù)據(jù)時，才會列表的，延遲加載了布局使用步驟文件每一個必須有屬性，其中的值就是被的的可以通過這

ViewStub is a lightweight view with no dimension that doesn’t draw anything or participate in the layout. it"s an invisible, zero-sized View that can be used to lazily inflate layout resources at runtime.

Android官方對ViewStub的解析:1.ViewStub一個不可見2.大小為0的試圖. (下面會分析這兩點(diǎn)實(shí)現(xiàn))

ViewStub好處：顯示優(yōu)酷視頻加載評論列表的ListView，當(dāng)沒有數(shù)據(jù)或者網(wǎng)絡(luò)加載失敗時，如果inflate空列表的ListView會占用資源；當(dāng)有數(shù)據(jù)時，才會inflate列表的ListView，延遲加載了布局.

 
        
stub_list.xml文件

每一個ViewStub必須有android:layout屬性，其中android:inflatedId的值就是被inflate的View的ID.

findViewById(R.id.list_stub)).setVisibility(View.VISIBLE);
// or
ListView listView = (ListView)((ViewStub) findViewById(R.id.list_stub)).inflate();

可以通過這兩種方式inflate布局，第二種方式inflate布局不需要findViewById()找ListView.查看源碼發(fā)現(xiàn)，可以通過設(shè)置setOnInflateListener()回調(diào)監(jiān)聽獲取inflate的View.

public ViewStub(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
        super(context);

        final TypedArray a = context.obtainStyledAttributes(attrs,
                R.styleable.ViewStub, defStyleAttr, defStyleRes);
        // 解析android:inflatedId屬性，其值是被inflate的View的ID
        mInflatedId = a.getResourceId(R.styleable.ViewStub_inflatedId, NO_ID);
        // 解析android:layout屬性，其值是被inflate的View布局
        mLayoutResource = a.getResourceId(R.styleable.ViewStub_layout, 0);
        // 解析android:id屬性，可以通過findViewByID找到該ViewStub
        mID = a.getResourceId(R.styleable.ViewStub_id, NO_ID);
        a.recycle();
        // 最重要的兩點(diǎn)
        setVisibility(GONE); // 設(shè)置不可見
        setWillNotDraw(true); // 本View不會調(diào)用onDraw()方法繪制內(nèi)容
    }

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    // 設(shè)置試圖大小為0
    setMeasuredDimension(0, 0);
}

 public void setVisibility(int visibility) {
        if (mInflatedViewRef != null) {
            // 已經(jīng)inflate()已經(jīng)調(diào)用，直接獲取該inflate的View控制可見性
            View view = mInflatedViewRef.get();
            if (view != null) {
                view.setVisibility(visibility);
            } else {
                throw new IllegalStateException("setVisibility called on un-referenced view");
            }
        } else {
            // 如果沒有調(diào)用過inflate()方法，并且設(shè)置了試圖可見，就會調(diào)用inflate()加載布局
            super.setVisibility(visibility);
            if (visibility == VISIBLE || visibility == INVISIBLE) {
                inflate();
            }
        }
    }

public View inflate() {
        final ViewParent viewParent = getParent();

        if (viewParent != null && viewParent instanceof ViewGroup) {
            if (mLayoutResource != 0) {
                final ViewGroup parent = (ViewGroup) viewParent;
                final LayoutInflater factory;
                if (mInflater != null) {
                    factory = mInflater;
                } else {
                    factory = LayoutInflater.from(mContext);
                }
                // 加載真正的去加載布局試圖
                final View view = factory.inflate(mLayoutResource, parent,
                        false);
                // 設(shè)置mInflatedId給inflate的View
                if (mInflatedId != NO_ID) {
                    view.setId(mInflatedId);
                }

                // 獲取ViewStub在視圖中的位置
                final int index = parent.indexOfChild(this);
                // 從視圖移除ViewStub
                parent.removeViewInLayout(this);

                final ViewGroup.LayoutParams layoutParams = getLayoutParams();
                // 將inflate的試圖加載父布局中，位置是被移除的ViewStub位置(也就是該ViewStub被替換成layoutView)
                if (layoutParams != null) {
                    parent.addView(view, index, layoutParams);
                } else {
                    parent.addView(view, index);
                }

                mInflatedViewRef = new WeakReference(view);
                // 試圖加載完成回調(diào)
                if (mInflateListener != null) {
                    mInflateListener.onInflate(this, view);
                }

                return view;
            } else {
                throw new IllegalArgumentException("ViewStub must have a valid layoutResource");
            }
        } else {
            throw new IllegalStateException("ViewStub must have a non-null ViewGroup viewParent");
        }

}

// 設(shè)置回調(diào)監(jiān)聽
public void setOnInflateListener(OnInflateListener inflateListener) {
        mInflateListener = inflateListener;
    }

public static interface OnInflateListener {
     // inflated：被inflate的View
    void onInflate(ViewStub stub, View inflated);
}

一旦調(diào)用setVisibility(View.VISIBLE)或者inflate()方法之后，該ViewStub將會從試圖中被移除（此時調(diào)用findViewById()是找不到該ViewStub對象).

如果指定了mInflatedId , 被inflate的layoutView的id就是mInflatedId.

被inflate的layoutView的layoutParams與ViewStub的layoutParams相同.

以上三點(diǎn)注意的事項(xiàng)可以從源碼中得知:

 //注意事項(xiàng)第二點(diǎn)
if (mInflatedId != NO_ID) {
    view.setId(mInflatedId);
}
//注意事項(xiàng)第一點(diǎn)
final int index = parent.indexOfChild(this);
parent.removeViewInLayout(this);

final ViewGroup.LayoutParams layoutParams = getLayoutParams();
if (layoutParams != null) {
     //注意事項(xiàng)第三點(diǎn)
    parent.addView(view, index, layoutParams);
} else {
    parent.addView(view, index);
}