Android 如何防止getChildAt（position）.getWidth（）返回null？

我在v4支持库的早期版本中使用了此方法，它工作正常，但当我将其更改为最新版本时，只要position and positionoffset为0，此方法就会返回null，tabsContainer为linearLayout：

  positionOffset * tabsContainer.getChildAt(position).getWidth())

从方法：

 scrollToChild(position, (int) (positionOffset *     
 tabsContainer.getChildAt(position).getWidth()));

我需要一些帮助来避免它返回null，而不使用if position=0，因为它在资源为null时阻止创建选项卡，需要一些帮助吗

 public class PagerSlidingTabStrip extends HorizontalScrollView {

public interface IconTabProvider {
    public int getPageIconResId(int position);
}

// @formatter:off
private static final int[] ATTRS = new int[] {
    android.R.attr.textSize,
    android.R.attr.textColor
 };
// @formatter:on

private LinearLayout.LayoutParams defaultTabLayoutParams;
private LinearLayout.LayoutParams expandedTabLayoutParams;

private final PageListener pageListener = new PageListener();
public OnPageChangeListener delegatePageListener;

private LinearLayout tabsContainer;
private ViewPager pager;

private int tabCount;

private int currentPosition = 0;
private float currentPositionOffset = 0f;

private Paint rectPaint;
private Paint dividerPaint;

private int indicatorColor = 0xFF666666;
private int underlineColor = 0x1A000000;
private int dividerColor = 0x1A000000;

private boolean shouldExpand = false;
private boolean textAllCaps = true;

private int scrollOffset = 52;
private int indicatorHeight = 8;
private int underlineHeight = 2;
private int dividerPadding = 12;
private int tabPadding = 24;
private int dividerWidth = 1;

private int tabTextSize = 12;
private int tabTextColor = 0xFF666666;
private Typeface tabTypeface = null;
private int tabTypefaceStyle = Typeface.BOLD;

private int lastScrollX = 0;

private int tabBackgroundResId = R.drawable.background_tab;

private Locale locale;

public PagerSlidingTabStrip(Context context) {
    this(context, null);
}

public PagerSlidingTabStrip(Context context, AttributeSet attrs) {
    this(context, attrs, 0);
}

public PagerSlidingTabStrip(Context context, AttributeSet attrs, int defStyle) {
    super(context, attrs, defStyle);

    setFillViewport(true);
    setWillNotDraw(false);

    tabsContainer = new LinearLayout(context);
    tabsContainer.setOrientation(LinearLayout.HORIZONTAL);
    tabsContainer.setLayoutParams(new LayoutParams(LayoutParams.MATCH_PARENT, 
 LayoutParams.MATCH_PARENT));
    addView(tabsContainer);

    DisplayMetrics dm = getResources().getDisplayMetrics();

    scrollOffset = (int) 
 TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, scrollOffset, dm);
    indicatorHeight = (int) 
 TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, indicatorHeight, dm);
    underlineHeight = (int) 
 TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, underlineHeight, dm);
    dividerPadding = (int) 
 TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, dividerPadding, dm);
    tabPadding = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 
  tabPadding, dm);
    dividerWidth = (int) 
 TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, dividerWidth, dm);
    tabTextSize = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_SP, 
  tabTextSize, dm);

    // get system attrs (android:textSize and android:textColor)

    TypedArray a = context.obtainStyledAttributes(attrs, ATTRS);

    tabTextSize = a.getDimensionPixelSize(0, tabTextSize);
    tabTextColor = a.getColor(1, tabTextColor);

    a.recycle();

    // get custom attrs

    a = context.obtainStyledAttributes(attrs, 
 R.styleable.PagerSlidingTabStrip);

    indicatorColor = 
 a.getColor(R.styleable.PagerSlidingTabStrip_pstsIndicatorColor, indicatorColor);
    underlineColor = 
 a.getColor(R.styleable.PagerSlidingTabStrip_pstsUnderlineColor, underlineColor);
    dividerColor = 
 a.getColor(R.styleable.PagerSlidingTabStrip_pstsDividerColor, dividerColor);
    indicatorHeight = 
 a.getDimensionPixelSize(R.styleable.PagerSlidingTabStrip_pstsIndicatorHeight, 
 indicatorHeight);
    underlineHeight = 
 a.getDimensionPixelSize(R.styleable.PagerSlidingTabStrip_pstsUnderlineHeight, 
 underlineHeight);
    dividerPadding = 
 a.getDimensionPixelSize(R.styleable.PagerSlidingTabStrip_pstsDividerPadding, 
  dividerPadding);
    tabPadding = 
 a.getDimensionPixelSize(R.styleable.PagerSlidingTabStrip_pstsTabPaddingLeftRight, 
 tabPadding);
    tabBackgroundResId = 
 a.getResourceId(R.styleable.PagerSlidingTabStrip_pstsTabBackground, 
 tabBackgroundResId);
    shouldExpand = 
a.getBoolean(R.styleable.PagerSlidingTabStrip_pstsShouldExpand, shouldExpand);
    scrollOffset = 
  a.getDimensionPixelSize(R.styleable.PagerSlidingTabStrip_pstsScrollOffset,  
 scrollOffset);
    textAllCaps = 
 a.getBoolean(R.styleable.PagerSlidingTabStrip_pstsTextAllCaps, textAllCaps);

    a.recycle();

    rectPaint = new Paint();
    rectPaint.setAntiAlias(true);
    rectPaint.setStyle(Style.FILL);

    dividerPaint = new Paint();
    dividerPaint.setAntiAlias(true);
    dividerPaint.setStrokeWidth(dividerWidth);

    defaultTabLayoutParams = new 
  LinearLayout.LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.MATCH_PARENT);
    expandedTabLayoutParams = new LinearLayout.LayoutParams(0, 
  LayoutParams.MATCH_PARENT, 1.0f);

    if (locale == null) {
        locale = getResources().getConfiguration().locale;
    }
}

public void setViewPager(ViewPager pager) {
    this.pager = pager;

    if (pager.getAdapter() == null) {
        throw new IllegalStateException("ViewPager does not have adapter 
  instance.");
    }

    pager.setOnPageChangeListener(pageListener);

    notifyDataSetChanged();
}

public void setOnPageChangeListener(OnPageChangeListener listener) {
    this.delegatePageListener = listener;
}

public void notifyDataSetChanged() {

    tabsContainer.removeAllViews();

    tabCount = pager.getAdapter().getCount();

    for (int i = 0; i < tabCount; i++) {

        if (pager.getAdapter() instanceof IconTabProvider) {
            addIconTab(i, ((IconTabProvider) 
 pager.getAdapter()).getPageIconResId(i));
        } else {
            addTextTab(i, 
 pager.getAdapter().getPageTitle(i).toString());
        }

    }

    updateTabStyles();

    getViewTreeObserver().addOnGlobalLayoutListener(new 
  OnGlobalLayoutListener() {


        @Override
        public void onGlobalLayout() {

            if (Build.VERSION.SDK_INT < 
 Build.VERSION_CODES.JELLY_BEAN) {

 getViewTreeObserver().removeOnGlobalLayoutListener(this);
            } else {

 getViewTreeObserver().removeOnGlobalLayoutListener(this);
            }

            currentPosition = pager.getCurrentItem();
            scrollToChild(currentPosition, 0);
        }
    });

}

private void addTextTab(final int position, String title) {

    TextView tab = new TextView(getContext());
    tab.setText(title);
    tab.setGravity(Gravity.CENTER);
    tab.setSingleLine();

    addTab(position, tab);
}

private void addIconTab(final int position, int resId) {

    ImageButton tab = new ImageButton(getContext());
    tab.setImageResource(resId);

    addTab(position, tab);

}

private void addTab(final int position, View tab) {
    tab.setFocusable(true);
    tab.setOnClickListener(new OnClickListener() {
        @Override
        public void onClick(View v) {
            pager.setCurrentItem(position);
        }
    });

    tab.setPadding(tabPadding, 0, tabPadding, 0);
    tabsContainer.addView(tab, position, shouldExpand ? 
 expandedTabLayoutParams : defaultTabLayoutParams);
}

private void updateTabStyles() {

    for (int i = 0; i < tabCount; i++) {

        View v = tabsContainer.getChildAt(i);

        v.setBackgroundResource(tabBackgroundResId);

        if (v instanceof TextView) {

            TextView tab = (TextView) v;
            tab.setTextSize(TypedValue.COMPLEX_UNIT_PX, tabTextSize);
            tab.setTypeface(tabTypeface, tabTypefaceStyle);
            tab.setTextColor(tabTextColor);

            // setAllCaps() is only available from API 14, so the 
 upper case is made manually if we are on a
            // pre-ICS-build
            if (textAllCaps) {
                if (Build.VERSION.SDK_INT >= 
 Build.VERSION_CODES.ICE_CREAM_SANDWICH) {
                    tab.setAllCaps(true);
                } else {

 tab.setText(tab.getText().toString().toUpperCase(locale));
                }
            }
        }
    }

}

private void scrollToChild(int position, int offset) {

    if (tabCount == 0) {
        return;
    }

    int newScrollX = tabsContainer.getChildAt(position).getLeft() + offset;

    if (position > 0 || offset > 0) {
        newScrollX -= scrollOffset;
    }

    if (newScrollX != lastScrollX) {
        lastScrollX = newScrollX;
        scrollTo(newScrollX, 0);
    }

}

@Override
protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);

    if (isInEditMode() || tabCount == 0) {
        return;
    }

    final int height = getHeight();

    // draw indicator line

    rectPaint.setColor(indicatorColor);

    // default: line below current tab
    View currentTab = tabsContainer.getChildAt(currentPosition);
    float lineLeft = currentTab.getLeft();
    float lineRight = currentTab.getRight();

    // if there is an offset, start interpolating left and right coordinates  
 between current and next tab
    if (currentPositionOffset > 0f && currentPosition < tabCount - 1) {

        View nextTab = tabsContainer.getChildAt(currentPosition + 1);
        final float nextTabLeft = nextTab.getLeft();
        final float nextTabRight = nextTab.getRight();

        lineLeft = (currentPositionOffset * nextTabLeft + (1f - 
 currentPositionOffset) * lineLeft);
        lineRight = (currentPositionOffset * nextTabRight + (1f - 
 currentPositionOffset) * lineRight);
    }

    canvas.drawRect(lineLeft, height - indicatorHeight, lineRight, height, 
 rectPaint);

    // draw underline

    rectPaint.setColor(underlineColor);
    canvas.drawRect(0, height - underlineHeight, tabsContainer.getWidth(), 
 height, rectPaint);

    // draw divider

    dividerPaint.setColor(dividerColor);
    for (int i = 0; i < tabCount - 1; i++) {
        View tab = tabsContainer.getChildAt(i);
        canvas.drawLine(tab.getRight(), dividerPadding, tab.getRight(), 
 height - dividerPadding, dividerPaint);
    }
}

private class PageListener implements OnPageChangeListener {

    @Override
    public void onPageScrolled(int position, float positionOffset, int 
  positionOffsetPixels) {

        currentPosition = position;
        currentPositionOffset = positionOffset;


        System.out.println(position);
        System.out.println(positionOffset);
        System.out.println(positionOffset * 
 tabsContainer.getChildAt(position).getWidth());



        scrollToChild(position, (int) (positionOffset * 
 tabsContainer.getChildAt(position).getWidth()));

        invalidate();

        if (delegatePageListener != null) {
            delegatePageListener.onPageScrolled(position, 
positionOffset, positionOffsetPixels);
        }
    }

    @Override
    public void onPageScrollStateChanged(int state) {
        if (state == ViewPager.SCROLL_STATE_IDLE) {
            scrollToChild(pager.getCurrentItem(), 0);
        }

        if (delegatePageListener != null) {
            delegatePageListener.onPageScrollStateChanged(state);
        }
    }

    @Override
    public void onPageSelected(int position) {
        if (delegatePageListener != null) {
            delegatePageListener.onPageSelected(position);
        }
    }

}

public void setIndicatorColor(int indicatorColor) {
    this.indicatorColor = indicatorColor;
    invalidate();
}

public void setIndicatorColorResource(int resId) {
    this.indicatorColor = getResources().getColor(resId);
    invalidate();
}

public int getIndicatorColor() {
    return this.indicatorColor;
}

public void setIndicatorHeight(int indicatorLineHeightPx) {
    this.indicatorHeight = indicatorLineHeightPx;
    invalidate();
}

public int getIndicatorHeight() {
    return indicatorHeight;
}

public void setUnderlineColor(int underlineColor) {
    this.underlineColor = underlineColor;
    invalidate();
}

public void setUnderlineColorResource(int resId) {
    this.underlineColor = getResources().getColor(resId);
    invalidate();
}

public int getUnderlineColor() {
    return underlineColor;
}

public void setDividerColor(int dividerColor) {
    this.dividerColor = dividerColor;
    invalidate();
}

public void setDividerColorResource(int resId) {
    this.dividerColor = getResources().getColor(resId);
    invalidate();
}

public int getDividerColor() {
    return dividerColor;
}

public void setUnderlineHeight(int underlineHeightPx) {
    this.underlineHeight = underlineHeightPx;
    invalidate();
}

public int getUnderlineHeight() {
    return underlineHeight;
}

public void setDividerPadding(int dividerPaddingPx) {
    this.dividerPadding = dividerPaddingPx;
    invalidate();
}

public int getDividerPadding() {
    return dividerPadding;
}

public void setScrollOffset(int scrollOffsetPx) {
    this.scrollOffset = scrollOffsetPx;
    invalidate();
}

public int getScrollOffset() {
    return scrollOffset;
}

public void setShouldExpand(boolean shouldExpand) {
    this.shouldExpand = shouldExpand;
    requestLayout();
}

public boolean getShouldExpand() {
    return shouldExpand;
}

public boolean isTextAllCaps() {
    return textAllCaps;
}

public void setAllCaps(boolean textAllCaps) {
    this.textAllCaps = textAllCaps;
}

public void setTextSize(int textSizePx) {
    this.tabTextSize = textSizePx;
    updateTabStyles();
}

public int getTextSize() {
    return tabTextSize;
}

public void setTextColor(int textColor) {
    this.tabTextColor = textColor;
    updateTabStyles();
}

public void setTextColorResource(int resId) {
    this.tabTextColor = getResources().getColor(resId);
    updateTabStyles();
}

public int getTextColor() {
    return tabTextColor;
}

public void setTypeface(Typeface typeface, int style) {
    this.tabTypeface = typeface;
    this.tabTypefaceStyle = style;
    updateTabStyles();
}

public void setTabBackground(int resId) {
    this.tabBackgroundResId = resId;
}

public int getTabBackground() {
    return tabBackgroundResId;
}

public void setTabPaddingLeftRight(int paddingPx) {
    this.tabPadding = paddingPx;
    updateTabStyles();
}

public int getTabPaddingLeftRight() {
    return tabPadding;
}

@Override
public void onRestoreInstanceState(Parcelable state) {
    SavedState savedState = (SavedState) state;
    super.onRestoreInstanceState(savedState.getSuperState());
    currentPosition = savedState.currentPosition;
    requestLayout();
}

@Override
public Parcelable onSaveInstanceState() {
    Parcelable superState = super.onSaveInstanceState();
    SavedState savedState = new SavedState(superState);
    savedState.currentPosition = currentPosition;
    return savedState;
}

static class SavedState extends BaseSavedState {
    int currentPosition;

    public SavedState(Parcelable superState) {
        super(superState);
    }

    private SavedState(Parcel in) {
        super(in);
        currentPosition = in.readInt();
    }

    @Override
    public void writeToParcel(Parcel dest, int flags) {
        super.writeToParcel(dest, flags);
        dest.writeInt(currentPosition);
    }

    public static final Parcelable.Creator<SavedState> CREATOR = new  
 Parcelable.Creator<SavedState>() {
        @Override
        public SavedState createFromParcel(Parcel in) {
            return new SavedState(in);
        }

        @Override
        public SavedState[] newArray(int size) {
            return new SavedState[size];
        }
    };
}

---

我用过这个条件，现在可以了：

if(position!=0 && positionOffset!=0.0){
    scrollToChild(position, (int) (positionOffset *  
    tabsContainer.getChildAt(position).getWidth()));
}       

---

在屏幕中放置新文件后，需要执行getWidth（）等方法。要知道视图放置何时完成，请使用viewtreeobserver并获取该位置的宽度有趣的是，我不知道这一点，我将发布完整的代码，因此如果您能帮助我如何实现这一点，请。对此不确定，但我看到您使用的是canvas和onDraw方法，因此必须有一个名为onmeasure的方法尝试在该方法中获取宽度。vto在这里是不必要的，我想是的，但它太长了，好吧，我会发布，但我真的不希望有人阅读和帮助我：）我问…为什么你的代码中有空括号？你为什么需要空的街区？反转你的if条件！因为，我的应用程序正在创建与其源大小相等的选项卡，所以如果我的源为空，它不会创建任何选项卡：）这很好，但if是错误的。你不应该这样做：

if（xxx）{}else{//do}

。改为：

如果（！xxx）{//do}

这不适用于int，int不能为null如果你的意思是我做了一些类似if（i>0&&b>0）{xxx}的事情，那么仍然是不可能的，因为我的i可能是0，而我的b可能不是，条件仍然返回false

if(position!=0 && positionOffset!=0.0){
    scrollToChild(position, (int) (positionOffset *  
    tabsContainer.getChildAt(position).getWidth()));
}