使用 getViewTreeObserver() 时 View.getHeight() 返回 0

Question

我试图在绘制之前获取 textView 高度，所以我使用其他问题中的 getViewTreeObserver 代码：

private TextView mTextView;
private int mTextViewHeight = 0;

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) { 
mRootView = inflater.inflate(R.layout.fragment, container, false);

mTextView = (TextView) mRootView.findViewById(R.id.text);

mTextView.getViewTreeObserver().addOnGlobalLayoutListener(
                new ViewTreeObserver.OnGlobalLayoutListener() {
                    @TargetApi(Build.VERSION_CODES.JELLY_BEAN)
                    @Override
                    public void onGlobalLayout() {
                        mTextViewHeight = mTextView.getHeight(); // Tried with getMeasured() too

                        if (Utils.hasJellyBean()) {
                            mTextView.getViewTreeObserver()
                                    .removeOnGlobalLayoutListener(this);
                        } else {
                            mTextView.getViewTreeObserver()
                                    .removeGlobalOnLayoutListener(this);
                        }
                    }
                });

使用此代码，我总是得到 mTextViewHeight = 0。我尝试过调试，并查看 OnGlobalLayoutListener 的入口点，线程永远不会访问“mTextViewHeight = mTextView.getHeight();”行。

谢谢！

编辑

答案很好，但我的错误是当我想在代码中使用 mTextViewHeight 时，这段代码是在进入监听器之前执行的，所以我得到的值是初始值。为了解决这个问题，我必须在侦听器中放入我想与 textView 高度一起使用的代码。

修复前：

private TextView mTextView;
    private int mTextViewHeight = 0;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                                 Bundle savedInstanceState) { 
    mRootView = inflater.inflate(R.layout.fragment, container, false);

    mTextView = (TextView) mRootView.findViewById(R.id.text);

    mTextView.getViewTreeObserver().addOnGlobalLayoutListener(
                    new ViewTreeObserver.OnGlobalLayoutListener() {
                        @TargetApi(Build.VERSION_CODES.JELLY_BEAN)
                        @Override
                        public void onGlobalLayout() {
                            mTextViewHeight = mTextView.getHeight(); // Tried with getMeasured() too

                            if (Utils.hasJellyBean()) {
                                mTextView.getViewTreeObserver()
                                        .removeOnGlobalLayoutListener(this);
                            } else {
                                mTextView.getViewTreeObserver()
                                        .removeGlobalOnLayoutListener(this);
                            }
                        }
                    });

    if(mTextViewHeight > maxHeightAllowed) {
        mTextViewHeight /= 2;
    } else {
        String text = new String("");
        for(int i = 0; i < mTextViewHeight.lenght(); i++)
        text = text + getNextWord[i];
    }
}

修复后

private TextView mTextView;
private int mTextViewHeight = 0;

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) { 
mRootView = inflater.inflate(R.layout.fragment, container, false);

mTextView = (TextView) mRootView.findViewById(R.id.text);

mTextView.getViewTreeObserver().addOnGlobalLayoutListener(
                new ViewTreeObserver.OnGlobalLayoutListener() {
                    @TargetApi(Build.VERSION_CODES.JELLY_BEAN)
                    @Override
                    public void onGlobalLayout() {
                        mTextViewHeight = mTextView.getHeight(); // Tried with getMeasured() too
                        if(mTextViewHeight > maxHeightAllowed) {
                            mTextViewHeight /= 2;
                        } else {
                            String text = new String("");
                            for(int i = 0; i < mTextViewHeight.lenght(); i++)
                            text = text + getNextWord[i];
                        }

                        if (Utils.hasJellyBean()) {
                            mTextView.getViewTreeObserver()
                                    .removeOnGlobalLayoutListener(this);
                        } else {
                            mTextView.getViewTreeObserver()
                                    .removeGlobalOnLayoutListener(this);
                        }
                    }
                });

}

Answer 1

我认为你应该使用onPreDraw函数：

    ViewTreeObserver greenObserver = mTextViewHeight.getViewTreeObserver();
    greenObserver.addOnPreDrawListener(new OnPreDrawListener() {

        @Override
        public boolean onPreDraw() {
            mTextViewHeight.getViewTreeObserver().removeOnPreDrawListener(this);
            System.out.println("The height is " + mTextViewHeight.getHeight());
            return true;
        }
    });