我什么时候可以测量一个视图？ [英] When Can I First Measure a View?

问题描述

所以我有一个有点混乱，试图建立一个视图的背景绘制的，因为它是显示。在code依靠知道观的高度，所以我不能从的onCreate（）或 onResume（），因为的getHeight（）返回0 onResume（）似乎是最接近我能得到虽然。我应该在哪里把code如下面，这样在显示背景的变化给用户？

  TextView的电视=（TextView中）findViewById（R.id.image_test）;
    LayerDrawable LD =（LayerDrawable）tv.getBackground（）;
    INT高= tv.getHeight（）; //当调用此以免得到0？
    INT topInset =身高/ 2;
    ld.setLayerInset（1，0，topInset，0，0）;
    tv.setBackgroundDrawable（LD）;
 

解决方案

我不知道 ViewTreeObserver.addOn preDrawListener（），我试了一下在一个测试项目。

使用您的code就应该是这样的：

 公共无效的onCreate（）{
的setContentView（R.layout.main）;

最后的TextView电视=（TextView中）findViewById（R.id.image_test）;
最后LayerDrawable LD =（LayerDrawable）tv.getBackground（）;
最终ViewTreeObserver观测值= mTv.getViewTreeObserver（）;
obs.addOn preDrawListener（新ViewTreeObserver.On preDrawListener（）{
    @覆盖
    在preDraw公共布尔（）{
        Log.d（TAG，在preDraw电视高度+ tv.getHeight（））; //不好的表现，除去生产
        INT高= tv.getHeight（）;
        INT topInset =身高/ 2;
        ld.setLayerInset（1，0，topInset，0，0）;
        tv.setBackgroundDrawable（LD）;

        返回true;
   }
}）;
}
 

在我的测试项目在preDraw（）已叫了两声，我认为你的情况可能会导致一个无限循环。

您可以尝试调用 setBackgroundDrawable（）只有当的的TextView 的高度变化：

 私人INT mLastTvHeight = 0;

公共无效的onCreate（）{
的setContentView（R.layout.main）;

最后的TextView电视=（TextView中）findViewById（R.id.image_test）;
最后LayerDrawable LD =（LayerDrawable）tv.getBackground（）;
最终ViewTreeObserver观测值= mTv.getViewTreeObserver（）;
obs.addOn preDrawListener（新ViewTreeObserver.On preDrawListener（）{
    @覆盖
    在preDraw公共布尔（）{
        Log.d（TAG，在preDraw电视高度+ tv.getHeight（））; //不好的表现，除去生产
        INT高= tv.getHeight（）;
        如果（高度！= mLastTvHeight）{
            mLastTvHeight =高度;
            INT topInset =身高/ 2;
            ld.setLayerInset（1，0，topInset，0，0）;
            tv.setBackgroundDrawable（LD）;
        }

        返回true;
   }
}）;
}
 

不过，这听起来有点复杂，你要实现的目标和业绩不是很好的东西。

修改通过kcoppock

下面是我最终从这个code做的事情。戈蒂埃的回答让我到这一点，所以我宁愿接受这个答案与修改回答比我自己​​。最后我用了ViewTreeObserver的addOnGlobalLayoutListener（）方法来代替，像这样（这是的onCreate（））：

 最后的TextView电视=（TextView中）findViewById（R.id.image_test）;
ViewTreeObserver VTO = tv.getViewTreeObserver（）;
vto.addOnGlobalLayoutListener（新OnGlobalLayoutListener（）{
    @覆盖
    公共无效onGlobalLayout（）{
        LayerDrawable LD =（LayerDrawable）tv.getBackground（）;
        ld.setLayerInset（1，0，tv.getHeight（）/ 2，0，0）;
    }
}）;
 

似乎很好地工作;我检查LogCat中，并没有看到任何异常活动。但愿这是它！谢谢！

So I have a bit of confusion with trying to set the background drawable of a view as it is displayed. The code relies upon knowing the height of the view, so I can't call it from onCreate() or onResume(), because getHeight() returns 0. onResume() seems to be the closest I can get though. Where should I put code such as the below so that the background changes upon display to the user?

    TextView tv = (TextView)findViewById(R.id.image_test);
    LayerDrawable ld = (LayerDrawable)tv.getBackground();
    int height = tv.getHeight(); //when to call this so as not to get 0?
    int topInset = height / 2;
    ld.setLayerInset(1, 0, topInset, 0, 0);
    tv.setBackgroundDrawable(ld);

解决方案

I didn't know about ViewTreeObserver.addOnPreDrawListener(), and I tried it in a test project.

With your code it would look like this:

public void onCreate() {
setContentView(R.layout.main);

final TextView tv = (TextView)findViewById(R.id.image_test);
final LayerDrawable ld = (LayerDrawable)tv.getBackground();
final ViewTreeObserver obs = mTv.getViewTreeObserver();
obs.addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
    @Override
    public boolean onPreDraw () {
        Log.d(TAG, "onPreDraw tv height is " + tv.getHeight()); // bad for performance, remove on production
        int height = tv.getHeight();
        int topInset = height / 2;
        ld.setLayerInset(1, 0, topInset, 0, 0);
        tv.setBackgroundDrawable(ld);

        return true;
   }
});
}

In my test project onPreDraw() has been called twice, and I think in your case it may cause an infinite loop.

You could try to call the setBackgroundDrawable() only when the height of the TextView changes :

private int mLastTvHeight = 0;

public void onCreate() {
setContentView(R.layout.main);

final TextView tv = (TextView)findViewById(R.id.image_test);
final LayerDrawable ld = (LayerDrawable)tv.getBackground();
final ViewTreeObserver obs = mTv.getViewTreeObserver();
obs.addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
    @Override
    public boolean onPreDraw () {
        Log.d(TAG, "onPreDraw tv height is " + tv.getHeight()); // bad for performance, remove on production
        int height = tv.getHeight();
        if (height != mLastTvHeight) {
            mLastTvHeight = height;
            int topInset = height / 2;
            ld.setLayerInset(1, 0, topInset, 0, 0);
            tv.setBackgroundDrawable(ld);
        }

        return true;
   }
});
}

But that sounds a bit complicated for what you are trying to achieve and not really good for performance.

EDIT by kcoppock

Here's what I ended up doing from this code. Gautier's answer got me to this point, so I'd rather accept this answer with modification than answer it myself. I ended up using the ViewTreeObserver's addOnGlobalLayoutListener() method instead, like so (this is in onCreate()):

final TextView tv = (TextView)findViewById(R.id.image_test);
ViewTreeObserver vto = tv.getViewTreeObserver();
vto.addOnGlobalLayoutListener(new OnGlobalLayoutListener() {
    @Override
    public void onGlobalLayout() {
        LayerDrawable ld = (LayerDrawable)tv.getBackground();
        ld.setLayerInset(1, 0, tv.getHeight() / 2, 0, 0);
    }
});

Seems to work perfectly; I checked LogCat and didn't see any unusual activity. Hopefully this is it! Thanks!

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