我正在动态地创建我的android项目中的所有元素。我试图获得一个按钮的宽度和高度,以便我可以旋转该按钮。我只是想学习如何使用android语言。但是,它返回0。
我做了一些研究,我看到它需要在其他地方而不是在onCreate()方法中完成。如果有人能给我一个如何做这件事的例子,那就太好了。
这是我当前的代码:
package com.animation;
import android.app.Activity;
import android.os.Bundle;
import android.view.animation.Animation;
import android.view.animation.LinearInterpolator;
import android.view.animation.RotateAnimation;
import android.widget.Button;
import android.widget.LinearLayout;
public class AnimateScreen extends Activity {
//Called when the activity is first created.
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
LinearLayout ll = new LinearLayout(this);
LinearLayout.LayoutParams layoutParams = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.WRAP_CONTENT, LinearLayout.LayoutParams.WRAP_CONTENT);
layoutParams.setMargins(30, 20, 30, 0);
Button bt = new Button(this);
bt.setText(String.valueOf(bt.getWidth()));
RotateAnimation ra = new RotateAnimation(0,360,bt.getWidth() / 2,bt.getHeight() / 2);
ra.setDuration(3000L);
ra.setRepeatMode(Animation.RESTART);
ra.setRepeatCount(Animation.INFINITE);
ra.setInterpolator(new LinearInterpolator());
bt.startAnimation(ra);
ll.addView(bt,layoutParams);
setContentView(ll);
}
任何帮助都是感激的。
正如Ian在这篇Android开发者文章中所述:
Anyhow, the deal is that layout of the
contents of a window happens
after all the elements are constructed and added to their parent
views. It has to be this way, because
until you know what components a View
contains, and what they contain, and
so on, there's no sensible way you can
lay it out.
Bottom line, if you call getWidth()
etc. in a constructor, it will return
zero. The procedure is to create all
your view elements in the constructor,
then wait for your View's
onSizeChanged() method to be called --
that's when you first find out your
real size, so that's when you set up
the sizes of your GUI elements.
Be aware too that onSizeChanged() is
sometimes called with parameters of
zero -- check for this case, and
return immediately (so you don't get a
divide by zero when calculating your
layout, etc.). Some time later it
will be called with the real values.
带post的答案是不正确的,因为大小可能无法重新计算。
另一个重要的事情是视图和所有它的祖先必须是可见的。为此,我使用属性view . isshows。
下面是我的kotlin函数,它可以放在utils中的某个地方:
fun View.onInitialized(onInit: () -> Unit) {
viewTreeObserver.addOnGlobalLayoutListener(object : OnGlobalLayoutListener {
override fun onGlobalLayout() {
if (isShown) {
viewTreeObserver.removeOnGlobalLayoutListener(this)
onInit()
}
}
})
}
用法是:
myView.onInitialized {
Log.d(TAG, "width is: " + myView.width)
}
你可以使用addOnLayoutChangeListener
你可以在onCreate活动或onCreateView片段中使用它
@Edit
不要忘记删除它,因为在某些情况下它会触发无限循环
myView.addOnLayoutChangeListener(object : View.OnLayoutChangeListener{
override fun onLayoutChange(
v: View?, left: Int, top: Int, right: Int, bottom: Int, oldLeft: Int, oldTop: Int, oldRight: Int, oldBottom: Int
) {
if (v?.width > 0 && v?.height > 0){
// do something
Log.i(TAG, "view : ${view.width}")
// remove after finish
v?.removeOnLayoutChangeListener(this)
}
}
})