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。


当前回答

AndroidX在AndroidX .core.view中有多个扩展函数可以帮助你完成这类工作

为此,您需要使用Kotlin。

最适合这里的是doOnLayout:

在布局此视图时执行给定的操作。如果视图已经布局并且它没有请求布局,操作将立即执行,否则,操作将在视图下一次布局后执行。 该操作只会在下一个布局中被调用一次,然后被删除。

在你的例子中:

bt.doOnLayout {
    val ra = RotateAnimation(0,360,it.width / 2,it.height / 2)
    // more code
}

依赖:androidx.core: core-ktx: 1.0.0

其他回答

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)
}

我们可以用

@Override
 public void onWindowFocusChanged(boolean hasFocus) {
  super.onWindowFocusChanged(hasFocus);
  //Here you can get the size!
 }

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.

一个Kotlin扩展来观察全局布局,并在高度动态就绪时执行给定的任务。

用法:

view.height { Log.i("Info", "Here is your height:" + it) }

实现:

fun <T : View> T.height(function: (Int) -> Unit) {
    if (height == 0)
        viewTreeObserver.addOnGlobalLayoutListener(object : ViewTreeObserver.OnGlobalLayoutListener {
            override fun onGlobalLayout() {
                viewTreeObserver.removeOnGlobalLayoutListener(this)
                function(height)
            }
        })
    else function(height)
}

这是一个有点旧,但我自己有麻烦(需要在一个片段中创建动画对象)。这个解决方案对我来说很有效,我相信这是不言自明的。

class YourFragment: Fragment() {
    var width = 0
    var height = 0


override fun onCreateView(
    inflater: LayoutInflater, container: ViewGroup?,
    savedInstanceState: Bundle?
): View? {
    // Inflate the layout for this fragment
    val root = inflater.inflate(R.layout.fragment_winner_splash, container, false)
    container?.width.let {
        if (it != null) {
            width = it
        }
    }
    container?.height.let {
        if (it != null) {
            height = it
        }
    }
    
    return root
}