Android编程获取控件宽和高的方法总结分析

2022-06-06 09:14

短信预约 -IT技能 免费直播动态提醒

本文总结分析了Android编程获取控件宽和高的方法。分享给大家供大家参考，具体如下：

我们都知道在onCreate()里面获取控件的高度是0,这是为什么呢?我们来看一下示例:

首先我们自己写一个控件,这个控件非常简单:


public class MyImageView extends ImageView {
  public MyImageView(Context context, AttributeSet attrs) {
    super(context, attrs);
  }
  public MyImageView(Context context) {
    super(context);
  }
  @Override
  protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    System.out.println("onMeasure 我被调用了"+System.currentTimeMillis());
  }
  @Override
  protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    System.out.println("onDraw 我被调用了"+System.currentTimeMillis());
  }
}

布局文件:


<com.test.MyImageView
  android:id="@+id/imageview"
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:class="lazy" data-src="@drawable/test" />

测试的Activity的onCreate():


@Override
public void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.main);
  System.out.println("执行完毕.."+System.currentTimeMillis());
}

现在我们现在来看一下结果:

说明等onCreate方法执行完了,我们定义的控件才会被度量(measure),所以我们在onCreate方法里面通过view.getHeight()获取控件的高度或者宽度肯定是0,因为它自己还没有被度量,也就是说他自己都不知道自己有多高,而你这时候去获取它的尺寸,肯定是不行的.

现在碰到这个问题我们不能不解决,在网上找到了如下办法:


//------------------------------------------------方法一
int w = View.MeasureSpec.makeMeasureSpec(0,View.MeasureSpec.UNSPECIFIED);
int h = View.MeasureSpec.makeMeasureSpec(0,View.MeasureSpec.UNSPECIFIED);
imageView.measure(w, h);
int height =imageView.getMeasuredHeight();
int width =imageView.getMeasuredWidth();
textView.append("\n"+height+","+width);
//-----------------------------------------------方法二
ViewTreeObserver vto = imageView.getViewTreeObserver();
vto.addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
  public boolean onPreDraw() {
    int height = imageView.getMeasuredHeight();
    int width = imageView.getMeasuredWidth();
    textView.append("\n"+height+","+width);
    return true;
  }
});
//-----------------------------------------------方法三
ViewTreeObserver vto2 = imageView.getViewTreeObserver();
vto2.addOnGlobalLayoutListener(new OnGlobalLayoutListener() {
  @Override
  public void onGlobalLayout() {
    imageView.getViewTreeObserver().removeGlobalOnLayoutListener(this);
    textView.append("\n\n"+imageView.getHeight()+","+imageView.getWidth());
  }
});

这三个方法是哪里找到现在已经忘了.

现在要讨论的是当我们需要时候使用哪个方法呢?

现在把测试的Activity改成如下:


@Override
 public void onCreate(Bundle savedInstanceState) {
   super.onCreate(savedInstanceState);
   setContentView(R.layout.main);
   final ImageView imageView = (ImageView) findViewById(R.id.imageview);
   //------------------------------------------------方法一
   int w = View.MeasureSpec.makeMeasureSpec(0,View.MeasureSpec.UNSPECIFIED);
   int h = View.MeasureSpec.makeMeasureSpec(0,View.MeasureSpec.UNSPECIFIED);
   imageView.measure(w, h);
   int height =imageView.getMeasuredHeight();
   int width =imageView.getMeasuredWidth();
   textView.append("\n"+height+","+width);
   System.out.println("执行完毕.."+System.currentTimeMillis());
 }

接着来看下面几种方式输出结果:

把测试Activity改成如下:


@Override
public void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.main);
  final ImageView imageView = (ImageView) findViewById(R.id.imageview);
//-----------------------------------------------方法二
  ViewTreeObserver vto = imageView.getViewTreeObserver();
  vto.addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
    public boolean onPreDraw() {
      int height = imageView.getMeasuredHeight();
      int width = imageView.getMeasuredWidth();
      textView.append("\n"+height+","+width);
      return true;
    }
  });
}

结果如下:

方法三就不再测试了同方法二!!!

那么方法而和方法三在执行上有什么区别呢?

我们在布局文件中加入一个TextView来记录这个控件的宽高.


<ScrollView
  android:layout_width="wrap_content"
  android:layout_height="wrap_content" >
  <TextView
    android:id="@+id/text"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content" />
</ScrollView>

先来测试方法二:


@Override
public void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.main);
  final ImageView imageView = (ImageView) findViewById(R.id.imageview);
//-----------------------------------------------方法二
  ViewTreeObserver vto = imageView.getViewTreeObserver();
  vto.addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
    public boolean onPreDraw() {
      int height = imageView.getMeasuredHeight();
      int width = imageView.getMeasuredWidth();
      textView.append("\n"+height+","+width);
      return true;
    }
  });
}

结果如下:

我们再来测试方法三


@Override
public void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.main);
  final ImageView imageView = (ImageView) findViewById(R.id.imageview);
  //-----------------------------------------------方法三
  ViewTreeObserver vto2 = imageView.getViewTreeObserver();
  vto2.addOnGlobalLayoutListener(new OnGlobalLayoutListener() {
    @Override
    public void onGlobalLayout() {
      imageView.getViewTreeObserver().removeGlobalOnLayoutListener(this);
      textView.append("\n\n"+imageView.getHeight()+","+imageView.getWidth());
    }
  });
}

输出结果如下: