获取Android控件的宽和高

Android初级教程_获取Android控件的宽和高

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:

[java] view
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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:

[java] view
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<com.test.MyImageView

android:id="@+id/imageview"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:src="@drawable/test" />

测试的Activity的onCreate():

[java] view
plaincopy

@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:

[java] view
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//------------------------------------------------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:

[java] view
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@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:

[java] view
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@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.

[java] view
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<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>

先来测试方法而:

[java] view
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@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

[java] view
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@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:



我想这方法二和方法三之间的区别就不用说了吧.

总结:那么需要获取控件的宽高该用那个方法呢?

方法一: 比其他的两个方法多了一次计算,也就是多调用了一次onMeasure()方法,该方法虽然看上去简单,但是如果要目标控件计算耗时比较大的话(如listView等),不建议使用.

方法二,它的回调方法会调用很多次,并且滑动TextView的时候任然会调用,所以不建议使用.

方法三,比较合适.

当然,实际应用的时候需要根据实际情况而定.