Android 获取控件高度宽度三种方法,防止0的出现

来源：互联网发布：淘宝魔盒有什么用编辑：程序博客网时间：2024/06/08 00:32

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:

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publicclass MyImageView extendsImageView { 
 
publicMyImageView(Context context, AttributeSet attrs) { 
super(context, attrs); 
}
publicMyImageView(Context context) { 
super(context);
}
 
@Override
protectedvoid onMeasure(intwidthMeasureSpec, intheightMeasureSpec) { 
super.onMeasure(widthMeasureSpec, heightMeasureSpec); 
System.out.println("onMeasure 我被调用了"+System.currentTimeMillis());
}
 
@Override
protectedvoid onDraw(Canvas canvas) { 
super.onDraw(canvas);
System.out.println("onDraw 我被调用了"+System.currentTimeMillis());
}
}

布局

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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"/>

oncreate：

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

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:

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//------------------------------------------------方法一
intw = View.MeasureSpec.makeMeasureSpec(0,View.MeasureSpec.UNSPECIFIED);
inth = View.MeasureSpec.makeMeasureSpec(0,View.MeasureSpec.UNSPECIFIED);
imageView.measure(w, h); 
intheight =imageView.getMeasuredHeight(); 
intwidth =imageView.getMeasuredWidth(); 
textView.append("\n"+height+","+width);
 
 
 
 
//-----------------------------------------------方法二
ViewTreeObserver vto = imageView.getViewTreeObserver(); 
vto.addOnPreDrawListener(newViewTreeObserver.OnPreDrawListener() { 
publicboolean onPreDraw() { 
intheight = imageView.getMeasuredHeight(); 
intwidth = imageView.getMeasuredWidth(); 
textView.append("\n"+height+","+width);
returntrue;
}
});
//-----------------------------------------------方法三
ViewTreeObserver vto2 = imageView.getViewTreeObserver(); 
vto2.addOnGlobalLayoutListener(newOnGlobalLayoutListener() { 
@Override
publicvoid onGlobalLayout() { 
imageView.getViewTreeObserver().removeGlobalOnLayoutListener(this);
textView.append("\n\n"+imageView.getHeight()+","+imageView.getWidth());
}
});

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:

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publicvoid onCreate(Bundle savedInstanceState) { 
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
finalImageView imageView = (ImageView) findViewById(R.id.imageview); 
 
//------------------------------------------------方法一
intw = View.MeasureSpec.makeMeasureSpec(0,View.MeasureSpec.UNSPECIFIED);
inth = View.MeasureSpec.makeMeasureSpec(0,View.MeasureSpec.UNSPECIFIED);
imageView.measure(w, h); 
intheight =imageView.getMeasuredHeight(); 
intwidth =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:

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publicvoid onCreate(Bundle savedInstanceState) { 
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
finalImageView imageView = (ImageView) findViewById(R.id.imageview); 
-----------------------------------------------方法二
ViewTreeObserver vto = imageView.getViewTreeObserver(); 
vto.addOnPreDrawListener(newViewTreeObserver.OnPreDrawListener() { 
publicboolean onPreDraw() { 
intheight = imageView.getMeasuredHeight(); 
intwidth = imageView.getMeasuredWidth(); 
textView.append("\n"+height+","+width);
returntrue;
}
});
}

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.

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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>

先来测试方法二:

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publicvoid onCreate(Bundle savedInstanceState) { 
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
finalImageView imageView = (ImageView) findViewById(R.id.imageview); 
-----------------------------------------------方法二
ViewTreeObserver vto = imageView.getViewTreeObserver(); 
vto.addOnPreDrawListener(newViewTreeObserver.OnPreDrawListener() { 
publicboolean onPreDraw() { 
intheight = imageView.getMeasuredHeight(); 
intwidth = imageView.getMeasuredWidth(); 
textView.append("\n"+height+","+width);
returntrue;
}
});
}

再来测试方法三

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

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,不见时使用,如listView等.
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.

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