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Android 获取控件高度宽度三种方法,防止0的出现

2014-04-11 16:40 417 查看
转自：http://my.oschina.net/xiahuawuyu/blog/167949

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:

01
public
class
MyImageView
extends
ImageView
{
02
03
public
MyImageView(Context
context, AttributeSet attrs) {
04
super
(context,
attrs);
05
}
06
public
MyImageView(Context
context) {
07
super
(context);
08
}
09
10
@Override
11
protected
void
onMeasure(
int
widthMeasureSpec,
int
heightMeasureSpec)
{
12
super
.onMeasure(widthMeasureSpec,
heightMeasureSpec);
13
System.out.println(
"onMeasure
我被调用了"
+System.currentTimeMillis());
14
}
15
16
@Override
17
protected
void
onDraw(Canvas
canvas) {
18
super
.onDraw(canvas);
19
System.out.println(
"onDraw
我被调用了"
+System.currentTimeMillis());
20
}
21
}
布局

1
<
com.test.MyImageView
2
android:id
=
"@+id/imageview"
3
android:layout_width
=
"wrap_content"
4
android:layout_height
=
"wrap_content"
5
android:src
=
"@drawable/test"
/>
oncreate：

1
@Override
2
public
void
onCreate(Bundle
savedInstanceState) {
3
super
.onCreate(savedInstanceState);
4
setContentView(R.layout.main);
5
System.out.println(
"执行完毕.."
+System.currentTimeMillis());
6
}
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:

01
//------------------------------------------------方法一
02
int
w
= View.MeasureSpec.makeMeasureSpec(
0
,View.MeasureSpec.UNSPECIFIED);
03
int
h
= View.MeasureSpec.makeMeasureSpec(
0
,View.MeasureSpec.UNSPECIFIED);
04
imageView.measure(w,
h);
05
int
height
=imageView.getMeasuredHeight();
06
int
width
=imageView.getMeasuredWidth();
07
textView.append(
"\n"
+height+
","
+width);
08
09
10
11
12
//-----------------------------------------------方法二
13
ViewTreeObserver
vto = imageView.getViewTreeObserver();
14
vto.addOnPreDrawListener(
new
ViewTreeObserver.OnPreDrawListener()
{
15
public
boolean
onPreDraw()
{
16
int
height
= imageView.getMeasuredHeight();
17
int
width
= imageView.getMeasuredWidth();
18
textView.append(
"\n"
+height+
","
+width);
19
return
true
;
20
}
21
});
22
//-----------------------------------------------方法三
23
ViewTreeObserver
vto2 = imageView.getViewTreeObserver();
24
vto2.addOnGlobalLayoutListener(
new
OnGlobalLayoutListener()
{
25
@Override
26
public
void
onGlobalLayout()
{
27
imageView.getViewTreeObserver().removeGlobalOnLayoutListener(
this
);
28
textView.append(
"\n\n"
+imageView.getHeight()+
","
+imageView.getWidth());
29
}
30
});
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:

01
public
void
onCreate(Bundle
savedInstanceState) {
02
super
.onCreate(savedInstanceState);
03
setContentView(R.layout.main);
04
final
ImageView
imageView = (ImageView) findViewById(R.id.imageview);
05
06
//------------------------------------------------方法一
07
int
w
= View.MeasureSpec.makeMeasureSpec(
0
,View.MeasureSpec.UNSPECIFIED);
08
int
h
= View.MeasureSpec.makeMeasureSpec(
0
,View.MeasureSpec.UNSPECIFIED);
09
imageView.measure(w,
h);
10
int
height
=imageView.getMeasuredHeight();
11
int
width
=imageView.getMeasuredWidth();
12
textView.append(
"\n"
+height+
","
+width);
13
14
System.out.println(
"执行完毕.."
+System.currentTimeMillis());
15
}
接着来看下面几种方式输出结果:

把测试Activity改成如下:

01
public
void
onCreate(Bundle
savedInstanceState) {
02
super
.onCreate(savedInstanceState);
03
setContentView(R.layout.main);
04
final
ImageView
imageView = (ImageView) findViewById(R.id.imageview);
05
-----------------------------------------------方法二
06
ViewTreeObserver
vto = imageView.getViewTreeObserver();
07
vto.addOnPreDrawListener(
new
ViewTreeObserver.OnPreDrawListener()
{
08
public
boolean
onPreDraw()
{
09
int
height
= imageView.getMeasuredHeight();
10
int
width
= imageView.getMeasuredWidth();
11
textView.append(
"\n"
+height+
","
+width);
12
return
true
;
13
}
14
});
15
}
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.

1
<
ScrollView
2
android:layout_width
=
"wrap_content"
3
android:layout_height
=
"wrap_content"
>
4
5
<
TextView
6
android:id
=
"@+id/text"
7
android:layout_width
=
"wrap_content"
8
android:layout_height
=
"wrap_content"
/>
9
</
ScrollView
>
先来测试方法二:

01
public
void
onCreate(Bundle
savedInstanceState) {
02
super
.onCreate(savedInstanceState);
03
setContentView(R.layout.main);
04
final
ImageView
imageView = (ImageView) findViewById(R.id.imageview);
05
-----------------------------------------------方法二
06
ViewTreeObserver
vto = imageView.getViewTreeObserver();
07
vto.addOnPreDrawListener(
new
ViewTreeObserver.OnPreDrawListener()
{
08
public
boolean
onPreDraw()
{
09
int
height
= imageView.getMeasuredHeight();
10
int
width
= imageView.getMeasuredWidth();
11
textView.append(
"\n"
+height+
","
+width);
12
return
true
;
13
}
14
});
15
}




再来测试方法三

01
public
void
onCreate(Bundle
savedInstanceState) {
02
super
.onCreate(savedInstanceState);
03
setContentView(R.layout.main);
04
final
ImageView
imageView = (ImageView) findViewById(R.id.imageview);
05
//-----------------------------------------------方法三
06
ViewTreeObserver
vto2 = imageView.getViewTreeObserver();
07
vto2.addOnGlobalLayoutListener(
new
OnGlobalLayoutListener()
{
08
@Override
09
public
void
onGlobalLayout()
{
10
imageView.getViewTreeObserver().removeGlobalOnLayoutListener(
this
);
11
textView.append(
"\n\n"
+imageView.getHeight()+
","
+imageView.getWidth());
12
}
13
});
14
}




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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标签：  控件 布局
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