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 plain copy 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 plain copy <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 plain copy @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 plain copy //------------------------------------------------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 plain copy @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 plain copy @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 plain copy <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 plain copy @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 plain copy @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.
谢谢!! 欢迎转载:http://blog.csdn.net/johnny901114/article/details/7839512
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 plain copy 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 plain copy <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 plain copy @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 plain copy //------------------------------------------------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 plain copy @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 plain copy @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 plain copy <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 plain copy @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 plain copy @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.
谢谢!! 欢迎转载:http://blog.csdn.net/johnny901114/article/details/7839512
