我试图用这个code从活动采取截图，但我在与code线得到一个显示java.lang.NullPointerException：

 位图B = Bitmap.createBitmap（view.getDrawingCache（），0，statusBarHeight，宽度，高度 -  statusBarHeight） 

，当我试图调试我发现，所有的变量都无法解决;即，statusBarHeight，宽度，高度。请帮我解决这个。

 活动AV;查看视图。@覆盖公共无效的onCreate（捆绑savedInstanceState）{    super.onCreate（savedInstanceState）;    的setContentView（R.layout.main）;    鉴于=（查看）findViewById（R.id.screen）;    AV = HelloAndroidActivity.this;    尝试{    takeScreenShot（AV）;    }    赶上（例外五）    {}}公共无效takeScreenShot（活动AV）抛出异常{    查看= this.getWindow（）getDecorView（）;    //要么    //视图= av.getWindow（）getDecorView（）。    view.setDrawingCacheEnabled（真）;    view.buildDrawingCache（真）;    位图B1 = view.getDrawingCache（）;    矩形框=新的矩形（）;    。this.getWindow（）getDecorView（）getWindowVisibleDisplayFrame（帧）。    INT statusBarHeight = frame.top;    INT宽度= this.getWindowManager（）getDefaultDisplay（）的getWidth（）。    INT高度= this.getWindowManager（）getDefaultDisplay（）的getHeight（）。    位图B = Bitmap.createBitmap（view.getDrawingCache（），0，statusBarHeight，宽度，高度 -  statusBarHeight）;    view.destroyDrawingCache（）;    FOS的FileOutputStream = NULL;    尝试    {        //文件sddir =新的文件（路径名）;        文件根= Environment.getExternalStorageDirectory（）;        // S = sddir.toString（）;        Toast.makeText（这一点，路径+根，Toast.LENGTH_LONG）.show（）;        如果（！root.exists（））        {            root.mkdirs（）;        }        FOS =新的FileOutputStream（根+/图片+_+4+.JPEG）;        如果（FOS！= NULL）        {            b.com preSS（Bitmap.Com pressFormat.JPEG，90，FOS）;            fos.flush（）;            fos.close（）;        }    }    赶上（例外五）    {        Toast.makeText（这一点，异常+ E，Toast.LENGTH_LONG）.show（）;        Log.e（，而动态图像时出现异常：e.toString（））;        e.printStackTrace（）;    }} 

解决方案

使用以下code避免的无效的位图：

 公共类AndroidWebImage延伸活动{ImageView的bmImage;观的LinearLayout;  / **当第一次创建活动调用。 * /  @覆盖  公共无效的onCreate（捆绑savedInstanceState）{      super.onCreate（savedInstanceState）;      的setContentView（R.layout.main）;      鉴于=（的LinearLayout）findViewById（R.id.screen）;      bmImage =（ImageView的）findViewById（R.id.image）;      view.setDrawingCacheEnabled（真）;      //这是最重要的code :)      //没有它的视图将具有0,0维和位图将为空      view.measure（MeasureSpec.makeMeasureSpec（0，MeasureSpec.UNSPECIFIED），            MeasureSpec.makeMeasureSpec（0，MeasureSpec.UNSPECIFIED））;      view.layout（0，0，view.getMeasuredWidth（），view.getMeasuredHeight（））;      view.buildDrawingCache（真）;      位图B = Bitmap.createBitmap（view.getDrawingCache（））;      view.setDrawingCacheEnabled（假）; //明确绘图缓存      bmImage.setImageBitmap（二）;};} 

好好看看，你必须使用：

  view.measure（MeasureSpec.makeMeasureSpec（0，MeasureSpec.UNSPECIFIED）                MeasureSpec.makeMeasureSpec（0，MeasureSpec.UNSPECIFIED））; view.layout（0，0，view.getMeasuredWidth（），view.getMeasuredHeight（））; 

我用下面的 main.xml中

 ＆LT;？XML版本=1.0编码=UTF-8＆GT？;＆LT; LinearLayout中的xmlns：机器人=htt​​p://schemas.android.com/apk/res/android  机器人：方向=垂直   机器人：ID =@ + ID /屏幕  机器人：layout_width =FILL_PARENT  机器人：layout_height =FILL_PARENT  ＆GT;＆LT;的TextView  机器人：layout_width =FILL_PARENT  机器人：layout_height =WRAP_CONTENT  机器人：文字=@字符串/你好  /＆GT;＆LT; ImageView的  机器人：ID =@ + ID /图像  机器人：layout_width =FILL_PARENT  机器人：layout_height =FILL_PARENT/＆GT;＆LT; / LinearLayout中＆GT; 

的结果是：

Reference

I am trying to use this code to take a screenshot from the activity but I am getting a java.lang.nullpointerexception at a line with the code:

Bitmap b = Bitmap.createBitmap(view.getDrawingCache(), 0, statusBarHeight, width, height - statusBarHeight)

and when I tried to debug I found that all the variables are not able to resolve; i.e., statusBarHeight, width, height. Please help me in resolving this.

Activity av; 
View view;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    view = (View)findViewById(R.id.screen);
    av= HelloAndroidActivity.this;

    try {   
    takeScreenShot(av);
    }
    catch (Exception e) 
    { }
}  

public void takeScreenShot(Activity av) throws Exception 
{ 
    view =this.getWindow().getDecorView();
    //or
    //view =av.getWindow().getDecorView();

    view.setDrawingCacheEnabled(true); 
    view.buildDrawingCache(true);           

    Bitmap b1 = view.getDrawingCache();
    Rect frame = new Rect();
    this.getWindow().getDecorView().getWindowVisibleDisplayFrame(frame);
    int statusBarHeight = frame.top;
    int width = this.getWindowManager().getDefaultDisplay().getWidth();
    int height = this.getWindowManager().getDefaultDisplay().getHeight();

    Bitmap b = Bitmap.createBitmap(view.getDrawingCache(), 0, statusBarHeight, width, height - statusBarHeight);
    view.destroyDrawingCache();

    FileOutputStream fos = null; 

    try 
    { 
        //File sddir = new File(path, name);
        File root = Environment.getExternalStorageDirectory();

        //s= sddir.toString();
        Toast.makeText(this, "path " + root, Toast.LENGTH_LONG).show();

        if (!root.exists()) 
        { 
            root.mkdirs(); 
        }               

        fos = new FileOutputStream(root+ "/Image" + "_" + "4" + ".jpeg");              

        if (fos != null) 
        { 
            b.compress(Bitmap.CompressFormat.JPEG, 90, fos); 
            fos.flush();
            fos.close();                  
        } 
    } 
    catch (Exception e) 
    { 
        Toast.makeText(this, "Exception " + e, Toast.LENGTH_LONG).show();
        Log.e("Exception occurred while moving image: ",  e.toString());
        e.printStackTrace();
    } 
} 

Use the following code to avoid a null bitmap:

public class AndroidWebImage extends Activity {

ImageView bmImage; 
LinearLayout view;
  /** Called when the activity is first created. */
  @Override
  public void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.main);

      view = (LinearLayout)findViewById(R.id.screen);
      bmImage = (ImageView)findViewById(R.id.image);

      view.setDrawingCacheEnabled(true);
      // this is the important code :)  
      // Without it the view will have a dimension of 0,0 and the bitmap will be null          

      view.measure(MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED), 
            MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED));

      view.layout(0, 0, view.getMeasuredWidth(), view.getMeasuredHeight()); 

      view.buildDrawingCache(true);
      Bitmap b = Bitmap.createBitmap(view.getDrawingCache());
      view.setDrawingCacheEnabled(false); // clear drawing cache

      bmImage.setImageBitmap(b);   

};


}

Take a good look, you have to use:

 view.measure(MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED), 
                MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED));

 view.layout(0, 0, view.getMeasuredWidth(), view.getMeasuredHeight()); 

I used the following main.xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  android:orientation="vertical"
   android:id="@+id/screen"
  android:layout_width="fill_parent"
  android:layout_height="fill_parent"
  >
<TextView
  android:layout_width="fill_parent"
  android:layout_height="wrap_content"
  android:text="@string/hello"
  />
<ImageView
  android:id="@+id/image"
  android:layout_width="fill_parent"
  android:layout_height="fill_parent"
/>
</LinearLayout>

The outcome is:

Reference