我正在尝试用ListView项创建一个位图。我正在使用Greendroid库（如果这有任何区别）。我最初有这个工作的列表，其中＃项是＆lt; 7（因为你只能在屏幕上看到6个项目）。我现在尝试在获取绘图缓存之前单独构建每个视图项。在下面的代码中，我在childView.buildDrawingCache（）中得到一个空指针异常。我正确地调用了getView（）吗？这个问题还有其他简单的解决方案吗？
try {
Bitmap main = BitmapFactory.decodeResource(getResources(),R.drawable.dummy);
Bitmap dummy = BitmapFactory.decodeResource(getResources(),R.drawable.dummy);
Bitmap view;
Bitmap temp;
Canvas canvas = new Canvas();
Paint paint = new Paint();
Matrix matrix = new Matrix();
paint.setFilterBitmap(true);
File pic = new File(getFilesDir(),"txtabot.jpg");
//(ViewGroup) (getListView().getParent());
//((LinearLayout) getListView().getParent()).setDrawingCacheEnabled(true);
ListView lView = (ListView) getListView();
for (int i = 0; i<lView.getCount();i++) {
lView.setSelectionFromTop(i, 0);
View childView = adapter.getView(i, null ,lView );
childView.setDrawingCacheEnabled(true);
childView.buildDrawingCache(true);
view = childView.getDrawingCache().copy(Bitmap.Config.ARGB_8888, true);
//ItemView iView = ((ItemView)lView.getItemAtPosition(i));
//lView.getChildAt(i).setDrawingCacheEnabled(true);
//lView.getChildAt(i).buildDrawingCache(true);
//view = lView.getChildAt(i).getDrawingCache().copy(Bitmap.Config.ARGB_8888, true);
temp = Bitmap.createScaledBitmap(dummy, view.getWidth(), main.getHeight()+view.getHeight(), true);
temp = temp.copy(Bitmap.Config.ARGB_8888, true);
canvas.setBitmap(temp);
canvas.drawBitmap(main, matrix, paint);
//matrix.preTranslate(0, main.getHeight()-view.getHeight());
matrix.postTranslate(0, main.getHeight());
canvas.drawBitmap(view, matrix, paint);
matrix.reset();
main = temp.copy(Bitmap.Config.ARGB_8888, true);
}
//getListView().getChildAt(getListView().getCount());
//Bitmap main = getListView().getDrawingCache().copy(Bitmap.Config.ARGB_8888, true);
main.compress(Bitmap.CompressFormat.JPEG, 100, new FileOutputStream(pic));
Log.i("TAG", "ofter FOS.CLOSE()");
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
这是堆栈跟踪：
10-05 10:46:51.101: D/AndroidRuntime(16836): Shutting down VM
10-05 10:46:51.101: W/dalvikvm(16836): threadid=1: thread exiting with uncaught exception (group=0x40a481f8)
10-05 10:46:51.140: E/AndroidRuntime(16836): FATAL EXCEPTION: main
10-05 10:46:51.140: E/AndroidRuntime(16836): java.lang.NullPointerException
10-05 10:46:51.140: E/AndroidRuntime(16836): at com.gigabites.smsbot.LogActivity.onHandleActionBarItemClick(LogActivity.java:153)
10-05 10:46:51.140: E/AndroidRuntime(16836): at greendroid.app.GDActivity$1.onActionBarItemClicked(GDActivity.java:387)
10-05 10:46:51.140: E/AndroidRuntime(16836): at greendroid.widget.ActionBar$1.onClick(ActionBar.java:396)
10-05 10:46:51.140: E/AndroidRuntime(16836): at android.view.View.performClick(View.java:3511)
10-05 10:46:51.140: E/AndroidRuntime(16836): at android.view.View$PerformClick.run(View.java:14105)
10-05 10:46:51.140: E/AndroidRuntime(16836): at android.os.Handler.handleCallback(Handler.java:605)
10-05 10:46:51.140: E/AndroidRuntime(16836): at android.os.Handler.dispatchMessage(Handler.java:92)
10-05 10:46:51.140: E/AndroidRuntime(16836): at android.os.Looper.loop(Looper.java:137)
10-05 10:46:51.140: E/AndroidRuntime(16836): at android.app.ActivityThread.main(ActivityThread.java:4575)
10-05 10:46:51.140: E/AndroidRuntime(16836): at java.lang.reflect.Method.invokeNative(Native Method)
10-05 10:46:51.140: E/AndroidRuntime(16836): at java.lang.reflect.Method.invoke(Method.java:511)
10-05 10:46:51.140: E/AndroidRuntime(16836): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
10-05 10:46:51.140: E/AndroidRuntime(16836): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
10-05 10:46:51.140: E/AndroidRuntime(16836): at dalvik.system.NativeStart.main(Native Method)
10-05 10:46:51.710: I/dalvikvm(16836): threadid=3: reacting to signal 3
10-05 10:46:51.718: I/dalvikvm(16836): Wrote stack traces to '/data/anr/traces.txt'
10-05 10:46:52.226: I/dalvikvm(16836): threadid=3: reacting to signal 3
10-05 10:46:52.230: I/dalvikvm(16836): Wrote stack traces to '/data/anr/traces.txt'
10-05 10:46:52.726: I/dalvikvm(16836): threadid=3: reacting to signal 3
10-05 10:46:52.730: I/dalvikvm(16836): Wrote stack traces to '/data/anr/traces.txt'
10-05 10:46:53.230: I/dalvikvm(16836): threadid=3: reacting to signal 3
10-05 10:46:53.230: I/dalvikvm(16836): Wrote stack traces to '/data/anr/traces.txt'
10-05 10:46:53.730: I/dalvikvm(16836): threadid=3: reacting to signal 3
10-05 10:46:53.753: I/dalvikvm(16836): Wrote stack traces to '/data/anr/traces.txt'
10-05 10:46:54.238: I/dalvikvm(16836): threadid=3: reacting to signal 3
10-05 10:46:54.253: I/dalvikvm(16836): Wrote stack traces to '/data/anr/traces.txt'
10-05 10:46:54.730: I/dalvikvm(16836): threadid=3: reacting to signal 3
10-05 10:46:54.738: I/dalvikvm(16836): Wrote stack traces to '/data/anr/traces.txt'
10-05 10:46:55.230: I/dalvikvm(16836): threadid=3: reacting to signal 3
10-05 10:46:55.234: I/dalvikvm(16836): Wrote stack traces to '/data/anr/traces.txt'
10-05 10:46:55.742: I/dalvikvm(16836): threadid=3: reacting to signal 3
10-05 10:46:55.742: I/dalvikvm(16836): Wrote stack traces to '/data/anr/traces.txt'
10-05 10:46:56.234: I/dalvikvm(16836): threadid=3: reacting to signal 3
10-05 10:46:56.238: I/dalvikvm(16836): Wrote stack traces to '/data/anr/traces.txt'
10-05 10:46:57.074: I/dalvikvm(16836): threadid=3: reacting to signal 3
10-05 10:46:57.082: I/dalvikvm(16836): Wrote stack traces to '/data/anr/traces.txt'
10-05 10:46:57.238: I/dalvikvm(16836): threadid=3: reacting to signal 3
10-05 10:46:57.253: I/dalvikvm(16836): Wrote stack traces to '/data/anr/traces.txt'
10-05 10:46:57.738: I/dalvikvm(16836): threadid=3: reacting to signal 3
10-05 10:46:57.742: I/dalvikvm(16836): Wrote stack traces to '/data/anr/traces.txt'
10-05 10:46:58.250: I/dalvikvm(16836): threadid=3: reacting to signal 3
10-05 10:46:58.250: I/dalvikvm(16836): Wrote stack traces to '/data/anr/traces.txt'
10-05 10:46:58.750: I/dalvikvm(16836): threadid=3: reacting to signal 3
10-05 10:46:58.750: I/dalvikvm(16836): Wrote stack traces to '/data/anr/traces.txt'
10-05 10:46:59.238: I/dalvikvm(16836): threadid=3: reacting to signal 3
10-05 10:46:59.242: I/dalvikvm(16836): Wrote stack traces to '/data/anr/traces.txt'
10-05 10:46:59.746: I/dalvikvm(16836): threadid=3: reacting to signal 3
10-05 10:46:59.746: I/dalvikvm(16836): Wrote stack traces to '/data/anr/traces.txt'
10-05 10:47:00.246: I/dalvikvm(16836): threadid=3: reacting to signal 3
10-05 10:47:00.257: I/dalvikvm(16836): Wrote stack traces to '/data/anr/traces.txt'
10-05 10:47:00.742: I/dalvikvm(16836): threadid=3: reacting to signal 3
10-05 10:47:00.753: I/dalvikvm(16836): Wrote stack traces to '/data/anr/traces.txt'
10-05 10:47:01.582: I/dalvikvm(16836): threadid=3: reacting to signal 3
10-05 10:47:01.585: I/dalvikvm(16836): Wrote stack traces to '/data/anr/traces.txt'
10-05 10:47:02.105: I/dalvikvm(16836): threadid=3: reacting to signal 3
10-05 10:47:02.113: I/dalvikvm(16836): Wrote stack traces to '/data/anr/traces.txt'
更新：现在我正在给视图充气并将其绘制到画布（位图）并做同样的事情，但一切都有点奇怪。我真的不了解itemView.measure（）和itemView.layout方法。这是有效的代码：
try {
// Prepare Utilities
Bitmap main = BitmapFactory.decodeResource(getResources(),R.drawable.dummy);
Bitmap dummy = BitmapFactory.decodeResource(getResources(),R.drawable.dummy);
Bitmap view;
Bitmap temp;
//Canvas tempCanvas = new Canvas();
Canvas canvas = new Canvas();
Paint paint = new Paint();
Matrix matrix = new Matrix();
paint.setFilterBitmap(true);
File pic = new File(getFilesDir(),"txtabot.jpg");
final ListView lView = (ListView) getListView();
//for (int i = 0; i<lView.getChildCount();i++) {
for (int i = 0; i<3;i++) {
//View itemView = lView.getAdapter().getView(i, null, lView);
//itemView = lView.getChildAt(i);
//itemView.setDrawingCacheEnabled(true);
//itemView.draw(tempCanvas);
//final int viewheight = lView.getChildAt(lView.getFirstVisiblePosition()).getHeight();
View itemView = lView.getAdapter().getView(i, null, lView);
itemView.setLayoutParams(new LayoutParams(
LayoutParams.MATCH_PARENT, LayoutParams.WRAP_CONTENT));
itemView.measure(
MeasureSpec.getSize(itemView.getMeasuredWidth()),
MeasureSpec.getSize(itemView.getMeasuredHeight())
);
itemView.layout(0, 0,itemView.getMeasuredWidth() , itemView.getMeasuredHeight());
view = Bitmap.createScaledBitmap(dummy,itemView.getMeasuredWidth(),itemView.getMeasuredHeight(),true);
canvas.setBitmap(view);
itemView.draw(canvas);
//iew.setSelectionFromTop(i, 0);
//View itemView = lView.getChildAt(i);
//itemView.setDrawingCacheEnabled(true);
//view = itemView.getDrawingCache().copy(Bitmap.Config.ARGB_8888, true);
temp = Bitmap.createScaledBitmap(dummy, view.getWidth(), main.getHeight()+view.getHeight(), true);
//temp = temp.copy(Bitmap.Config.ARGB_4444, true);
canvas.setBitmap(temp);
canvas.drawBitmap(main, matrix, paint);
matrix.postTranslate(0, main.getHeight());
canvas.drawBitmap(view, matrix, paint);
matrix.reset();
main = temp.copy(Bitmap.Config.ARGB_8888, true);
}
main.compress(Bitmap.CompressFormat.JPEG, 100, new FileOutputStream(pic));
Log.i("TAG", "ofter FOS.CLOSE()");
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
它设法迭代列表项，但输出全部为黑色，带有一些可见的视图图标。