我有一个自定义ImageView，并且尝试在ImageView的getDrawable()方法中使用onDraw()。现在，这对于大多数设备和android版本似乎都可以正常工作，但是我现在开始在Google Pixel 2（Android 9）和其他一些运行Android 7.0的设备上收到 NullPointerException 。
有人知道为什么会这样吗？
public class CustomImageView extends android.support.v7.widget.AppCompatImageView {
...
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
Drawable drawable = getDrawable();
if (drawable == null)
throw new NullPointerException("drawable must not be null");
}
...
}
NPE 引发如下：
Fatal Exception: java.lang.NullPointerException: drawable must not be null
at de.simonmayrshofer.dfvafftrainer.imagemagnifier.ImageMagnifier.onDraw(ImageMagnifier.java:109)
at android.view.View.draw(View.java:20207)
at android.view.View.updateDisplayListIfDirty(View.java:19082)
at android.view.View.draw(View.java:19935)
at android.view.ViewGroup.drawChild(ViewGroup.java:4333)
at android.view.ViewGroup.dispatchDraw(ViewGroup.java:4112)
at android.view.View.draw(View.java:20210)
at android.view.View.updateDisplayListIfDirty(View.java:19082)
at android.view.View.draw(View.java:19935)
at android.view.ViewGroup.drawChild(ViewGroup.java:4333)
at android.view.ViewGroup.dispatchDraw(ViewGroup.java:4112)
at android.view.View.updateDisplayListIfDirty(View.java:19073)
at android.view.View.draw(View.java:19935)
at android.view.ViewGroup.drawChild(ViewGroup.java:4333)
at android.view.ViewGroup.dispatchDraw(ViewGroup.java:4112)
at android.view.View.draw(View.java:20210)
at android.widget.ScrollView.draw(ScrollView.java:1739)
at android.view.View.updateDisplayListIfDirty(View.java:19082)
at android.view.View.draw(View.java:19935)
at android.view.ViewGroup.drawChild(ViewGroup.java:4333)
at android.view.ViewGroup.dispatchDraw(ViewGroup.java:4112)
at android.view.View.updateDisplayListIfDirty(View.java:19073)
at android.view.View.draw(View.java:19935)
at android.view.ViewGroup.drawChild(ViewGroup.java:4333)
at android.view.ViewGroup.dispatchDraw(ViewGroup.java:4112)
at android.view.View.updateDisplayListIfDirty(View.java:19073)
at android.view.View.draw(View.java:19935)
at android.view.ViewGroup.drawChild(ViewGroup.java:4333)
at android.view.ViewGroup.dispatchDraw(ViewGroup.java:4112)
at android.view.View.updateDisplayListIfDirty(View.java:19073)
at android.view.View.draw(View.java:19935)
at android.view.ViewGroup.drawChild(ViewGroup.java:4333)
at android.view.ViewGroup.dispatchDraw(ViewGroup.java:4112)
at android.view.View.updateDisplayListIfDirty(View.java:19073)
at android.view.View.draw(View.java:19935)
at android.view.ViewGroup.drawChild(ViewGroup.java:4333)
at android.view.ViewGroup.dispatchDraw(ViewGroup.java:4112)
at android.view.View.updateDisplayListIfDirty(View.java:19073)
at android.view.View.draw(View.java:19935)
at android.view.ViewGroup.drawChild(ViewGroup.java:4333)
at android.view.ViewGroup.dispatchDraw(ViewGroup.java:4112)
at android.view.View.updateDisplayListIfDirty(View.java:19073)
at android.view.View.draw(View.java:19935)
at android.view.ViewGroup.drawChild(ViewGroup.java:4333)
at android.view.ViewGroup.dispatchDraw(ViewGroup.java:4112)
at android.view.View.updateDisplayListIfDirty(View.java:19073)
at android.view.View.draw(View.java:19935)
at android.view.ViewGroup.drawChild(ViewGroup.java:4333)
at android.view.ViewGroup.dispatchDraw(ViewGroup.java:4112)
at android.view.View.draw(View.java:20210)
at com.android.internal.policy.DecorView.draw(DecorView.java:780)
at android.view.View.updateDisplayListIfDirty(View.java:19082)
at android.view.ThreadedRenderer.updateViewTreeDisplayList(ThreadedRenderer.java:686)
at android.view.ThreadedRenderer.updateRootDisplayList(ThreadedRenderer.java:692)
at android.view.ThreadedRenderer.draw(ThreadedRenderer.java:801)
at android.view.ViewRootImpl.draw(ViewRootImpl.java:3312)
at android.view.ViewRootImpl.performDraw(ViewRootImpl.java:3116)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2485)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1460)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:7184)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:949)
at android.view.Choreographer.doCallbacks(Choreographer.java:761)
at android.view.Choreographer.doFrame(Choreographer.java:696)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:935)
at android.os.Handler.handleCallback(Handler.java:873)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Method.java)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
XML：
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent">
<ScrollView
android:id="@+id/xxx"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fillViewport="true">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:animateLayoutChanges="true"
android:gravity="bottom"
android:orientation="vertical">
<de.xxx.CustomImageView
android:id="@+id/xxx"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_margin="@dimen/fragment_margin"
android:adjustViewBounds="true"
android:scaleType="fitCenter"
android:src="someimage.png"
android:visibility="gone" />
</LinearLayout>
</ScrollView>
</RelativeLayout>
我正在使用Picasso将onCreateView()中的资产中的图像加载到ImageView中：
Picasso.with(getActivity()).load("file:///android_asset/img/abc.jpg".into(imageView);