使用自定义ImageView类，获取NullPointerException

时间：2014-03-20 00:40:53

标签： android nullpointerexception imageview

我使用自定义ImageView类使插入的图像适合屏幕宽度，但保持纵横比。它似乎适用于我使用此自定义ImageView的所有其他地方，但不是这一页。无法弄明白/刮擦头。提前谢谢！

  • 图像URL通过服务器调用
    • 以JSON格式接收
  • 图片已加载UrlImageViewHelper
  • 此ImageView与其他ImageView之间的唯一区别是它在加载时使用自定义动画

自定义ImageView类 

public class AspectRatioImageView extends ImageView {

public AspectRatioImageView(Context context) {
    super(context);
}

public AspectRatioImageView(Context context, AttributeSet attrs) {
    super(context, attrs);
}

public AspectRatioImageView(Context context, AttributeSet attrs, int defStyle) {
    super(context, attrs, defStyle);
}

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    int width = MeasureSpec.getSize(widthMeasureSpec);
    int height = width * getDrawable().getIntrinsicHeight() / getDrawable().getIntrinsicWidth();
    setMeasuredDimension(width, height);
}

}

包含ImageView的片段（剪下所有不必要的代码） 

public class MainFragment extends Fragment {

private AspectRatioImageView rateMember;

static MainFragment newInstance() {
    MainFragment fragment = new MainFragment();
    return fragment;
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment_main, container, false);

    rateMember = (AspectRatioImageView) view.findViewById(R.id.rate_picture);

    rateMember.setOnClickListener(new OnClickListener() {
        @Override
        public void onClick(View view) {
            FragmentManager fm = getFragmentManager();
            FragmentTransaction ft = fm.beginTransaction();
            ViewMemberFragment fragment = ViewMemberFragment.newInstance(picId);
            ft.replace(R.id.fragment_container, fragment);
            ft.addToBackStack(null);
            ft.commit();
        }
    });

    if (GlobalMethods.isNetworkAvailable(getActivity())) { new GetRandomMemberTask().execute(); }
    else { Toast.makeText(getActivity(), R.string.no_internet, Toast.LENGTH_SHORT).show(); }

    return view;
}

private class GetRandomMemberTask extends AsyncTask<Void, Void, Void> {

    protected void onPreExecute() {
        btnVoteDown.setVisibility(View.GONE);
        btnVoteUp.setVisibility(View.GONE);
        btnNextPic.setVisibility(View.GONE);
    }

    protected Void doInBackground(Void... params) {
        JSONWriter writer = new JSONWriter(getActivity());
        writer.createJsonForGetPic(0);

        HttpPostRequest post = new HttpPostRequest(getActivity());
        post.createPost(HttpPostRequest.GET_PIC_URL);
        post.addJSON(JSONWriter.FILENAME_GET_PIC);
        String jsonString = post.sendPostReturnJson();

        JSONReader reader = new JSONReader(getActivity());
        member = reader.getMemberObject(jsonString);

        return null;
    }

    protected void onPostExecute(Void result) {
        super.onPostExecute(result);
        caption.setText(member.getCaption());
        UrlImageViewHelper.setUrlDrawable(rateMember, member.getImageUrl(), R.drawable.image_placeholder,
                new UrlImageViewCallback() {
                    @Override
                    public void onLoaded(ImageView arg0, Bitmap arg1, String arg2, boolean arg3) {
                        Animation popIn = AnimationUtils.loadAnimation(getActivity(), R.anim.pop_in);
                        rateMember.startAnimation(popIn);
                    }
        });
        picId = member.getPicId();
        if (hasAlreadyVoted()) { 
            btnNextPic.setVisibility(View.VISIBLE);
        }
        else {
            btnVoteDown.setVisibility(View.VISIBLE);
            btnVoteUp.setVisibility(View.VISIBLE);
        }
        return;
    }
}

}

XML 

<?xml version="1.0" encoding="utf-8"?>
<ScrollView
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#fff" >

<LinearLayout 
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical" >

    <FrameLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="20dp" >

        <com.walintukai.derpteam.AspectRatioImageView
            android:id="@+id/rate_picture"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:contentDescription="@string/desc_rate_image" />

        <RelativeLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_gravity="bottom"
            android:paddingTop="4dp"
            android:paddingBottom="4dp"
            android:orientation="horizontal"
            android:background="@drawable/transparent_gradient_footer" >

            <ImageView
                android:id="@+id/btn_vote_up"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginLeft="80dp"
                android:layout_alignParentLeft="true"
                android:visibility="gone"
                android:src="@drawable/arrow_up"
                android:contentDescription="@string/desc_vote_up" />

            <ImageView
                android:id="@+id/btn_vote_down"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginRight="80dp"
                android:layout_alignParentRight="true"
                android:visibility="gone"
                android:src="@drawable/arrow_down"
                android:contentDescription="@string/desc_vote_down" />

            <ImageView
                android:id="@+id/btn_next_pic"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_centerHorizontal="true"
                android:visibility="gone"
                android:src="@drawable/arrow_next"
                android:contentDescription="@string/desc_next_picture" />

        </RelativeLayout>

    </FrameLayout>

    <com.walintukai.derpteam.CustomFontBoldTextView
        android:id="@+id/caption"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="4dp"
        android:gravity="center_horizontal"
        android:textAppearance="@style/caption" />

</LinearLayout>

</ScrollView>

堆栈跟踪 

03-19 17:31:49.341: E/AndroidRuntime(13652): FATAL EXCEPTION: main
03-19 17:31:49.341: E/AndroidRuntime(13652): java.lang.NullPointerException
03-19 17:31:49.341: E/AndroidRuntime(13652):    at com.walintukai.derpteam.AspectRatioImageView.onMeasure(AspectRatioImageView.java:24)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at android.view.View.measure(View.java:15395)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4826)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at android.view.View.measure(View.java:15395)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4826)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1396)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at android.widget.LinearLayout.measureVertical(LinearLayout.java:681)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at android.widget.LinearLayout.onMeasure(LinearLayout.java:574)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at android.view.View.measure(View.java:15395)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at android.widget.ScrollView.measureChildWithMargins(ScrollView.java:1456)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at android.widget.ScrollView.onMeasure(ScrollView.java:387)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at android.view.View.measure(View.java:15395)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4826)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1396)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at android.widget.LinearLayout.measureVertical(LinearLayout.java:681)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at android.widget.LinearLayout.onMeasure(LinearLayout.java:574)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at android.view.View.measure(View.java:15395)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at android.widget.LinearLayout.measureVertical(LinearLayout.java:833)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at android.widget.LinearLayout.onMeasure(LinearLayout.java:574)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at android.view.View.measure(View.java:15395)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4826)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at android.view.View.measure(View.java:15395)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at android.widget.LinearLayout.measureVertical(LinearLayout.java:833)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at android.widget.LinearLayout.onMeasure(LinearLayout.java:574)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at android.view.View.measure(View.java:15395)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4826)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2362)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at android.view.View.measure(View.java:15395)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1985)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1226)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1399)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1119)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:4553)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at android.view.Choreographer$CallbackRecord.run(Choreographer.java:725)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at android.view.Choreographer.doCallbacks(Choreographer.java:555)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at android.view.Choreographer.doFrame(Choreographer.java:525)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:711)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at android.os.Handler.handleCallback(Handler.java:615)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at android.os.Handler.dispatchMessage(Handler.java:92)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at android.os.Looper.loop(Looper.java:137)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at android.app.ActivityThread.main(ActivityThread.java:4950)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at java.lang.reflect.Method.invokeNative(Native Method)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at java.lang.reflect.Method.invoke(Method.java:511)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1004)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:771)
03-19 17:31:49.341: E/AndroidRuntime(13652):    at dalvik.system.NativeStart.main(Native Method)

1 个答案:

答案 0 :(得分：5)

您最初的ImageView内没有抽奖，因此getDrawable()会返回null。

您可以将代码更改为：

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    if (getDrawable() != null {
        int width = MeasureSpec.getSize(widthMeasureSpec);  
        int height = width * getDrawable().getIntrinsicHeight() / getDrawable().getIntrinsicWidth();
        setMeasuredDimension(width, height);
    } else {
        setMeasuredDimension(0, 0);
    }
}
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