尝试在空对象引用上调用虚拟方法 'void com.parse.ParseImageView.setParseFile(com.parse.ParseFile)'

Question

我知道 NullPointerException 是什么，好吗？但是，这行代码可能有哪些错误：

mealImage.setParseFile(campaign.getImage());

给我一个NullPointerException?

 java.lang.NullPointerException: Attempt to invoke virtual method 'void com.parse.ParseImageView.setParseFile(com.parse.ParseFile)' on a null object reference
                                                                                 at com.alibdeir.signupactivity.mainAdapter.getItemView(mainAdapter.java:41)
                                                                                 at com.alibdeir.signupactivity.mainAdapter.getItemView(mainAdapter.java:19)
                                                                                 at com.parse.ParseQueryAdapter.getView(ParseQueryAdapter.java:606)
                                                                                 at android.widget.AbsListView.obtainView(AbsListView.java:2823)
                                                                                 at android.widget.ListView.measureHeightOfChildren(ListView.java:1290)
                                                                                 at android.widget.ListView.onMeasure(ListView.java:1202)
                                                                                 at android.view.View.measure(View.java:18580)
                                                                                 at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:728)
                                                                                 at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:464)
                                                                                 at android.view.View.measure(View.java:18580)
                                                                                 at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:728)
                                                                                 at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:464)
                                                                                 at android.view.View.measure(View.java:18580)
                                                                                 at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5827)
                                                                                 at android.widget.FrameLayout.onMeasure(FrameLayout.java:430)
                                                                                 at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:135)
                                                                                 at android.view.View.measure(View.java:18580)
                                                                                 at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5827)
                                                                                 at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1435)
                                                                                 at android.widget.LinearLayout.measureVertical(LinearLayout.java:721)
                                                                                 at android.widget.LinearLayout.onMeasure(LinearLayout.java:612)
                                                                                 at android.view.View.measure(View.java:18580)
                                                                                 at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5827)
                                                                                 at android.widget.FrameLayout.onMeasure(FrameLayout.java:430)
                                                                                 at android.view.View.measure(View.java:18580)
                                                                                 at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5827)
                                                                                 at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1435)
                                                                                 at android.widget.LinearLayout.measureVertical(LinearLayout.java:721)
                                                                                 at android.widget.LinearLayout.onMeasure(LinearLayout.java:612)
                                                                                 at android.view.View.measure(View.java:18580)
                                                                                 at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5827)
                                                                                 at android.widget.FrameLayout.onMeasure(FrameLayout.java:430)
                                                                                 at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2897)
                                                                                 at android.view.View.measure(View.java:18580)
                                                                                 at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2248)
                                                                                 at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1306)
                                                                                 at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1548)
                                                                                 at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1191)
                                                                                 at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6642)
                                                                                 at android.view.Choreographer$CallbackRecord.run(Choreographer.java:777)
                                                                                 at android.view.Choreographer.doCallbacks(Choreographer.java:590)
                                                                                 at android.view.Choreographer.doFrame(Choreographer.java:560)
                                                                                 at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:763)
                                                                                 at android.os.Handler.handleCallback(Handler.java:739)
                                                                                 at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                                 at android.os.Looper.loop(Looper.java:145)
                                                                                 at android.app.ActivityThread.main(ActivityThread.java:5942)
                                                                                 at java.lang.reflect.Method.invoke(Native Method)
                                                                                 at java.lang.reflect.Method.invoke(Method.java:372)
                                                                                 at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1389)
                                                                                 at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1184)

第41行：是我给你的第一行代码。第 19 行是：

public class mainAdapter extends ParseQueryAdapter<Campaign> {

那么，什么可以为空？我的 ParseImageView 是正确的，正确的 class 和列名。我如何获得图像： Campaign.class:

@ParseClassName("Campaign")

public class Campaign extends ParseObject {
    public Campaign() {
        // default Constructor
    }

    public String getTitle() {
        return getString("Title");
    }

    public String getDescription(){
        return getString("Description");
    }

    public ParseUser getAuthor() {
        return getParseUser("Owner");
    }

    public ParseFile getImage(){
        return getParseFile("Picture");
    }



}

需要更多信息？ 注意：不要-1冲我，我知道什么是NullPointerException。所以，注意！ 编辑：

<?xml version="1.0" encoding="utf-8"?>
<TableLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >
    <TableRow>
        <com.parse.ParseImageView
            android:id="@android:id/icon"
            android:layout_width="100dp"
            android:layout_height="100dp"
            />
        <TextView
            android:id="@+id/title"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textSize="20sp"
            android:textColor="#000000"
            />
        <TextView
            android:id="@+id/description"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textSize="10sp"
            android:textColor="#454343"
            />

    </TableRow>
</TableLayout>

getItemView():

   @Override
public View getItemView(Campaign campaign, View v, ViewGroup parent) {

    if (v == null) {
        v = View.inflate(getContext(), R.layout.list_single,null);
    }

    super.getItemView(campaign, v, parent);

    ParseImageView mealImage = (ParseImageView) v.findViewById(R.id.icon);
    ParseFile photoFile = campaign.getImage();
    if (photoFile != null) {
        mealImage.setParseFile(campaign.getImage());
        mealImage.loadInBackground(new GetDataCallback() {
            @Override
            public void done(byte[] data, ParseException e) {
                // nothing to do
            }
        });
    }

    TextView titleTextView = (TextView) v.findViewById(R.id.title);
    titleTextView.setText(campaign.getTitle());
    TextView descriptionTextView = (TextView) v
            .findViewById(R.id.description);
    descriptionTextView.setText(campaign.getDescription());
    return v;

}

编辑： 这不是重复的，我知道 nullPointerException 是什么。但我不明白什么是空的。我曾经使用 mParseQueryAdapter.setImageKey("Picture") 并且有效

Answer 1

当您尝试 findViewById 如果未找到引用视图，则它 returns null。

您将 android:id/icon 和创建一个新的 @+id/icon 搞混了。

这是您的代码：

 ParseImageView mealImage = (ParseImageView) v.findViewById(R.id.icon);

 <com.parse.ParseImageView
        android:id="@android:id/icon"
        android:layout_width="100dp"
        android:layout_height="100dp"
        />

改变

v.findViewById(R.id.icon);

到这个

v.findViewById(android.R.id.icon);

或相反（在你的 xml）
改变

android:id="@android:id/icon"

到

android:id="@+id/icon"

在幕后 Android 会将这些 ID 更改为数字让我们说：

android:id/icon = 123 和 +id/icon = 456

因此

<View
  android:id="android:id/icon"
  ... />

和

<View
  android:id="android:id/icon"
  ... />

将解析为两个不同的数字（意思是当你想要另一个时查找一个会给你 NullPointerException）

尝试在空对象引用上调用虚拟方法 'void com.parse.ParseImageView.setParseFile(com.parse.ParseFile)'

Attempt to invoke virtual method 'void com.parse.ParseImageView.setParseFile(com.parse.ParseFile)' on a null object reference

java

android

nullpointerexception

parse-platform

android-parsequeryadapter