Android 使用自定义ImageView类，获取NullPointerException

我使用自定义的

ImageView

类使插入的图像适合屏幕的宽度，但保持纵横比。在我使用这个自定义的

ImageView

的所有其他地方，它似乎都能工作，但这一页不行。搞不懂/摸不着头脑。提前谢谢你

• 图像URL以JSON形式从服务器调用接收
• 图像加载了

  urlmageviewhelper

• 此ImageView与其他ImageView之间的唯一区别在于加载时使用自定义动画

自定义图像视图类

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（删除所有不必要的代码）

---

最初在

ImageView

中没有可绘制文件，因此

getDrawable（）

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);
    }
}

---

最初在

ImageView

中没有可绘制文件，因此

getDrawable（）

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);
    }
}

---

不完全确定，但我认为在第一次调用onMeasure时，您没有可绘制集。不完全确定，但我认为在第一次调用onMeasure时，您没有可绘制集。尝试了此操作，但获得了

java.lang.IllegalStateException:onMeasure（）未通过调用setMeasuredDimension（）设置测量的维度。

。而且不确定它为什么不起作用，因为使用此自定义图像视图的其他页面都采用相同的格式。@TheName Ok，更新了我的答案。在这种情况下，只需将其设置为0，就好像没有不重要的可绘制图形一样。您也可以将其设置为其他一些预定义值。尝试了此操作，但getting

java.lang.IllegalStateException:onMeasure（）没有通过调用setMeasuredDimension（）

来设置测量的维度。而且不确定它为什么不起作用，因为使用此自定义图像视图的其他页面都采用相同的格式。@TheName Ok，更新了我的答案。在这种情况下，只需将其设置为0，就好像没有不重要的可绘制图形一样。也可以将其设置为其他一些预定义值。

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)

@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);
    }
}