ClassCastException ViewGroup $ LayoutParams无法转换为ViewPager $ LayoutParams [英] ClassCastException ViewGroup$LayoutParams cannot be cast to ViewPager$LayoutParams

问题描述

我的初始代码行在覆盖的方法 onGlobalLayout（）内：

My initial code line is inside the overridden method onGlobalLayout():

img.setLayoutParams(new LayoutParams(LayoutParams.MATCH_PARENT, 100));

ClassCastException发生在重写的方法 onGlobalLayout（）-

ClassCastException occuring in the overridden method onGlobalLayout()-

错误日志：

09-02 14:25:35.326: E/AndroidRuntime(5187): java.lang.ClassCastException: android.view.ViewGroup$LayoutParams cannot be cast to android.support.v4.view.ViewPager$LayoutParams
09-02 14:25:35.326: E/AndroidRuntime(5187):     at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1319)
09-02 14:25:35.326: E/AndroidRuntime(5187):     at android.view.View.measure(View.java:15181)
09-02 14:25:35.326: E/AndroidRuntime(5187):     at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:617)
09-02 14:25:35.326: E/AndroidRuntime(5187):     at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:399)
09-02 14:25:35.326: E/AndroidRuntime(5187):     at android.view.View.measure(View.java:15181)
09-02 14:25:35.326: E/AndroidRuntime(5187):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4814)
09-02 14:25:35.326: E/AndroidRuntime(5187):     at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1390)

当我执行以下操作以解决上述错误时，如其他SO帖子所示：

And when I do the following in order to resolve the above error as indicated in other SO posts:

img.setLayoutParams(new ViewPager.LayoutParams(ViewPager.LayoutParams.MATCH_PARENT, 100));

然后，我得到编译时间错误：

Then, I get the compile time error:

The constructor ViewPager.LayoutParams(int, int) is undefined

xml中的

ViewPager定义如下：

ViewPager in xml is defined like:

<android.support.v4.view.ViewPager
 android:id="@+id/HView"
 android:layout_width="560dp"
 android:layout_height="255dp"
 android:layout_centerHorizontal="true"
 android:layout_marginLeft="160sp"
 android:layout_marginTop="110sp"
 android:layout_marginBottom="80sp">
 </android.support.v4.view.ViewPager>

推荐答案

您的图像已经具有布局参数。 ViewPager 希望将它们替换为 ViewPager.LayoutParams ），您可以像这样修改现有的布局参数：

Your image already has layout params. Instead of replacing them with a new object (which is of wrong type in this case, ViewPager expects them to be ViewPager.LayoutParams), you can modify existing layout params like this:

ViewGroup.LayoutParams params = img.getLayoutParams();
params.width = ViewGroup.LayoutParams.MATCH_PARENT;
params.height = 100;
img.requestLayout();

请注意，无条件地在 onGlobalLayout（）可能是一个坏主意，导致布局遍历无限。我还没有亲自验证是否是这种情况。

Note that unconditionally requesting re-layout in onGlobalLayout() can be a bad idea, leading to infinite layout passes. I haven't verified it myself whether this is the case.

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