ClassCastException ViewGroup $ LayoutParams无法强制转换为ViewPager $ LayoutParams

Question

我的初始代码行在重写方法中onGlobalLayout():

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

在重写方法中发生ClassCastException 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帖子中所示:

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

然后,我得到编译时错误:

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

xml中的ViewPager定义如下:

<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>

Answer 1

您的图片已经有布局参数.而不是用新对象替换它们(在这种情况下是错误的类型,ViewPager期望它们ViewPager.LayoutParams),你可以像这样修改现有的布局参数:

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

请注意,无条件请求重新布局onGlobalLayout()可能是一个坏主意,导致无限的布局传递.我自己没有验证是否是这种情况.