不能将ClassCastException查看组$LayoutParams转换为ViewPager$LayoutParams

Question

我的初始代码行在重写的方法onGlobalLayout()中。

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

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

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，如其他帖子所示：

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

您的图像已经有布局参数。与其用新对象替换它们(在本例中是错误类型的对象，ViewPager希望它们是ViewPager.LayoutParams)，您可以修改现有的布局参数，如下所示：

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

注意，无条件地请求onGlobalLayout()中的重新布局可能是个坏主意，会导致无限的布局传递。我自己还没有核实是否是这样的。

Answer 2

这样做

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

更新

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

Answer 3

您应该确保您使用的LayoutParam类来自正确的父布局类。您需要将LayoutParams的ViewGroup设置为ViewPager所处的位置，作为需要知道分配给子视图的大小的View的父级。例如，在您的示例中，ViewGroup是一个RelativeLayout，您需要使用RelativeLayout.LayoutParams类。

您可以尝试如下：

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