java.lang.ClassCastException: TintContextWrapper cannot be cast to Activity

• 问题：在View中对View的context进行强制转换为Activity，报错

2018-02-25 17:38:38 java.lang.ClassCastException: androidx.appcompat.widget.TintContextWrapper cannot be cast to BaseActivity
at com.xx.agent.yy.databinding.ActivityUploadQrCodeBinding._internalCallbackOnClick(ActivityUploadQrCodeBinding.java:313)
at android.databinding.generated.callback.OnClickListener.onClick(OnClickListener.java:11)
at android.view.View.performClick(View.java:4457)
at android.view.View$PerformClick.run(View.java:18496)
at android.os.Handler.handleCallback(Handler.java:733)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5291)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:849)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:665)
at dalvik.system.NativeStart.main(Native Method)

• 原因：AppCompat类型的View会对传递进来的Context进行TintContextWrapper.wrap(context)包装，如下所示

public class AppCompatImageView extends ImageView implements TintableBackgroundView,
        TintableImageSourceView {
    
    

	....
	
    public AppCompatImageView(
            @NonNull Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
    
    
        super(TintContextWrapper.wrap(context), attrs, defStyleAttr);

        ThemeUtils.checkAppCompatTheme(this, getContext());

        mBackgroundTintHelper = new AppCompatBackgroundHelper(this);
        mBackgroundTintHelper.loadFromAttributes(attrs, defStyleAttr);

        mImageHelper = new AppCompatImageHelper(this);
        mImageHelper.loadFromAttributes(attrs, defStyleAttr);
    }
}

TintContextWrapper继承自ContextWrapper，调用wrap包装会将context传递到ContextWrapper的mBase中。所以将View的context强制转换为Activity就会报错。详细可看TintContextWrapper强转Activity失败原因深度探索

要想拿到真正的context，可以使用

    private fun getActivity(): Activity? {
    
    
        var mContext = context
        while (mContext is ContextWrapper){
    
    
            if (mContext is Activity){
    
    
                return mContext
            }
            mContext = (context as? ContextWrapper)?.baseContext
        }
        return null
    }