Question

This is the line where i'm getting the error

Answer 1

您无法转换对象，因为它是不同的类型，例如，请使用以下代码：

public class Fruit {
    protected int size;

    public Fruit(int size) {
        this.size = size;
    }
}

public class Banana extends Fruit {

    private Color color;

    public Banana(int size, Color color) {
        super(size);
        this.color = color;
    }
}

public class Main {

    public static void main(String[] args) {
        Fruit someFruit = new Fruit(5);
        Banana yellowNanner = new Banana(3, Color.YELLOW);
        Fruit greenBanana = new Banana(4, Color.GREEN);            

        // Allowed cast because Banana is a fruit (extends it, no need to explicitly cast) [1]
        Fruit generalBanana = yellowNanner;

        // Allowed cast because The fruit was a banana originally [2]
        Banana stillABanana = (Banana) greenBanana;

        // Disallowed cast because Fruit isn't necessarily a banana [3]
        Banana notABanana = (Banana) someFruit; // gives a runtime exception (ClassCastException)

        // Disallowed cast, String isn't related to fruit [4]
        Fruit definitelynotfruit = (Fruit) "Pretend to be fruit"; // gives a runtime exception, and probably a compiler one too
    }
}

我想说的是你正在施展一些无法施展的东西。检查你试图强制转换的东西是否是超类或与它来自的类相同的级别。

您遇到的情况可能是[3]或[4]

但是从https://developer.android.com/reference/android/view/View.html判断：并且：https://developer.android.com/reference/android/widget/RelativeLayout.html

RelativeLayout是View的子类。 android.support.constraint.Constraintlayout是View

的子类

but a android.support.constraint.Constraintlayout can't be cast to a RelativeLayout

你基本上要做的是

RelativeLayout relativeLayout = (RelativeLayout) constraintLayout;

其中RelativeLayout不是constraintLayout的超类。

Answer 2

在xml文件中检查您的relativelayout的ID。似乎ID rootlayout属于constraint layout。在xml文件中更改相对布局的id。

或将您的rootlayout声明改为

ContraintLayout rootlayout = (ConstraintLayout) findViewById(R.id.rootlayout);

如何为Relativelayout修复此转换错误

2 个答案: