kotlin中使用Java接口报错Parameter specified as non-null is null

简述

kotlin中使用Java接口，报错Parameter specified as non-null is null

问题

2021-07-06 09:33:35.053 2317-2317/com.lqbs.piot E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.lqbs.piot, PID: 2317
    java.lang.NullPointerException: Parameter specified as non-null is null: method kotlin.jvm.internal.Intrinsics.checkNotNullParameter, parameter hittingNode
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原因分析

有一个接口TreeViewControlListener.class

public interface TreeViewControlListener {
    int MIN_SCALE  = -1;
    int FREE_SCALE = 0;
    int MAX_SCALE  = 1;
    void onScaling(int state, int percent);
    void onDragMoveNodesHit(NodeModel<?> draggingNode,NodeModel<?> hittingNode,View draggingView,View hittingView);
}
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对应实现

binding!!.baseTreeView.setTreeViewControlListener(object : TreeViewControlListener {
            override fun onScaling(state: Int, percent: Int) {
				...
            }

            override fun onDragMoveNodesHit(
                draggingNode: NodeModel<*>,
                hittingNode: NodeModel<*>,
                draggingView: View,
                hittingView: View
            ) {
               ...
            }
        })
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当在java中调用’onDragMoveNodesHit’方法传入null参数时，会crash。如下

if(listener!=null){
    listener.onDragMoveNodesHit(draggingNode,null,draggingView,null);
}
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解决方案

首先，在java接口中添加@Nullable注解，这样在自动生成Kotlin实现接口代码时，就会可空，所以改为如下

TreeViewControlListener.class

public interface TreeViewControlListener {
    int MIN_SCALE  = -1;
    int FREE_SCALE = 0;
    int MAX_SCALE  = 1;
    void onScaling(int state, int percent);
    void onDragMoveNodesHit(@Nullable NodeModel<?> draggingNode, @Nullable NodeModel<?> hittingNode, @Nullable View draggingView, @Nullable View hittingView);
}
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根据实际情况，实现接口代码，添加?表示可空

override fun onDragMoveNodesHit(
    draggingNode: NodeModel<*>?,
    hittingNode: NodeModel<*>?,
    draggingView: View?,
    hittingView: View?
) {
    ....
}
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