java - 无法将 Java 代码转换为 Kotlin 以实现 OnChangeListener

Question

我有这段代码来为 Range Bar 库 实现监听器:

rangebar.setOnRangeBarChangeListener(new RangeBar.OnRangeBarChangeListener() {
        @Override
        public void onRangeChangeListener(RangeBar rangeBar, int leftPinIndex,
                                          int rightPinIndex, String leftPinValue, String rightPinValue) {
        }

    });

现在我尝试通过以下方式将其导入并更改为 kotlin:

rangebar.setOnRangeBarChangeListener(object: RangeBar.OnRangeBarChangeListener {
        override fun onRangeChangeListener(rangeBar:RangeBar, leftPinIndex:Int,
                                  rightPinIndex:Int, leftPinValue:String, rightPinValue:String) {
            textView.text = "$leftPinIndex"
        }
    })

或

rangebar.setOnRangeBarChangeListener { rangeBar, leftPinIndex, 
rightPinIndex, leftPinValue, rightPinValue -> 
textView.text = "$leftPinIndex" }

在这两种情况下，应用都会崩溃并出现以下错误:

java.lang.NullPointerException: Attempt to invoke virtual method 'void com.appyvet.materialrangebar.RangeBar.setOnRangeBarChangeListener> (com.appyvet.materialrangebar.RangeBar$OnRangeBarChangeListener)' on a null object reference

我做错了什么？

Answer 1

你的rangebar是null，

为避免崩溃，请像这样使用:

rangebar?.setOnRangeBarChangeListener(object: RangeBar.OnRangeBarChangeListener {
    override fun onRangeChangeListener(rangeBar:RangeBar, leftPinIndex:Int, rightPinIndex:Int, leftPinValue:String, rightPinValue:String) {
        textView.text = "$leftPinIndex"
    }
})

或

rangebar?.setOnRangeBarChangeListener { rangeBar, leftPinIndex, rightPinIndex, leftPinValue, rightPinValue -> 
    textView.text = "$leftPinIndex" 
}