如何使用Kotlin Android扩展与碎片?
如果我在onCreateView()中使用它们，我得到这个NullPointerException异常:
导致:java.lang.NullPointerException:试图调用virtual .lang. nullpointerexception
android.view.View. view. findviewbyid (int) `
空对象引用
下面是片段代码:
package com.obaied.testrun.Fragment
import android.os.Bundle
import android.support.v4.app.Fragment
import android.util.Log
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import com.obaied.acaan.R
import kotlinx.android.synthetic.main.fragment_card_selector.*
public class CardSelectorFragment : Fragment() {
val TAG = javaClass.canonicalName
companion object {
fun newInstance(): CardSelectorFragment {
return CardSelectorFragment()
}
}
override fun onCreateView(inflater: LayoutInflater?, container: ViewGroup?, savedInstanceState: Bundle?): View? {
var rootView = inflater?.inflate(R.layout.fragment_card_selector, container, false)
btn_K.setOnClickListener { Log.d(TAG, "onViewCreated(): hello world"); }
return rootView
}
}
`
在Fragments中，请在onActivityCreated中编写代码:-
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
super.onCreateView(inflater, container, savedInstanceState)
return inflater.inflate(R.layout.login_activity, container, false)
}
override fun onActivityCreated(savedInstanceState: Bundle?) {
super.onActivityCreated(savedInstanceState)
callbackManager = CallbackManager.Factory.create()
initialization()
onClickLogin()
onClickForgot()
onClickSocailLogIn()
}
由Kotlin Android Extensions插件生成的合成属性需要一个Fragment/Activity视图来预先设置。
在你的例子中，对于Fragment，你需要使用view。onViewCreated中的btn_K
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
super.onCreateView(inflater, container, savedInstanceState)
val view = inflater.inflate(R.layout.fragment_card_selector, container, false)
view.btn_K.setOnClickListener{} // access with `view`
return view
}
或者更好的是，你应该只访问onViewCreated中的合成属性
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
super.onCreateView(inflater, container, savedInstanceState)
return inflater.inflate(R.layout.fragment_card_selector, container, false)
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
btn_K.setOnClickListener{} // access without `view`
}
请注意savedInstanceState参数应该是空的Bundle?，同时勾选导入合成属性
为特定布局导入所有小部件属性非常方便
一口气:
进口kotlinx.android.synthetic.main。> <布局。*
因此，如果布局文件名是activity_main.xml，我们将导入
kotlinx.android.synthetic.main.activity_main。*。
如果我们想在View上调用合成属性，我们也应该这样做
进口kotlinx.android.synthetic.main.activity_main.view。*。
在Fragments中，请在onActivityCreated中编写代码:-
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
super.onCreateView(inflater, container, savedInstanceState)
return inflater.inflate(R.layout.login_activity, container, false)
}
override fun onActivityCreated(savedInstanceState: Bundle?) {
super.onActivityCreated(savedInstanceState)
callbackManager = CallbackManager.Factory.create()
initialization()
onClickLogin()
onClickForgot()
onClickSocailLogIn()
}
