【发布时间】：2020-11-01 13:20:19
【问题描述】：
我在 Android Studio 中创建了一个自定义视图模板和一个继承自模板的自定义视图。如果我在自定义视图中访问一个方法，整个应用程序会在 Logcat 中崩溃并显示此错误消息：
2020-11-01 13:53:22.790 587-587/de.rescuemod E/AndroidRuntime: FATAL EXCEPTION: main
Process: de.rescuemod, PID: 587
java.lang.RuntimeException: Unable to start activity ComponentInfo{de.rescuemod/de.rescuemod.formulars.bike.FormBikeActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void de.rescuemod.customElements.MonoEditText.setText(java.lang.String)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2928)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3063)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1823)
at android.os.Handler.dispatchMessage(Handler.java:107)
at android.os.Looper.loop(Looper.java:198)
at android.app.ActivityThread.main(ActivityThread.java:6729)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:876)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void de.rescuemod.customElements.MonoEditText.setText(java.lang.String)' on a null object reference
at de.rescuemod.formulars.bike.FormBikeActivity.readDatabase(FormBikeActivity.kt:653)
at de.rescuemod.formulars.bike.FormBikeActivity.onCreate(FormBikeActivity.kt:598)
at android.app.Activity.performCreate(Activity.java:7136)
at android.app.Activity.performCreate(Activity.java:7127)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1272)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2908)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3063)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1823)
at android.os.Handler.dispatchMessage(Handler.java:107)
at android.os.Looper.loop(Looper.java:198)
at android.app.ActivityThread.main(ActivityThread.java:6729)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:876)
2020-11-01 13:53:22.824 587-587/? I/Process：发送信号。 PID：587 SIG：9
这是我的父自定义视图模板：
open class CustomElementTemplate(context : Context, attrs : AttributeSet) : ConstraintLayout(context, attrs) {
/* -------------------- Member variables -------------------- */
/** Main linear layout */
val llMain = LinearLayout(context)
/** Title textview */
val txtTitle = TextView(context)
/** Getting the density of the view */
val density = context.displayMetrics.density.toInt()
/* -------------------- Initialization -------------------- */
/**
* Primary Constructor
*/
init {
//Constraint layout
this.id = R.id.cl_customelementtemplate
setPadding(8 * density, 0, 8 * density, 0)
background = resources.getDrawable(R.drawable.border_padding, null)
layoutParams = LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.WRAP_CONTENT)
//Title of the view
txtTitle.id = R.id.txt_title
val lpTitle = LayoutParams(
LayoutParams.WRAP_CONTENT,
LayoutParams.WRAP_CONTENT
)
txtTitle.setBackgroundColor(if (getDarkMode(context)) {
resources.getColor(R.color.backgroundAccent_dark, null)
} else {
resources.getColor(R.color.backgroundAccent_light, null)
})
txtTitle.layoutParams = lpTitle
txtTitle.setPadding(5 * density, 0, 5 * density, 0)
txtTitle.textSize = 15f
txtTitle.setTextColor(Color.parseColor("#8A8A8A"))
txtTitle.visibility = View.GONE
addView(txtTitle)
//Main LinearLayout
llMain.id = R.id.ll_main
llMain.minimumHeight = 30 * density
llMain.orientation = LinearLayout.VERTICAL
llMain.layoutParams = LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.WRAP_CONTENT)
llMain.setPadding(8 * density, 20 * density, 8 * density, 14 * density)
addView(llMain)
}
/* -------------------- Lifecycle -------------------- */
/**
* After the layout was completly loaded in the view, execute the code here
*/
override fun onFinishInflate() {
super.onFinishInflate()
//Setting margins
val constraintSet = ConstraintSet()
constraintSet.clone(this)
constraintSet.connect(txtTitle.id, ConstraintSet.START, this.id, ConstraintSet.START,5 * density)
constraintSet.connect(txtTitle.id, ConstraintSet.TOP, this.id, ConstraintSet.TOP,0)
constraintSet.applyTo(this)
}
}
自定义视图：
class MonoEditText(context: Context, attrs : AttributeSet) : CustomElementTemplate(context, attrs) {
/* -------------------- Member variables -------------------- */
/** EditText element */
private var etxt = EditText(context)
/* -------------------- Initialization -------------------- */
/**
* Primary Constructor
*/
init {
//Collect the values from XML
context.theme.obtainStyledAttributes(attrs, R.styleable.MonoEditText, 0, 0).apply {
//EditText / AutocompleteText
if(getBoolean(R.styleable.MonoEditText_autoComplete, false)) {
etxt = AutoCompleteTextView(context)
}
etxt.id = R.id.etxt_main
etxt.layoutParams = LayoutParams(LayoutParams.MATCH_PARENT, 60 * density)
llMain.minimumHeight = 30 * density
llMain.addView(etxt)
//Fill all kind of textes like titles, subtitles, etc.
try {
if(getString(R.styleable.MonoEditText_title)?.isNotEmpty()!!) {
setTitle(getString(R.styleable.MonoEditText_title)!!)
}
} catch ( e: Exception) {}
//InputType
when(getString(R.styleable.MonoEditText_inputType)) {
"0" -> etxt.inputType = InputType.TYPE_NUMBER_FLAG_SIGNED or InputType.TYPE_CLASS_NUMBER or InputType.TYPE_NUMBER_FLAG_DECIMAL
"1" -> etxt.inputType = InputType.TYPE_CLASS_NUMBER
"2" -> etxt.inputType = InputType.TYPE_CLASS_TEXT
"3" -> etxt.inputType = InputType.TYPE_NUMBER_FLAG_DECIMAL
"4" -> etxt.inputType = InputType.TYPE_TEXT_FLAG_CAP_WORDS
"5" -> etxt.inputType = InputType.TYPE_TEXT_FLAG_CAP_CHARACTERS
}
}
}
/* -------------------- Getter/Setter Methods -------------------- */
/**
* Set the selected value by string
* @param value String which should be choosen
*/
fun setText(value : String) {
//etxt.setText(value)
}
}
我在 xml 活动中添加自定义视图，如下所示：
<de.rescuemod.customElements.MonoEditText
android:id="@+id/etxt_LGEW"
android:layout_width="match_parent"
android:layout_height="wrap_content"
app:inputType="number"
app:title="@string/LGEW" />
在活动中，我在editText字段中输入了一个值：
class FormularActivity : FormularTemplate() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
//Connection to the XML-Layout-File
setContentView(R.layout.activity_form_bike)
...
etxt_LGEW.setText("Leergewicht")
...
}
}
感谢您的帮助
【问题讨论】：
-
在你的最终代码 sn-p 中，
etxt_LGEW是null。 -
好的，我能做些什么呢？对于我要添加“findviewbyId”并将结果存储在变量中的每个自定义视图？还是有更好的解决方案？
-
您可以使用view binding、
findViewById()或类似的解决方案。这与这是一个自定义视图这一事实无关。 -
在早期版本中，我在自定义视图中使用了一个 XML，我使用“View.inflate()”将其添加到类中并且它起作用了。但是我想完全以编程方式编写它，从那时起，它就不再起作用了。而且我需要在每个活动中使用自定义视图 50-100 次，因此，我需要一种比在每个自定义视图中添加“findviewbyId”更智能的方法；）
-
如果你不使用 CommonsWare 的建议，你总是会得到一个 NPE。
标签： android kotlin android-custom-view