TypedArray.getText() 在 android.R.attr.text returns 空

Question

我正在尝试实现一个使用 StaticLayout 的自定义文本视图。为了获得视图的 'android:text' 属性，我在初始化字段中这样实现：

@SupressLint("ResourceType")
class ExampleTextView(context: Context, attrs: AttributeSet?, defStyleAttr: Int): View(...) {
    private var mText: String

    init {
        val styledAttributes = context.obtainStyledAttributes(attrs, intArrayOf(
            ...
            android.R.attr.text,
            ...
        ))

        mText = styledAttributes.getText(1)
        ...

        styledAttributes.recycle()
    }
    ...
}

然后在布局中xml:

<com.example.package.ExampleTextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="This is an example text" />

我显然在自定义文本视图中设置了 'android:text'。但是当我尝试从 TypedArray 获取属性时，它 return 为空。 styledAttributes.getString(1) 的另一次尝试也使 return 为空。

堆栈跟踪：

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.package, PID: 19154
    android.view.InflateException: Binary XML file line #10: Binary XML file line #10: Error inflating class com.example.package.ExampleTextView
    Caused by: android.view.InflateException: Binary XML file line #10: Error inflating class com.example.package.ExampleTextView
    Caused by: java.lang.reflect.InvocationTargetException
        at java.lang.reflect.Constructor.newInstance0(Native Method)
        at java.lang.reflect.Constructor.newInstance(Constructor.java:343)
        at android.view.LayoutInflater.createView(LayoutInflater.java:647)
        at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:790)
        at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:730)
        at android.view.LayoutInflater.rInflate(LayoutInflater.java:863)
        at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:824)
        at android.view.LayoutInflater.inflate(LayoutInflater.java:515)
        at android.view.LayoutInflater.inflate(LayoutInflater.java:423)
        at com.example.package.adapter.elementsAdapter.onCreateViewHolder(PatchNoteElementsAdapter.kt:54)
        at androidx.recyclerview.widget.RecyclerView$Adapter.createViewHolder(RecyclerView.java:7078)
        at androidx.recyclerview.widget.RecyclerView$Recycler.tryGetViewHolderForPositionByDeadline(RecyclerView.java:6235)
        at androidx.recyclerview.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:6118)
        at androidx.recyclerview.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:6114)
        at androidx.recyclerview.widget.LinearLayoutManager$LayoutState.next(LinearLayoutManager.java:2303)
        at androidx.recyclerview.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1627)
        at androidx.recyclerview.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1587)
        at androidx.recyclerview.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:665)
        at androidx.recyclerview.widget.RecyclerView.dispatchLayoutStep2(RecyclerView.java:4134)
        at androidx.recyclerview.widget.RecyclerView.dispatchLayout(RecyclerView.java:3851)
        at androidx.recyclerview.widget.RecyclerView.onLayout(RecyclerView.java:4404)
        at android.view.View.layout(View.java:20691)
        at android.view.ViewGroup.layout(ViewGroup.java:6194)
        at com.google.android.material.appbar.HeaderScrollingViewBehavior.layoutChild(HeaderScrollingViewBehavior.java:148)
        at com.google.android.material.appbar.ViewOffsetBehavior.onLayoutChild(ViewOffsetBehavior.java:43)
        at com.google.android.material.appbar.AppBarLayout$ScrollingViewBehavior.onLayoutChild(AppBarLayout.java:1996)
        at androidx.coordinatorlayout.widget.CoordinatorLayout.onLayout(CoordinatorLayout.java:918)
        at android.view.View.layout(View.java:20691)
        at android.view.ViewGroup.layout(ViewGroup.java:6194)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
        at android.view.View.layout(View.java:20691)
        at android.view.ViewGroup.layout(ViewGroup.java:6194)
        at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1812)
        at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1656)
        at android.widget.LinearLayout.onLayout(LinearLayout.java:1565)
        at android.view.View.layout(View.java:20691)
        at android.view.ViewGroup.layout(ViewGroup.java:6194)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
        at android.view.View.layout(View.java:20691)
        at android.view.ViewGroup.layout(ViewGroup.java:6194)
        at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1812)
        at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1656)
        at android.widget.LinearLayout.onLayout(LinearLayout.java:1565)
        at android.view.View.layout(View.java:20691)
        at android.view.ViewGroup.layout(ViewGroup.java:6194)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
E/AndroidRuntime:     at com.android.internal.policy.DecorView.onLayout(DecorView.java:765)
        at android.view.View.layout(View.java:20691)
        at android.view.ViewGroup.layout(ViewGroup.java:6194)
        at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:2806)
        at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2333)
        at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1473)
        at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:7215)
        at android.view.Choreographer$CallbackRecord.run(Choreographer.java:1004)
        at android.view.Choreographer.doCallbacks(Choreographer.java:816)
        at android.view.Choreographer.doFrame(Choreographer.java:751)
        at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:990)
        at android.os.Handler.handleCallback(Handler.java:873)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:280)
        at android.app.ActivityThread.main(ActivityThread.java:6706)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
     Caused by: kotlin.KotlinNullPointerException
        at com.example.package.ExampleTextView.<init>(ExampleTextView.kt:66)
        at com.example.package.ExampleTextView.<init>(ExampleTextView.kt:22)
            ... 67 more

有什么我遗漏的吗？

Answer 1

我导入了您的 TextView 并发现了与内部异常相同的异常

java.lang.NoSuchMethodException: <init> [class android.content.Context, interface android.util.AttributeSet]

我怀疑这与 attrs 的设置方式有关

通常当我扩展一个通用视图时，我会公开所有可用的构造函数，试一试。

class ExampleTextView: View {
    constructor(context: Context): super(context)
    constructor(context: Context, attrs: AttributeSet?): super(context, attrs) {
        this.attrs = attrs
    }
    constructor(context: Context, attrs: AttributeSet?, defStyleAttr: Int): super(context, attrs, defStyleAttr) {
        this.attrs = attrs
    }

    private var mText: String
    private var attrs: AttributeSet? = null

    init {
        val styledAttributes = context.obtainStyledAttributes(attrs, intArrayOf(android.R.attr.text))
        mText = styledAttributes.getText(1).toString()
        styledAttributes.recycle()
    }
}

Answer 2

简短回答：按升序对属性 ID 进行排序。

我找到了答案。这是因为在 context.obtainStyledAttributes().

上作为参数传递的 IntArray 的顺序

我在定义styledAttributes的时候是这样写的：

val styledAttributes = context.obtainStyledAttributes(attrs, intArrayOf(
    android.R.attr.fontFamily,
    android.R.attr.text,
    android.R.attr.textSize,
    android.R.attr.textColor,
    android.R.attr.textAlignment,
    android.R.attr.lineSpacingExtra
))

根据上文，styledAttributes 未排序。我们通过 android studio 文档 (Ctrl+Q) 查看常量值时就可以知道。等于：

val styledAttributes = context.obtainStyledAttributes(attrs, intArrayOf(
    16843692,
    16843087,
    16842901,
    16842904,
    16843697,
    16843287
))

虽然我没有在问题中提到，但当我尝试获取 textSize 和 lineSpacingExtra 的值时，我也得到了 null。

为什么？因为用无序列表调用 obtainStyledAttributes 时，无论你做什么，属性值都将为 null； getText(), getString(), getDimension(), getFont(), getResourceId(), 等等...如果属性常量的下一个值小于前一个。

这就是我尝试获取比以前小的属性常量16843087、16842901、16843287的值时得到空值的原因； 16843692, 16843087, 16843697.

此外，根据 Android 开发者参考，他们显然是说属性常量数组必须按升序排序。 https://developer.android.com/reference/android/content/res/Resources.Theme#obtainStyledAttributes(android.util.AttributeSet,%20int[],%20int,%20int)

attrs | int: The desired attributes in the style. These attribute IDs must be sorted in ascending order. This value cannot be null.

所以，为了正确获取属性值，我应该这样做：

val styledAttributes = context.obtainStyledAttributes(attrs, intArrayOf(
    android.R.attr.textSize,
    android.R.attr.textColor,
    android.R.attr.text,
    android.R.attr.lineSpacingExtra,
    android.R.attr.fontFamily,
    android.R.attr.textAlignment
))

升序排列的很好。希望这对未来的读者有所帮助。

TypedArray.getText() 在 android.R.attr.text returns 空

TypedArray.getText() on android.R.attr.text returns null

android

android-custom-view

typedarray