Android Nougat：TextureView 不支持显示背景可绘制对象

我一直在我的Android应用程序中使用TextureView，并且它工作得很好。最近，我在使用 Android API 25 (7.1.2) 的 Android 设备上测试了我的代码。相同的代码现在不起作用并抛出错误，java.lang.UnsupportedOperationException: TextureView doesn't support displaying a background drawable.

我知道void setBackgroundDrawable (Drawable background)曾经是已弃用很长时间 https://developer.android.com/reference/android/view/TextureView.html，现在它一定已经被删除了。但我什至不是自己设置的。

我正在使用最新的 buildTools 和 SDK。所以，我想知道为什么textureView内部实现没有更新。

这是相关的堆栈跟踪：

java.lang.UnsupportedOperationException: TextureView doesn't support displaying a background drawable
at android.view.TextureView.setBackgroundDrawable(TextureView.java:315)
at android.view.View.setBackground(View.java:18124)
at android.view.View.<init>(View.java:4573)
at android.view.View.<init>(View.java:4082)
at android.view.TextureView.<init>(TextureView.java:159)
at com.abdulwasaetariq.xyz.ui.customView.AutoFitTextureView.<init>(AutoFitTextureView.java:24)
at com.abdulwasaetariq.xyz.ui.customView.AutoFitTextureView.<init>(AutoFitTextureView.java:20)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
[...]
at java.lang.Thread.run(Thread.java:745)

以下是我如何使用我的（尚未定制的）自定义TextureView：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.abdulwasaetariq.xyz.ui.activity.MainActivity">

    <com.abdulwasaetariq.xyz.ui.customView.AutoFitTextureView
        android:id="@+id/texture"
        android:layout_width="1080px"
        android:layout_height="1080px"
        android:layout_alignParentStart="true"
        android:layout_alignParentTop="true" />

</RelativeLayout>

这是我相关的 AutoFitTextureView.java： enter code here

public class AutoFitTextureView extends TextureView {

private int mRatioWidth = 0;
private int mRatioHeight = 0;

public AutoFitTextureView(Context context) {
    this(context, null);
}

public AutoFitTextureView(Context context, AttributeSet attrs) {
    this(context, attrs, 0); //(LINE#20)
}

public AutoFitTextureView(Context context, AttributeSet attrs, int defStyle) {
    super(context, attrs, defStyle); //(LINE#24)
}

public void setAspectRatio(int width, int height) {
    if (width < 0 || height < 0) {
        throw new IllegalArgumentException("Size cannot be negative.");
    }
    mRatioWidth = width;
    mRatioHeight = height;
    requestLayout();
}

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    int width = MeasureSpec.getSize(widthMeasureSpec);
    int height = MeasureSpec.getSize(heightMeasureSpec);
    if (0 == mRatioWidth || 0 == mRatioHeight) {
        setMeasuredDimension(width, height);
    } else {
        if (width < height * mRatioWidth / mRatioHeight) {
            setMeasuredDimension(width, width * mRatioHeight / mRatioWidth);
        } else {
            setMeasuredDimension(height * mRatioWidth / mRatioHeight, height);
        }
    }
}}

因此，如您所见，异常发生在super()方法，这意味着我的自定义TextureView不负责这个异常。这是内部电话。

这是我的 gradle 配置：

apply plugin: 'com.android.application'

android {
    compileSdkVersion 25
    buildToolsVersion '25.0.2'
    defaultConfig {
        applicationId "com.abdulwasaetariq.xyz"
        minSdkVersion 21
        targetSdkVersion 25
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    testCompile 'junit:junit:4.12'
    androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {
        exclude group: 'com.android.support', module: 'support-annotations'
        })
    compile 'com.android.support.constraint:constraint-layout:1.0.0-alpha8'
    compile 'com.github.hotchemi:permissionsdispatcher:2.3.2'
    annotationProcessor 'com.github.hotchemi:permissionsdispatcher-processor:2.3.2'
}

任何想法为什么会发生这种情况？ Android API 25 的任何发行说明中谈到了此更改吗？

以下是源代码片段View https://github.com/android/platform_frameworks_base/blob/nougat-cts-release/core/java/android/view/View.java对于 Android 牛轧糖：

/**
 * Allow setForeground/setBackground to be called (and ignored) on a textureview,
 * without throwing
 */
static boolean sTextureViewIgnoresDrawableSetters = false;

在单参数构造函数中（从所有其他构造函数调用）：

        // Prior to N, TextureView would silently ignore calls to setBackground/setForeground.
        // On N+, we throw, but that breaks compatibility with apps that use these methods.
        sTextureViewIgnoresDrawableSetters = targetSdkVersion <= M;

In the View抛出异常的构造函数：

...
        switch (attr) {
            case com.android.internal.R.styleable.View_background:
                background = a.getDrawable(attr);
                break;
...
    if (background != null) {
        setBackground(background);  // <--- this is the problematic line, apparently "background" is not null here
    }

的实际定义setBackground:

/**
 * Set the background to a given Drawable, or remove the background. If the
 * background has padding, this View's padding is set to the background's
 * padding. However, when a background is removed, this View's padding isn't
 * touched. If setting the padding is desired, please use
 * {@link #setPadding(int, int, int, int)}.
 *
 * @param background The Drawable to use as the background, or null to remove the
 *        background
 */
public void setBackground(Drawable background) {
    //noinspection deprecation
    setBackgroundDrawable(background);
}

然后覆盖setBackgroundDrawable in TextureView https://github.com/android/platform_frameworks_base/blob/nougat-cts-release/core/java/android/view/TextureView.java:

@Override
public void setBackgroundDrawable(Drawable background) {
    if (background != null && !sTextureViewIgnoresDrawableSetters) {
        throw new UnsupportedOperationException(
                "TextureView doesn't support displaying a background drawable");
    }
}

所以你可以从所有这些中拼凑出： 1) 你有一个目标 SDK N (Nougat) - 从你的构建文件中可以明显看出； 2）构造函数来自View确定非空背景（我目前无法解释这部分）。

这就是这成为一个实际问题所需要的全部。我没有看到你已经成功地在你的xml中定义了一个drawable，所以重写setBackground or setBackgroundDrawable对我来说似乎是解决这个问题的最明智的可能性。可能还有另一种解决方法（或者“建议的用法”可能是更好的术语），您可以设法强制background构造函数中的变量保持为空。