Android 11适配指南之Toast解析

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起源

在targetSdkVersion为30的情况下，在Android 11的小米10手机上运行，调用ToastUtil的时候闪退报错：

null cannot be cast to non-null type android.widget.LinearLayout 

且看已知条件：

• targetSdkVersion 30
• Android 11
• 小米10

文末附Android 11适配手册

定位问题

ok，遇到问题，迅速定位。我在原有的Toast调用上重新封装了一下，即ToastUtil。

所以很快就定位到问题所在了

 private fun createToast(msg: String) { if (toast == null) { toast = Toast.makeText(YUtils.getApp().applicationContext, msg, Toast.LENGTH_SHORT) } else { toast!!.setText(msg) } val linearLayout = toast!!.view as LinearLayout val messageTextView = linearLayout.getChildAt(0) as TextView messageTextView.textSize = 15f toast!!.show() } 

没错，就是这句进行了转换：

val linearLayout = toast!!.view as LinearLayout 

代码也比较简单，拿到view之后只是设置了一下字体大小。

为什么这么写呢，且看接下来源码分析（非常简单）。

源码解析

我们一般的调用是这么写的：

Toast.makeText(context, msg, Toast.LENGTH_SHORT).show() 

一行代码，也很容易能找到重点——makeText，没错，接下来从这里开始分析

compileSdkVersion 30之前

以compileSdkVersion 28为例，makeText源码：

 public static Toast makeText(@NonNull Context context, @Nullable Looper looper, @NonNull CharSequence text, @Duration int duration) { Toast result = new Toast(context, looper); LayoutInflater inflate = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE); View v = inflate.inflate(com.android.internal.R.layout.transient_notification, null); TextView tv = (TextView)v.findViewById(com.android.internal.R.id.message); tv.setText(text); result.mNextView = v; result.mDuration = duration; return result; } 

这几行的代码重点在哪呢，在这：

View v = inflate.inflate(com.android.internal.R.layout.transient_notification, null); 

引用了一个布局来显示信息

这个layout也非常的简单：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical" android:background="?android:attr/toastFrameBackground"> <TextView android:id="@android:id/message" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_weight="1" android:layout_marginHorizontal="24dp" android:layout_marginVertical="15dp" android:layout_gravity="center_horizontal" android:textAppearance="@style/TextAppearance.Toast" android:textColor="@color/primary_text_default_materiaal_light"/> </LinearLayout> 

根布局LinearLayout 和TextView显示文本。

所以才有了前面报错的这行代码：

val linearLayout = toast!!.view as LinearLayout 

现在看来其实是没有错的，事实上运行在Android11以下也确实没问题。

setView、getView也是没问题的

 / * Set the view to show. * @see #getView */ public void setView(View view) { mNextView = view; } / * Return the view. * @see #setView */ public View getView() { return mNextView; } 

author：yechaoa

compileSdkVersion 30之后

重点来了，在compileSdkVersion 30之后，源码是有改动的

还是直接看重点makeText：

 public static Toast makeText(@NonNull Context context, @Nullable Looper looper, @NonNull CharSequence text, @Duration int duration) { if (Compatibility.isChangeEnabled(CHANGE_TEXT_TOASTS_IN_THE_SYSTEM)) { Toast result = new Toast(context, looper); result.mText = text; result.mDuration = duration; return result; } else { Toast result = new Toast(context, looper); View v = ToastPresenter.getTextToastView(context, text); result.mNextView = v; result.mDuration = duration; return result; } } 

嗯？view的获取方式变了，原来是inflate的方式，现在是

View v = ToastPresenter.getTextToastView(context, text); 

ok，继续看ToastPresenter.getTextToastView

public class ToastPresenter { ... @VisibleForTesting public static final int TEXT_TOAST_LAYOUT = R.layout.transient_notification; / * Returns the default text toast view for message {@code text}. */ public static View getTextToastView(Context context, CharSequence text) { View view = LayoutInflater.from(context).inflate(TEXT_TOAST_LAYOUT, null); TextView textView = view.findViewById(com.android.internal.R.id.message); textView.setText(text); return view; } } 

到这里是不是有点熟悉了，没错，跟compileSdkVersion 28中的源码差不多，但是layout变成常量了，且有@VisibleForTesting注解，不过xml代码还是一样的。

而且setView、getView也弃用的

 / * Set the view to show. * * @see #getView * @deprecated Custom toast views are deprecated. Apps can create a standard text toast with the * {@link #makeText(Context, CharSequence, int)} method, or use a * <a href="{@docRoot}reference/com/google/android/material/snackbar/Snackbar">Snackbar</a> * when in the foreground. Starting from Android {@link Build.VERSION_CODES#R}, apps * targeting API level {@link Build.VERSION_CODES#R} or higher that are in the background * will not have custom toast views displayed. */ @Deprecated public void setView(View view) { mNextView = view; } / * Return the view. * * <p>Toasts constructed with {@link #Toast(Context)} that haven't called {@link #setView(View)} * with a non-{@code null} view will return {@code null} here. * * <p>Starting from Android {@link Build.VERSION_CODES#R}, in apps targeting API level {@link * Build.VERSION_CODES#R} or higher, toasts constructed with {@link #makeText(Context, * CharSequence, int)} or its variants will also return {@code null} here unless they had called * {@link #setView(View)} with a non-{@code null} view. If you want to be notified when the * toast is shown or hidden, use {@link #addCallback(Callback)}. * * @see #setView * @deprecated Custom toast views are deprecated. Apps can create a standard text toast with the * {@link #makeText(Context, CharSequence, int)} method, or use a * <a href="{@docRoot}reference/com/google/android/material/snackbar/Snackbar">Snackbar</a> * when in the foreground. Starting from Android {@link Build.VERSION_CODES#R}, apps * targeting API level {@link Build.VERSION_CODES#R} or higher that are in the background * will not have custom toast views displayed. */ @Deprecated @Nullable public View getView() { return mNextView; } 

直接来看注释的重点：

@deprecated Custom toast views are deprecated. Apps can create a standard text toast with the{@link #makeText(Context, CharSequence, int)} method, or use a <a href=”{@docRoot}reference/com/google/android/material/snackbar/Snackbar”>Snackbar</a>when in the foreground. Starting from Android {@link Build.VERSION_CODES#R}, appstargeting API level {@link Build.VERSION_CODES#R} or higher that are in the backgroundwill not have custom toast views displayed.

大意：自定义toast view已经弃用，你可以创建一个标准的toast，或者用Snackbar。从Android R开始，将不再显示自定位toast view。

Android R 也就是Android11，具体的版本对应关系查看

这里有同学可能会有一些想法，既然getView弃用了，那我可不可以像系统一样通过ToastPresenter.getTextToastView来获取呢，很遗憾，是不行的，ToastPresenter是@hide。。

适配方案

综上所诉，适配方案也了然于心了。

方案一

使用标准的toast

Toast.makeText(context, msg, Toast.LENGTH_SHORT).show() 

方案二

使用Snackbar

Snackbar的使用跟Toast差不多，更多查看这个。

Snackbar.make(view, "已加入行程", Snackbar.LENGTH_SHORT).show() 

方案三

不使用系统的toast，但可以借鉴来写一个自定义view

大致思路：

• 初始化引用自定义布局
• 编写一些公开的set、get属性
• 加上进入进出动画
• 开始/结束显示倒计时

等有空了再来补一下这个。。

Android 11开发手册

《Android 11 开发者手册》

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