问题描述：
在安卓中，ui更新必须在主线执行，Toast是一种用于在屏幕上短暂显示消息的机制，它依赖主线程来进行创建和显示消息。当我们在子线程中直接调用Toast时，就会触发Can‘t create handler inside thread that has not called Looper报错。这个错误时由于Toast内部使用了Handler来处理消息队列，并在主线程中显示Toast，而在子线程中没有默认的Looper对象可供Handler使用。
当我们调用Toast的show方法时，会通过enqueueToast方法将toast插入消息队列中。
public void show() {if (Compatibility.isChangeEnabled(CHANGE_TEXT_TOASTS_IN_THE_SYSTEM)) {checkState(mNextView != null || mText != null, "You must either set a text or a view");} else {if (mNextView == null) {throw new RuntimeException("setView must have been called");}}INotificationManager service = getService();String pkg = mContext.getOpPackageName();TN tn = mTN;tn.mNextView = mNextView;final int displayId = mContext.getDisplayId();try {if (Compatibility.isChangeEnabled(CHANGE_TEXT_TOASTS_IN_THE_SYSTEM)) {if (mNextView != null) {// It's a custom toastservice.enqueueToast(pkg, mToken, tn, mDuration, displayId);} else {// It's a text toastITransientNotificationCallback callback =new CallbackBinder(mCallbacks, mHandler);service.enqueueTextToast(pkg, mToken, mText, mDuration, displayId, callback);}} else {service.enqueueToast(pkg, mToken, tn, mDuration, displayId);}} catch (RemoteException e) {// Empty}}
解决方案
新建一个Handler，用于子线程中使用Toast。
public class HandlerUtil {private static Handler mHandler;public static void init() {mHandler = new Handler();}public static void post(MyFunction func) {if (mHandler != null) {mHandler.removeCallbacksAndMessages(null);mHandler.post(new Runnable() {@Overridepublic void run() {func.apply();}});}}@FunctionalInterfacepublic interface MyFunction {void apply();}
}
在application中调用初始化
HandlerUtil.init();
在子线程中实现Toast。
HandlerUtil.post(()-> ToastUtil.showToast("test", 2000));
ToastUtil类可参考：安卓Toast避免重复显示
