java.lang.RuntimeException: Can‘t toast on a thread that has not called Looper.prepare()

拼搏现实的明天。 2023-09-26 09:28 1阅读 0赞

## 问题 ##

android 子线程中使用  
Toast.makeText(context, text, duration).show();，android studio 控制台报错

java.lang.RuntimeException: Can't toast on a thread that has not called Looper.prepare()

### 详细问题 ###

2022-09-25 09:50:24.746 20573-20830/com.example.electronicmall E/AndroidRuntime: FATAL EXCEPTION: OkHttp Dispatcher
        Process: com.example.electronicmall, PID: 20573
        java.lang.RuntimeException: Can't toast on a thread that has not called Looper.prepare()
            at android.widget.Toast$TN.<init>(Toast.java:474)
            at android.widget.Toast.<init>(Toast.java:142)
            at android.widget.Toast.makeText(Toast.java:333)
            at android.widget.Toast.makeText(Toast.java:323)
            at com.example.electronicmall.test.User.UserNewInfoActivity$10$1$1.onResponse(UserNewInfoActivity.java:483)
            at com.squareup.okhttp.Call$AsyncCall.execute(Call.java:168)
            at com.squareup.okhttp.internal.NamedRunnable.run(NamedRunnable.java:33)
            at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
            at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
            at java.lang.Thread.run(Thread.java:929)

### 解决方案 ###

对于Toast.makeText(context, text, duration).show();相关代码块，在具体逻辑执行前先调用Looper.prepare();再调用Toast.makeText().show();最后再调用Looper.loop();  
对于笔者而言  
原报错代码

intent = new Intent(UserSubInfoActivity.this, AllLoginActivity.class);//创建跳转到AllLoginActivity显示的窗口的Intent
    startActivity(intent);//进入album的窗口界面
    finish();
    Toast.makeText(UserSubInfoActivity.this, "退出应用", Toast.LENGTH_SHORT).show();

修改为

Looper.prepare();
    intent = new Intent(UserSubInfoActivity.this, AllLoginActivity.class);//创建跳转到AllLoginActivity显示的窗口的Intent
    startActivity(intent);//进入album的窗口界面
    finish();
    Toast.makeText(UserSubInfoActivity.this, "退出应用", Toast.LENGTH_SHORT).show(); 
    Looper.loop();

即可

### 原因 ###

由于非主线程中没有开启Looper（Android是不能直接在子线程中弹出Toast的），而Handler对象必须绑定Looper对象需要调用Looper.prepare()给线程创建消息循环，调用Looper.loop()使消息循环起作用。

### 参考文献 ###

[Can’t create handler inside thread Thread that has not called Looper.prepare()的解决][Can_t create handler inside thread Thread that has not called Looper.prepare]

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[Can_t create handler inside thread Thread that has not called Looper.prepare]: https://blog.csdn.net/weixin_42694582/article/details/81535083
[9cb4cb80a18345158f8a69e2f196e5b9.png]: https://img-blog.csdnimg.cn/9cb4cb80a18345158f8a69e2f196e5b9.png