Javascript java.lang.RuntimeException:Can'；t在未调用Looper.prepare（）的线程上吐司

我正在按照Udemy的教程制作一个天气应用程序。这也是我第一次使用JSON数据，所以我不确定这是否会影响我的情况。然而，每次我运行我的应用程序时，它都会打开；当我按下按钮显示给定城市的天气时，应用程序崩溃

我研究了Looper.prepare（），因为它包含在错误中，但是添加Looper不起作用（我对编码是新手，可能做得不正确），我还尝试添加runOnUiThread（new Runnable），但没有任何效果（同样，我可能做得不正确）

---

应该在主线程上调用您的

Toast.makeText

方法。您可以这样做：

runOnUiThread(new Runnable() {
    public void run() {
        Toast.makeText(getApplicationContext(), "Could not find weather :(", Toast.LENGTH_SHORT).show();
    }
});

---

问题是因为您的toast正在doInBackground方法中创建和显示。在android中，用户界面操作必须在UI线程中处理。在UI线程中调用onPostExecute方法，但在另一个线程中调用doInBackground方法。要解决您的问题，请从doInBackground方法中删除Toast，并在onPostExecute方法中放入以下行：

//如果s等于null，doInBackground中会出现错误
如果（s==null）{
Toast.makeText（getApplicationContext（），“找不到天气：（”，
吐司。长度（短）。show（）；
}

见：

2019-09-11 13:24:52.431 
7574-7658/com.example.whatstheweather E/AndroidRuntime: FATAL EXCEPTION: 
AsyncTask #1

Process: com.example.whatstheweather, PID: 7574
java.lang.RuntimeException: An error occurred while executing 
doInBackground()
        at android.os.AsyncTask$4.done(AsyncTask.java:399)
        at 
    java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:383)
    at java.util.concurrent.FutureTask.setException(FutureTask.java:252)
    at java.util.concurrent.FutureTask.run(FutureTask.java:271)
    at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:289)       atjava.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167) atjava.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
    at java.lang.Thread.run(Thread.java:919)

Caused by: java.lang.RuntimeException: Can't toast on a thread that has 
not called Looper.prepare()
    at android.widget.Toast$TN.<init>(Toast.java:407)
    at android.widget.Toast.<init>(Toast.java:121)
    at android.widget.Toast.makeText(Toast.java:286)
    at android.widget.Toast.makeText(Toast.java:276)

atcom.example.whatstheweather.MainActivity$DownloadTask. 
doInBackground(MainActivity.java:81)
atcom.example.whatstheweather.MainActivity$DownloadTask. 
doInBackground(MainActivity.java:53)
    at android.os.AsyncTask$3.call(AsyncTask.java:378)
    at java.util.concurrent.FutureTask.run(FutureTask.java:266)
    at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:289) 
    atjava.util.concurrent.ThreadPoolExecutor. 
    runWorker(ThreadPoolExecutor.java:1167) 

atjava.util.concurrent.ThreadPoolExecutor$Worker. 
run(ThreadPoolExecutor.java:641) 
    at java.lang.Thread.run(Thread.java:919) 

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.whatstheweather, PID: 11228
    java.lang.IllegalStateException: Could not execute method for 
    android:onClick
    at 
androidx.appcompat.app.AppCompatViewInflater$DeclaredOnClickListener. 
onClick(AppCompatViewInflater.java:390)
    at android.view.View.performClick(View.java:7140)
    at android.view.View.performClickInternal(View.java:7117)
    at android.view.View.access$3500(View.java:801)
    at android.view.View$PerformClick.run(View.java:27351)
    at android.os.Handler.handleCallback(Handler.java:883)
    at android.os.Handler.dispatchMessage(Handler.java:100)
    at android.os.Looper.loop(Looper.java:214)
    at android.app.ActivityThread.main(ActivityThread.java:7356)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller. 
run(RuntimeInit.java:492)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
 Caused by: java.lang.reflect.InvocationTargetException
    at java.lang.reflect.Method.invoke(Native Method)
    at 
androidx.appcompat.app.AppCompatViewInflater$DeclaredOnClickListener. 
onClick(AppCompatViewInflater.java:385)
    at android.view.View.performClick(View.java:7140) 
    at android.view.View.performClickInternal(View.java:7117) 
    at android.view.View.access$3500(View.java:801) 
    at android.view.View$PerformClick.run(View.java:27351) 
    at android.os.Handler.handleCallback(Handler.java:883) 
    at android.os.Handler.dispatchMessage(Handler.java:100) 
    at android.os.Looper.loop(Looper.java:214) 
    at android.app.ActivityThread.main(ActivityThread.java:7356) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller. 
run(RuntimeInit.java:492) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930) 
 Caused by: java.lang.RuntimeException: Only one Looper may be created 
per thread
    at android.os.Looper.prepare(Looper.java:108)
    at android.os.Looper.prepare(Looper.java:103)
    at 
com.example.whatstheweather.MainActivity.getWeather(MainActivity.java:43)
    at java.lang.reflect.Method.invoke(Native Method) 
    at 
androidx.appcompat.app.AppCompatViewInflater$DeclaredOnClickListener. 
onClick(AppCompatViewInflater.java:385) 
    at android.view.View.performClick(View.java:7140) 
    at android.view.View.performClickInternal(View.java:7117) 
    at android.view.View.access$3500(View.java:801) 
    at android.view.View$PerformClick.run(View.java:27351) 
    at android.os.Handler.handleCallback(Handler.java:883) 
    at android.os.Handler.dispatchMessage(Handler.java:100) 
    at android.os.Looper.loop(Looper.java:214) 
    at android.app.ActivityThread.main(ActivityThread.java:7356) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller. 
run(RuntimeInit.java:492) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)

runOnUiThread(new Runnable() {
    public void run() {
        Toast.makeText(getApplicationContext(), "Could not find weather :(", Toast.LENGTH_SHORT).show();
    }
});