下面的异常是什么意思;我该怎么解决呢?

这是代码:

Toast toast = Toast.makeText(mContext, "Something", Toast.LENGTH_SHORT);

这是例外:

java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
     at android.os.Handler.<init>(Handler.java:121)
     at android.widget.Toast.<init>(Toast.java:68)
     at android.widget.Toast.makeText(Toast.java:231)

当前回答

 runOnUiThread(new Runnable() {
            public void run() {
                Toast.makeText(mContext, "Message", Toast.LENGTH_SHORT).show();
            }
        });

其他回答

你需要从UI线程调用Toast.makeText(…):

activity.runOnUiThread(new Runnable() {
  public void run() {
    Toast.makeText(activity, "Hello", Toast.LENGTH_SHORT).show();
  }
});

这是从另一个(复制)SO答案复制粘贴。

在执行以下操作之前,我一直得到这个错误。

public void somethingHappened(final Context context)
{
    Handler handler = new Handler(Looper.getMainLooper());
    handler.post(
        new Runnable()
        {
            @Override
            public void run()
            {
                Toast.makeText(context, "Something happened.", Toast.LENGTH_SHORT).show();
            }
        }
    );
}

并把它变成一个单例类:

public enum Toaster {
    INSTANCE;

    private final Handler handler = new Handler(Looper.getMainLooper());

    public void postMessage(final String message) {
        handler.post(
            new Runnable() {
                @Override
                public void run() {
                    Toast.makeText(ApplicationHolder.INSTANCE.getCustomApplication(), message, Toast.LENGTH_SHORT)
                        .show();
                }
            }
        );
    }

}

这是因为Toast.makeText()是从工作线程调用的。它应该像这样从主UI线程调用

runOnUiThread(new Runnable() {
      public void run() {
        Toast toast = Toast.makeText(mContext, "Something", Toast.LENGTH_SHORT);
      }
 });

Rxjava和RxAndroid用户:

public static void shortToast(String msg) {
    Observable.just(msg)
            .observeOn(AndroidSchedulers.mainThread())
            .subscribe(message -> {
                Toast.makeText(App.getInstance(), message, Toast.LENGTH_SHORT).show();
            });
}

这通常发生在从任何后台线程调用主线程上的某些内容时。让我们看一个例子。

private class MyTask extends AsyncTask<Void, Void, Void> {


@Override
protected Void doInBackground(Void... voids) {
        textView.setText("Any Text");
        return null;
    }
}

在上面的例子中,我们通过doInBackground()方法在主UI线程中的textview上设置文本,该方法只在工作线程上操作。