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

协同程序会很好地做到这一点

CoroutineScope(Job() + Dispatchers.Main).launch {
                        Toast.makeText(context, "yourmessage",Toast.LENGTH_LONG).show()}

其他回答

Toast.makeText()只能从Main/UI线程调用。loop . getmainlooper()帮助你实现它:

JAVA

new Handler(Looper.getMainLooper()).post(new Runnable() {
    @Override
    public void run() {
        // write your code here
    }
});

科特林

Handler(Looper.getMainLooper()).post {
        // write your code here
}

这种方法的优点是您可以在没有活动或上下文的情况下运行UI代码。

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();
                }
            }
        );
    }

}

首先调用loop .prepare(),然后调用Toast.makeText().show()最后调用loop .loop():

Looper.prepare() // to be able to make toast
Toast.makeText(context, "not connected", Toast.LENGTH_LONG).show()
Looper.loop()

要在线程中显示对话框或烤面包机,最简洁的方法是使用Activity对象。

例如:

new Thread(new Runnable() {
    @Override
    public void run() {
        myActivity.runOnUiThread(new Runnable() {
            public void run() {
                myActivity.this.processingWaitDialog = new ProgressDialog(myActivity.this.getContext());
                myActivity.this.processingWaitDialog.setProgressStyle(ProgressDialog.STYLE_SPINNER);
                myActivity.this.processingWaitDialog.setMessage("abc");
                myActivity.this.processingWaitDialog.setIndeterminate(true);
                myActivity.this.processingWaitDialog.show();
            }
        });
        expenseClassify.serverPost(
                new AsyncOperationCallback() {
                    public void operationCompleted(Object sender) {
                        myActivity.runOnUiThread(new Runnable() {
                            public void run() {
                                if (myActivity.this.processingWaitDialog != null 
                                        && myActivity.this.processingWaitDialog.isShowing()) {
                                    myActivity.this.processingWaitDialog.dismiss();
                                    myActivity.this.processingWaitDialog = null;
                                }
                            }
                        }); // .runOnUiThread(new Runnable()
...

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);
      }
 });