Dialog not displaying when calling from JNI

JNI调用Java显示对话框

最新推荐文章于 2021-12-11 15:55:32 发布

转载最新推荐文章于 2021-12-11 15:55:32 发布 · 1.7k 阅读

本文解决了一个问题：从JNI调用Java方法显示对话框时，对话框无法显示。原因是JNI回调不在UI线程中执行，导致对话框无法显示。解决方案是使用Handler确保在UI线程中调用对话框显示。

这是一篇非常有用的问答，将其复制到这里。

Dialog not displaying when calling from JNI

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I have a native C function (with JNI of course) that should callback a java method to display a dialog but this dialog is never displayed.

This is how this works:

C code calls a java method
The java method logs something
Then it calls showDialog(SOME_ID)
The onCreateDialog(SOME_ID) is called
The dialog is constructed using AlertDialog.Builder
When I call AlertDialog alert = builder.create() the application just stops right there (without crashing or freezing) but only when this call starts from the C code.

The code is as follows:

@Override
protected Dialog onCreateDialog(int id) {
    switch (id) {
    case SOME_ID:
        AlertDialog.Builder builder = new AlertDialog.Builder(this);
        builder.setMessage("Message");
        builder.setPositiveButton(...);
        builder.setNegativeButton(...);

        AlertDialog alert = builder.create();
        System.out.println("...Never called from JNI");
        return alert;
    }
    return null;
}

In 6 I mean that I log something before and after calling builder.create() but the log after the create method is never called so the method never returns and the dialog is never created. I have a button to trigger the dialog and, as expected, it works.

I did another test, I printed getApplicationContext() calling directly from onCreate() and from onCreateDialog() (called from C code) and it is the same, because one of the first things I thought was that the onCreateDialog() was being called from another Context or something.

Do you have any idea why the dialog is not displaying?

asked Feb 22 '11 at 15:58

licorna
734 5 15

1 Answer

active oldest votes

up vote 1 down vote accepted

The problem was that when calling back from JNI the application wasn't on UI Thread so the dialog was never shown. To fix it I used a Handler (on Activity):

public final Handler dialogHandler = new Handler(){     
    public void handleMessage(Message msg){
        showDialog(SOME_ID);
    }   
};

So instead of directly call showDialog() I do it by calling dialogHandler.sendMessage().

answered Feb 22 '11 at 23:57

licorna
734 5 15

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