按钮单击Android上的事件

Question

This is going to be a real noob question, so please have mercy. I am trying to create a message box on a button click event in Android. I have read some examples on StackOverflow, but I can't seems to grasp the concept. In my main.xml file, I have defined the button xml as follows:

<Button
android:id="@+id/btnOK"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Display Message"
android:onClick="onBtnClicked" />

I read on one of the posts that I need to register the onClick event in the XML layout. So that is what I thought I did in the XML code above. Then, in my java code file, I have written the following code:

package com.example.helloandroid;

import android.app.Activity;
import android.content.DialogInterface;
import android.content.DialogInterface.OnClickListener;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;

public class HelloAndroid extends Activity 
{
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) 
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);        
    }   

    public void onBtnClicked(View v)
    { 
        if(v.getId() == R.id.btnOK)
        {
            MessageBox("Hello World");
        }       
    }

    public void MessageBox(String message)
    {
       Toast.makeText(this, message, Toast.LENGTH_SHORT);
    }   
}

To me, this makes sense. But the message box does not display when I click on the button. From the code imports above, you can see that I have already tried a few solutions without success. Am I perhaps missing a listener? I thought that the definition in the XML code would create this for me?

Thanks in advance :-)

Answer 1

Change

Toast.makeText(this, message, Toast.LENGTH_SHORT);

To

Toast.makeText(this, message, Toast.LENGTH_SHORT).show();

The show() makes sure you actually display the Toast, else you are only creating the Toast.

Answer 2

Toast.makeText(this, message, Toast.LENGTH_SHORT);

这是对的

Toast.makeText(this, message, Toast.LENGTH_SHORT).show();

Answer 3

Toast.makeText(this, message, Toast.LENGTH_SHORT).show(); - you need to call the show() method as now you are just creating the toast without showing it.

Answer 4

the Activity have to implement a View.OnClickListener, and implement the method onClick(View v)

in onCreate method, you have initialize the button (after the instruction setContentView):

Button b = (Button) findViewById(R.id.btnOK);
b.setOnClickListener(this);

in onClick method:

public void onClick(View v) {
    switch(v.getId()){
    case R.id.btnOK:
        /*  the instruccions of the button */
        break;
    }
}