java - 带有按钮的 Android Eclipse 弹出消息

Question

我想通过点击一个按钮，弹出一条消息。

现在，只要我打开应用程序，就会出现弹出窗口。

顺便说一句，我想触发弹出窗口的按钮是 main.xml 中的关于按钮

这是我的 main.xml(带有布局内容):

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/main"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:background="#3DE400"
    android:orientation="vertical" >

    <!-- background originally #d78a00 -->

    <TextView
        android:id="@+id/title"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="60dp"
        android:fontFamily="sans-serif-condensed"
        android:paddingLeft="10dp"
        android:text="Sample App"
        android:textColor="#FFF"
        android:textSize="60sp" />

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:fontFamily="sans-serif-condensed"
        android:paddingLeft="10dp"
        android:text="@string/creator"
        android:textColor="#FFF"
        android:textSize="20dp" />

    <Button
        android:id="@+id/about"
        android:layout_width="123dp"
        android:layout_height="wrap_content"
        android:layout_marginTop="50dp"
        android:background="@android:color/transparent"
        android:fontFamily="sans-serif-condensed"
        android:gravity="left"
        android:paddingLeft="10dp"
        android:text="@string/about"
        android:textColor="#FFF"
        android:textSize="40dp"
        android:onClick="show" />

</LinearLayout>

这是我的 MainActivity.java:

package com.pranavsanghvi.sampleappv4;

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


public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        AlertDialog.Builder alert = new AlertDialog.Builder(MainActivity.this);
        alert.setTitle("About");
        alert.setMessage("Sample About");
        alert.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
            public void onClick (DialogInterface dialog, int id) {
                Toast.makeText (MainActivity.this, "Success", Toast.LENGTH_SHORT) .show();
            }
        });
        alert.setNegativeButton("No", new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int id) {
                Toast.makeText(MainActivity.this, "Fail", Toast.LENGTH_SHORT) .show();
            }
        });
        alert.show();


    }   
    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

}

Answer 1

首先，在 MainActivity 中声明您的警报和按钮:

public class Mainactivity extends Activity {
    private AlertDialog.Builder alert;
    private Button btAbout;

    //rest of the code
}

然后，在 onCreate() 中，像您一样创建警报，除了这一行:

alert.show();    // <--- remove this line as not to show the alert immediately

因为您已经声明了全局警报，请记住还要在此处删除 AlertDialog.Builder，而不是:

AlertDialog.Builder alert = new AlertDialog.Builder(MainActivity.this);
alert.setTitle("About");

//rest of the code

你应该有:

alert = new AlertDialog.Builder(MainActivity.this);
alert.setTitle("About");

//rest of the code

接下来，获取“关于”按钮的句柄:

btAbout = (Button) findViewById(R.id.about);

将 onClickListener 设置为按钮:

btAbout.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View view) {
        //when this button is clicked, show the alert
        alert.show();
    }
});

所有这些都在 onCreate() 中。现在，当单击按钮时，将显示您的警报。