AlertDialog and ProgressDialog 的用法

  AlertDialog是对话框的一种，这个对话框是置顶于所有界面元素之上 的，能够屏蔽掉其他控件的交互能力，所以常用来提示一些警告信息。

比如为了防止用户误删重要内容，在删除前弹出一个确认对话框。下面就开始学习它的用法：

 

  首先在一个空白的主Layout里面添加一个button，这是为了弹出对话框。

 activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
app:layout_behavior="@string/appbar_scrolling_view_behavior"
tools:context="com.example.jwg.helloworld.SecondActivity"
tools:showIn="@layout/activity_second">

<Button
    android:id="@+id/btn2"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="btn2" />
</RelativeLayout>

然后就可以MainActivity里面java的代码了。

MainActivity.xml

package com.example.jwg.helloworld;

import android.content.DialogInterface;
import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.util.Log;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;
import android.view.Window;
import android.widget.Button;
import android.widget.ProgressBar;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity implements View.OnClickListener {
protected ProgressBar progressBar;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        setContentView(R.layout.activity_main);
        Log.e("Hello World", "onCreate: ");
        progressBar = (ProgressBar) findViewById(R.id.progressbar);
        Button btn =(Button)findViewById(R.id.btn);
        btn.setOnClickListener(this);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "This is Button", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).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.menu_main, menu);
        return true;
    }
    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        switch (item.getItemId()) {
            case R.id.add:
                Toast.makeText(this, "Click add", Toast.LENGTH_SHORT).show();
                break;
            case R.id.remove:
                Toast.makeText(this, "Click remove",Toast.LENGTH_SHORT).show();
        }
        return true;
    }
    @Override
    public void onClick(View v) {
        switch (v.getId()){
            case  R.id.btn:
                AlertDialog.Builder dialog = new AlertDialog.Builder(MainActivity.this);
                dialog.setTitle("This is Dialog");
                dialog.setMessage("Something important");
                dialog.setCancelable(false);
                dialog.setPositiveButton("ok", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                    }
                });
                dialog.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {

                    }
                });
                dialog.show();
                break;
            default:
                break;
        }

    }
}
//                int progress = progressBar.getProgress();
//                progress = progress+50;
//                progressBar.setProgress(progress);/
//                if  (progressBar.getVisibility() == View.GONE){
//                    progressBar.setVisibility(View.VISIBLE);
//                }else{
//                    progressBar.setVisibility(View.GONE);
//                }  /
              

代码并不多其中有很多是多余的代码，主要的就是这点：

  @Override
    public void onClick(View v) {
        switch (v.getId()){
            case  R.id.btn:
                AlertDialog.Builder dialog = new AlertDialog.Builder(MainActivity.this);
                dialog.setTitle("This is Dialog");
                dialog.setMessage("Something important");
                dialog.setCancelable(false);
                dialog.setPositiveButton("ok", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                    }
                });
                dialog.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {

                    }
                });
                dialog.show();
                break;
            default:
                break;
        }

    }
}

       这个代码的其实就是这样的 ：

  首先通过 AlertDialog.Builder创建出一个 AlertDialog的实例，然后可以为这个对话框设 置标题、内容、可否取消等属性，

接下来调用 setPositiveButton()方法为对话框设置确定按钮 的点击事件，调用 setNegativeButton()方法设置取消按钮的

点击事件，最后调用 show()方法 将对话框显示出来。

 

  ProgressDialog 的用法请看下篇！