大四实习准备2_java异常处理_android控件练习

2015-4-24

Java 异常处理

可以有多个catch;ArrayIndexOutOfBoundsException类是Exception类的子类RuntimeException类的一个间接子类;finally{}一定被执行;

异常分类：

1>继承关系

Object类->Throwable类->Error类(通常是硬件运行错误，通常不能通过程序来修改)(未捕获异常)、Exception类

Exception类->RuntimeException类(若不进行异常处理，可能编译时没问题，运行时就出错了)(未捕获异常)、其他类(捕获异常)。

2>

捕获异常(即 “必须处理异常”，通常由外部因素造成。可能出现该类异常而不try-catch 或者 不可能出现该类异常而try-catch，都会报错)。

未捕获异常

;

抛出异常(不立即处理异常，而是向上抛出异常，直到有地方处理为止)

 public class test{
     public static void main(String[] args) {
         try{
             test t = new test();
             t.a();
         }catch(Exception e){
                        //在这里处理异常
             System.out.println("processd in main()");
         }
     }
     private void a(){
         b();
     }
     private void b(){
         int[] r = new int[5];
         r[5]=10;//在这里发生异常
     }
 }        

或者 (?)使用throw、throws。

;

自定义异常

 //继承自Exception，写了两个构造函数。可以参考Exception类的代码
 class myException extends Exception{
     public myException() {
         // TODO Auto-generated constructor stub
     }
     public myException(String s){
         super(s);
     }
 }

 public class test{
     //定义一个可能发生自定义异常的方法
     public String yiChang(int x) throws myException{
         if( x>0 ){
             return "Right";
         }
         else{
             throw new myException("Negavite");
         }
     }
     public static void main(String[] args){
         test t1 = new test();

         try{
             System.out.println(t1.yiChang(5));
         }catch(myException e){
             System.out.println("异常信息为："+e.getMessage());
         }

         try{
             System.out.println(t1.yiChang(-2));
         }catch(myException e){
             System.out.println("异常信息为："+e.getMessage());
             //关注这些方法e.getMessage(),e.toString(),e.printStackTrace()
         }
     }
 }

自定义异常示例

android 控件练习UIBestPractice

 package com.example.uibestpractice;

 import java.util.ArrayList;

 import android.app.Activity;
 import android.os.Bundle;
 import android.view.Menu;
 import android.view.MenuItem;
 import android.view.View;
 import android.view.View.OnClickListener;
 import android.widget.Button;
 import android.widget.EditText;
 import android.widget.ListView;
 import android.widget.TextView;

 public class MainActivity extends Activity {
     ArrayList<talk> list = new ArrayList<talk>();
     ListView lv;
     EditText et;
     Button bt;
     talkAdapter adapter;
     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_main);
         inittalk();
         adapter = new talkAdapter(MainActivity.this, R.layout.diy_left_right, list);
         lv = (ListView) findViewById(R.id.listview);
         lv.setAdapter(adapter);
         et = (EditText) findViewById(R.id.edittext);
         bt = (Button) findViewById(R.id.button);
         bt.setOnClickListener(new OnClickListener() {

             @Override
             public void onClick(View view) {
                 // TODO Auto-generated method stub
                 String content = et.getText().toString();
                 if( !content.equals("") ){
                     talk t = new talk(content,talk.TYPE_SEND);
                     list.add(t);
                     adapter.notifyDataSetChanged();//当有新消息是，刷新ListView的显示
                     lv.setSelection(list.size());//将ListView定位到最后一行
                     et.setText(""+list.size());//清空输入框中的内容
                 }
             }
         });
     }
     private void inittalk() {
          //TODO Auto-generated method stub
         talk t = new talk("hello kiwi",talk.TYPE_RECEIVED);
         list.add(t);
         t = new talk("hello tryonce",talk.TYPE_SEND);
         list.add(t);
         t = new talk("Come on together",talk.TYPE_RECEIVED);
         list.add(t);
         t = new talk("It's my honor,my dearling",talk.TYPE_SEND);
         list.add(t);
     }
 }

MainActivity.java

 package com.example.uibestpractice;

 public class talk {
     public static final int TYPE_RECEIVED = 0;
     public static final int TYPE_SEND = 1;
     private String s;
     private int type;
     public talk(String s,int type){
         this.s = s;
         this.type = type;
     }
     public String getContent(){
         return s;
     }
     public int getType(){
         return type;
     }
 }

talk.java ListView的数据类

 package com.example.uibestpractice;

 import java.util.List;

 import android.content.Context;
 import android.view.LayoutInflater;
 import android.view.View;
 import android.view.ViewGroup;
 import android.webkit.WebView.FindListener;
 import android.widget.ArrayAdapter;
 import android.widget.TextView;

 public class talkAdapter extends ArrayAdapter<talk>{
     private int resourceId;

     public talkAdapter(Context context, int resource, List<talk> objects) {
         // TODO Auto-generated constructor stub
         super(context,resource,objects);
         this.resourceId = resource;
     }

     @Override
     public View getView(int position, View convertView, ViewGroup parent) {
         // TODO Auto-generated method stub
         talk t = getItem(position);
         View v;
         TextView tv;
         if( null == convertView ){
             v = LayoutInflater.from(getContext()).inflate(resourceId, null);
         }
         else{
             v = convertView;
         }

         if( t.getType() == t.TYPE_RECEIVED )    {
             tv = (TextView) v.findViewById(R.id.left_msg);
             v.findViewById(R.id.right_layout).setVisibility(View.GONE);
         }
         else{
             tv = (TextView) v.findViewById(R.id.right_msg);
             v.findViewById(R.id.left_layout).setVisibility(View.GONE);
         }
         tv.setText(t.getContent());
         return v;
     }
 }

talkAdapter.java 为ListView自定义的适配器

 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:tools="http://schemas.android.com/tools"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
     android:orientation="vertical"
      >
     <ListView
         android:id="@+id/listview"
         android:layout_width="match_parent"
         android:layout_height="0dp"
         android:layout_weight="1"
         android:divider="#0000"
         >
     </ListView>
     <LinearLayout
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:orientation="horizontal"
         >
         <TextView
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:text="input:"
             />
         <EditText
             android:id="@+id/edittext"
             android:layout_height="wrap_content"
             android:layout_width="0dp"
             android:layout_weight="1"
             android:hint="Type something......."
             android:maxLines="2"
             />
         <Button
             android:id="@+id/button"
             android:layout_height="wrap_content"
             android:layout_width="wrap_content"
             android:text="send"
             />

     </LinearLayout>
 </LinearLayout>

activity_main.xml 聊天窗口

 <?xml version="1.0" encoding="utf-8"?>
 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
     android:orientation="vertical" >
     <LinearLayout
         android:id="@+id/left_layout"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
         android:layout_gravity="left"
         android:background="@drawable/left">

         <TextView
             android:id="@+id/left_msg"
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:layout_gravity="center"
             android:layout_margin="10dp"
             android:textColor="#fff"
             />
      </LinearLayout>

         <LinearLayout
         android:id="@+id/right_layout"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
         android:layout_gravity="right"
         android:background="@drawable/right">

         <TextView
             android:id="@+id/right_msg"
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:layout_gravity="center"
             android:layout_margin="10dp"
             />
      </LinearLayout>

 </LinearLayout>

diy_left_right.xml 为ListView自定义的布局

问题：

MainActivity里

 lv.setSelection(list.size());//将ListView定位到最后一行 

觉得效果不对。(?)确实定位在新的数据那里了，但是原先的数据(除了第一条)都没了。