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()
        }
    }
}

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);
    }
}

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;
    }
}

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;
    }
}

<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>

<?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>

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。