Android零碎知识（一）

public abstract Resources getResources ()

Return a Resources instance for your application's package.

BitmapFactory
extends Object

java.lang.Object 
   ↳ android.graphics.BitmapFactory 

Class Overview

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Creates Bitmap objects from various sources, including files, streams, and byte-arrays. 

public void translate (float dx, float dy) 
Added in API level 1
Preconcat the current matrix with the specified translation



When working with matrices, the word concatenation refers to multiplication.

Since matrix multiplication is not commutative, there is a separate word for backwards multiplication.
Pre-concatenating a to b means setting a = b × a. (As opposed to a = a × b, which will give a different matrix)

The canvas maintains a matrix and the canvas is manipulated by methods which are well defined in OpenGL

 三种列表对话框：setItems，setItems，setMultiChoiceItems。

在 接口DialogInterface.OnClickListener的抽象方法

public abstract void onClick (DialogInterface dialog, int which) 中的参数which：The button that was clicked (e.g. BUTTON1)
or the position of the item clicked

既能监听列表项（>=0）,又能监听按钮（<=0)

BUTTON_NEGATIVE=-2，BUTTON_NEUTRAL=-3，BUTTON_POSITIVE=-1；

public AlertDialog.Builder setSingleChoiceItems (CharSequence[] items, int checkedItem, DialogInterface.OnClickListener listener)

其中参数checkedItem  specifies which item is checked. If -1 no items are checked.因为有默认选项，onclick方法若不点击列表项，这个默认值就获取不到，所以在onclick方法里需要设置index的默认值为1。下面的程序是在构造方法传入1的。

另外注意在多选列表对话框中是如何获得用户选择的列表项，先得到对话框的Listview对象，扫描的方式

 

package net.blogjava.mobile;

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

public class Main extends Activity implements OnClickListener
{
    private String[] provinces = new String[]
    { "辽宁省", "山东省", "河北省", "福建省", "广东省", "黑龙江省" };
    private ButtonOnClick buttonOnClick = new ButtonOnClick(1);
    private ListView lv = null;
    private void showListDialog()
    {
        new AlertDialog.Builder(this).setTitle("选择省份").setItems(provinces,
                new DialogInterface.OnClickListener()
                {
                    public void onClick(DialogInterface dialog, int which)
                    {
                        final AlertDialog ad = new AlertDialog.Builder(
                                Main.this).setMessage(
                                "您已经选择了: " + which + ":" + provinces[which])
                                .show();
                        android.os.Handler hander = new android.os.Handler();
                        hander.postDelayed(new Runnable()
                        {
                            @Override
                            public void run()
                            {
                                ad.dismiss();

                            }
                        }, 5 * 1000);

                    }
                }).show();
    }

    private void showSingleChoiceDialog()
    {

        new AlertDialog.Builder(this).setTitle("选择省份").setSingleChoiceItems(
                provinces, 1, buttonOnClick).setPositiveButton("确定",
                buttonOnClick).setNegativeButton("取消", buttonOnClick).show();
        
    }


    private void showMultiChoiceDialog()
    {

        AlertDialog ad = new AlertDialog.Builder(this)
                .setIcon(R.drawable.image).setTitle("选择省份")
                .setMultiChoiceItems(provinces, new boolean[]
                { false, true, false, true, false, false },
                        new DialogInterface.OnMultiChoiceClickListener()
                        {
                            public void onClick(DialogInterface dialog,
                                    int whichButton, boolean isChecked)
                            {

                            }
                        }).setPositiveButton("确定",
                        new DialogInterface.OnClickListener()
                        {
                            public void onClick(DialogInterface dialog,
                                    int whichButton)
                            {
                                int count = lv.getCount();
                                String s = "您选择了:";
                                for (int i = 0; i < provinces.length; i++)
                                {

                                    if (lv.getCheckedItemPositions().get(i))
                                        s += i + ":"
                                                + lv.getAdapter().getItem(i)
                                                + "  ";

                                }
                                if (lv.getCheckedItemPositions().size() > 0)
                                {
                                    new AlertDialog.Builder(Main.this)
                                            .setMessage(s).show();
                                }
                                else
                                {
                                    new AlertDialog.Builder(Main.this)
                                            .setMessage("您未选择任何省份").show();

                                }

                            }
                        }).setNegativeButton("取消", null).create();
        lv = ad.getListView();
        ad.show();

    }

    private class ButtonOnClick implements DialogInterface.OnClickListener
    {
        private int index;

        public ButtonOnClick(int index)
        {
            this.index = index;
        }

        @Override
        public void onClick(DialogInterface dialog, int whichButton)
        {
            if (whichButton >= 0)
            {
                index = whichButton;
                // dialog.cancel();                 
            }
            else
            {
                if (whichButton == DialogInterface.BUTTON_POSITIVE)
                {
                    new AlertDialog.Builder(Main.this).setMessage(
                            "您已经选择了： " + index + ":" + provinces[index]).show();
                }
                else if (whichButton == DialogInterface.BUTTON_NEGATIVE)
                {
                    new AlertDialog.Builder(Main.this).setMessage("您什么都未选择.")
                            .show();

                }
            }

        }

    }

    @Override
    public void onClick(View view)
    {
        switch (view.getId())
        {
            case R.id.btnListDialog:
            {
                showListDialog();
                break;
            }
            case R.id.btnSingleChoiceDialog:
            {
                showSingleChoiceDialog();
                break;
            }
            case R.id.btnMultiChoiceDialog:
            {
                showMultiChoiceDialog();
                break;
            }
        }
    }

    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        Button btnListDialog = (Button) findViewById(R.id.btnListDialog);
        Button btnSingleChoiceDialog = (Button) findViewById(R.id.btnSingleChoiceDialog);
        Button btnMultiChoiceDialog = (Button) findViewById(R.id.btnMultiChoiceDialog);
        btnListDialog.setOnClickListener(this);
        btnSingleChoiceDialog.setOnClickListener(this);
        btnMultiChoiceDialog.setOnClickListener(this);
    }
}