Android应用程序四大组件之Activity(二)

Activity状态保存

1.onSaveInstanceState()/onCreate()/onRestoreInstanceState()

系统在回收当期Activity之前会调用onSaveInstanceState(),Back&Home两个键不会调用此方法.例如电子书程序,阅读到某一页内存不足被系统回收.可以通过此方法记录第几页.在程序重新启动时,在onCreate()里判断重新读取退出时第几页状态.它的参数Bundle是key-value形式

	private final String SAVE_INSTANCE_TAG = "MainTestActivity.Saveinstancetag";
	EditText editText = null;
	
	@Override
    protected void onSaveInstanceState(Bundle outState) {
		
		if(outState!=null){
			outState.putString(this.SAVE_INSTANCE_TAG, "hello!!!!");
		}
		System.out.println("onSaveInstanceState");
    	
    	super.onSaveInstanceState(outState);
    }

   /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        
        System.out.println("onCreate");
        editText = (EditText)findViewById(R.id.myEditText);
        
        if(editText!=null&&savedInstanceState!=null){
        	editText.setText(savedInstanceState.getString(SAVE_INSTANCE_TAG));
        }
        if(savedInstanceState!=null){
        	System.out.println("savedInstanceState"+savedInstanceState);
        }
    }

onRestoreInstanceState()不一定是与onSaveInstanceState()成对使用的.调用此方法时.Activity定是被系统Destroy掉的.其Bundle参数值也可以传到onCreate()

   @Override
    protected void onRestoreInstanceState(Bundle savedInstanceState) {
    	// TODO Auto-generated method stub
    	String tag= savedInstanceState.getString(this.SAVE_INSTANCE_TAG);
    	super.onRestoreInstanceState(savedInstanceState);
    }

2.借助Activity Lifecycle+Preference

使用这种方式状态保存可以是.横竖屏幕切换,按Home or Back键之后再回来.

	@Override
	protected void onPause() {
		// TODO Auto-generated method stub
		super.onPause();
		// 写入 SharedPreferences
		SharedPreferences preferences = getSharedPreferences("name",
				MODE_PRIVATE);
		Editor editor = preferences.edit();
		editor.putBoolean("boolean_key", true);
		editor.putString("string_key", "string_value");
		editor.commit();

	}

	@Override
	protected void onResume() {
		// TODO Auto-generated method stub
		super.onResume();
		// 读取 SharedPreferences
		SharedPreferences preferences = getSharedPreferences("name",
				MODE_PRIVATE);
		preferences.getBoolean("boolean_key", false);
		preferences.getString("string_key", "default_value");
	}

Activity之间通信

1.无参数Activity跳转

Intent intent = new Intent(Activity1.this, Activity2.class);
startActivity(intent); 

2.向下一个Activity传递数据（使用Bundle和Intent.putExtras）

Intent intent = new Intent();
intent.setClass(Ex03_10Activity.this, Ex03_10_1.class);
				
Bundle bundle = new Bundle();
bundle.putDouble("height", height);
bundle.putString("sex", sex);
intent.putExtras(bundle);
				
startActivity(intent); //startActivityForResult(intent, 0);

//数据的接收
 Bundle bundle = this.getIntent().getExtras();
 
 String sex = bundle.getString("sex");
 double height = bundle.getDouble("height");

3.向上一个Activity返回结果（使用setResult，针对startActivityForResult(it,REQUEST_CODE)启动的Activity）

Intent intent=getIntent();
 Bundle bundle2=new Bundle();
 bundle2.putString("sex", "Man!");
 intent.putExtras(bundle2);
 setResult(RESULT_OK, intent);

4.回调上一个Activity的结果处理函数（onActivityResult）

	@Override
	protected void onActivityResult(int requestCode, int resultCode, Intent data) {
		// TODO Auto-generated method stub
		switch (requestCode) {
		case RESULT_OK:
			Bundle bundle = data.getExtras();
			String sex = bundle.getString("sex");
			double height = bundle.getDouble("height");
			et.setText(""+height);
			if(sex.equals("M")){
				rb1.setChecked(true);
			}else{
				rb2.setChecked(true);
			}
			break;

		default:
			break;
		}
	}

打电话
1. //叫出拨号程序
2. Uri uri = Uri.parse("tel:[phone]");
3. Intent it = new Intent(Intent.ACTION_DIAL, uri);
4. startActivity(it);
1. //直接打电话出去
2. Uri uri = Uri.parse("tel:[phone]");
3. Intent it = new Intent(Intent.ACTION_CALL, uri);
4. startActivity(it);
5. //用這個，要在 AndroidManifest.xml 中，加上
6. //<uses-permission id="android.permission.CALL_PHONE" />

传送SMS/MMS
1. //调用短信程序
2. Intent it = new Intent(Intent.ACTION_VIEW, uri);
3. it.putExtra("sms_body", "The SMS text");
4. it.setType("vnd.android-dir/mms-sms");
5. startActivity(it);
1. //传送消息
2. Uri uri = Uri.parse("smsto://0800000123");
3. Intent it = new Intent(Intent.ACTION_SENDTO, uri);
4. it.putExtra("sms_body", "The SMS text");
5. startActivity(it);
1. //传送 MMS
2. Uri uri = Uri.parse("content://media/external/images/media/23");
3. Intent it = new Intent(Intent.ACTION_SEND);
4. it.putExtra("sms_body", "some text");
5. it.putExtra(Intent.EXTRA_STREAM, uri);
6. it.setType("image/png");
7. startActivity(it);

以上应用实例更多请参考原作者http://www.cnblogs.com/feisky/archive/2010/01/16/1649081.html