Coding Note: [Android]初學使用Inten在Activity傳值(一)

Main畫面:

點下widget1按鈕，會將 "from Main" 帶到 Second畫面

Second畫面 :

點上一頁按鈕，會回傳 "from widget1"到Main
如果不是點上一頁按鈕兒是透過其他方法回到前一頁，在Main會顯示 "無參數"

startActivityForResult()除了傳值之外，還會回傳一個requestCode
所以Main要加入onActivityResult()方法,來接收辨別是哪個Activity回傳的requestCode

參數一定是從A-->B , B-->A AB兩個Activity在溝通
傳回參數的時候，只會接收參數，畫面不會刷新成預設畫面

最後要記得在AndroidManifest.xml 註冊 Activity

<activity android:name=".SecondActivityName"></activity>

	public class MainActivity extends AppCompatActivity {
	private Button widget1;
	private int REQUEST_CODE;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
	super.onCreate(savedInstanceState);
	setContentView(R.layout.activity_main);

	widget1 =(Button)findViewById(R.id.btnNext);

	//下一頁
	widget1.setOnClickListener(new Button.OnClickListener() {
	public void onClick(View v) {
	Intent intent1 = new Intent();
	intent1.setClass(MainActivity.this, widgetActivity.class);
	intent1.putExtra("activityMain", "from Main");
	//當 REQUEST_CODE =-1 等於執行 startActivity
	// widgetActivity 回傳資料要使用 setResult
	startActivityForResult(intent1,REQUEST_CODE);

	//startActivity(intent1);
	//MainActivity.this.finish();
	}
	});

	}

	//接收回傳值的 Function
	@Override
	protected void onActivityResult(int requestCode , int resultCode,Intent data)
	{
	if(requestCode == REQUEST_CODE)
	{
	if (resultCode == RESULT_OK){
	String temp=null;
	Bundle extras = data.getExtras();
	if(extras != null)
	{
	temp = extras.getString("widget");
	}
	setTitle(temp);
	}else
	{
	setTitle("無參數");
	}
	}
	}
	}

view raw MainActivity.java hosted with ❤ by GitHub

	public class widgetActivity extends AppCompatActivity {
	private Button prev;
	private String data;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
	super.onCreate(savedInstanceState);
	setContentView(R.layout.widget);
	prev=(Button)findViewById(R.id.btnPrev);

	Bundle extras =getIntent().getExtras();
	if(extras !=null)
	{
	data=extras.getString("activityMain");
	setTitle("widget :" + data);
	}else
	{
	setTitle("widget");
	}

	prev.setOnClickListener(new Button.OnClickListener(){
	public void onClick(View v)
	{
	Intent intent =new Intent();
	intent.setClass(widgetActivity.this,MainActivity.class);
	// Bundle 傳遞 Data
	Bundle bundle = new Bundle();
	bundle.putString("widget","from widget1");
	intent.putExtras(bundle);
	setResult(RESULT_OK, intent);
	finish();
	}
	});
	}