如何使用startActivity與startActivityForResult

情境

如果想要讓一個Activity跳到另外一個Activity的話, 就可以使用Intent,
設定好要轉跳的Activity, 然後利用startActivity或者startActivityForResult來執行。

程式碼說明

先寫原始的頁面,

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    >
    <TextView
        android:layout_width="match_parent"
        android:layout_height="30dp"
        android:gravity="center_vertical"
        android:layout_marginLeft="10dp"
        android:hint="hello"
        android:id="@+id/result_text"
        />
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="startActivityForResult"
        android:id="@+id/start_activity_for_result"
        />
</LinearLayout>

一個TextView用來呈現回來的字串
Button會轉跳到另外一隻Activity

然後再寫一個另外一個Activity的頁面。

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
    <EditText
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:id="@+id/other_activtity_edittext"
        />
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="startActivityForResult back"
        android:id="@+id/start_activity_for_result_back"
        />
</LinearLayout>

這邊有一個輸入框可以讓你輸入要回傳的文字

public class MainActivity extends AppCompatActivity {
    private Button startActivtyForResult;
    private TextView resultText;
    public static final int resultNum = 0;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        init();
    }
    private void init(){
        startActivtyForResult = (Button) findViewById(R.id.start_activity_for_result);
        resultText = (TextView) findViewById(R.id.result_text);
        startActivtyForResult.setOnClickListener(new View.OnClickListener(){
            @Override
            public void onClick(View v) {
                Intent intent = new Intent();
                intent.setClass(MainActivity.this, OtherActivity.class);
                startActivityForResult(intent, resultNum);
            }
        });
    }
}

當Button按下去就會轉跳到下一個Activity

定義第二個方法, 當按下去的時候,
第二個按鈕會利用startActivityForActivity轉跳到另外一個Activity。

public class OtherActivity extends AppCompatActivity {
    private EditText otherActivityEditText;
    private Button startActivityForResultBack;
    public static final String FLAG = "BACK_STRING";
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_other);
        otherActivityEditText = (EditText) findViewById(R.id.other_activtity_edittext);
        startActivityForResultBack = (Button)    findViewById(R.id.start_activity_for_result_back);

        startActivityForResultBack.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent();
                Bundle b = new Bundle();
                b.putString(FLAG, otherActivityEditText.getText().toString());
                intent.putExtras(b);
                OtherActivity.this.setResult(RESULT_OK, intent);
                finish();
            }
        });
    }
}

當另外一個Activity傳送回來的時候, 它會接收由startActivityForResult傳送回來的資訊。

@Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        if(resultCode == RESULT_OK){
            if(requestCode == resultNum){
                resultText.setText(data.getExtras().getString(OtherActivity.FLAG));
            }
        }
    }

當使用startActivityForResult的時候, A Activity狀態長這樣

onCreat()-> onStart()-> onResume()-> 按下到下一個Activity Button 
-> onPause() -> onStop()-> 按回到A Activity Button 
-> onRestart() -> onStart() -> onResume()

程式碼