1.启动一个activity并从它中拿到回执的值

通过startActivityForResult启动activity，从onActivityResult拿到返回值

代码示例

public class FirstActivity extends AppCompatActivity {
    private static final int REQUESTCODE = 1;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_first);
        findViewById(R.id.startIntent).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(FirstActivity.this, SecondActivity.class);
                startActivityForResult(intent, REQUESTCODE);
            }
        });
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        switch (requestCode) {
            case REQUESTCODE:
                if (resultCode == RESULT_OK) {
                    String returnData = data.getStringExtra("RETURN_DATA");
                    Toast.makeText(this, "return data: " + returnData, Toast.LENGTH_SHORT).show();
                }
                break;
            default:
                break;

        }
    }
}

通过setResult向上一个活动返回数据

public class SecondActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_second);
        findViewById(R.id.text).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent();
                intent.putExtra("RETURN_DATA", "返回数据给第一页");
                setResult(RESULT_OK, intent);
                finish();
            }
        });
    }
}

2.活动被回收了的处理

代码示例

public class FirstActivity extends AppCompatActivity {

    private String tempData = "";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_first);
        tempData = "内存回收之前需要保存的测试数据";
        if (savedInstanceState != null) {
            tempData = savedInstanceState.getString("tempdata");
        }
    }

    @Override
    protected void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        outState.putString("tempdata", tempData);
    }
}

3.启动模式

在清单文件中添加 android:launchMode

• standard
• singleTop
• singleTask
• singleInstance

standard

系统不在乎是否已经在返回栈总存在，每次启动都会重新创建一个实例

singleTop

启动活动时，如果返回栈顶已经是该活动，则不在重新创建新的活动。如果不在栈顶，则仍然会再次创建该活动。

singleTask

系统会在返回栈中检查是否存在该活动，如果存在，则直接使用它，并把这个活动之上的其他活动统统出栈。如不存在，则重新创建。

singleInstance

启用一个新的返回栈来管理这个活动。如果有上个活动A(standard)->B(singleInstance)->C(standard)依次点击跳转完，点击back键回退时，回退顺序为C->A->B。因为AC为同一个栈，C出栈后自然会显示A，A出栈后才会显示另一个栈B。

4.BaseActivity，ActivityCollector管理启动的activity

代码示例

public class ActivityCollector {
    private static List<Activity> activities = new ArrayList<>();

    public static void addActivity(Activity activity) {
        activities.add(activity);
    }

    public static void removeActivity(Activity activity) {
        activities.remove(activity);
    }

    /**
     * 退出程序
     */
    public static void finishAll() {
        for (Activity activity : activities) {
            if (!activity.isFinishing()) {
                activity.finish();
            }
        }
    }

    /**
     * 保证程序完全退出，杀掉进程,只能用于杀掉当前程序进程
     */
    public static void killProcess (){
        android.os.Process.killProcess( android.os.Process.myPid());

    }
}

public class BaseActivity extends AppCompatActivity {
    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        //打印当前活动的名称
        Log.d("BaseActivity", "Current Activity Name:  " + getClass().getSimpleName());
        ActivityCollector.addActivity(this);
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        ActivityCollector.removeActivity(this);
    }
}

5.启动activity较优方式

代码示例

public class SecondActivity extends AppCompatActivity {

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

    public static void startSecondActivity(Context context, String param1, String param2) {
        Intent intent = new Intent(context, SecondActivity.class);
        intent.putExtra("param1", param1);
        intent.putExtra("param2", param2);
        context.startActivity(intent);
    }
}