03 Activity之间传递参数

一、传递简单数据

发送数据：

Intent intent = new Intent(MainActivity.this, OtherActivity.class);
intent.putExtra("data", "data value");
startActivity(intent);

接受数据：

String data = getIntent().getStringExtra("data");
textView.setText(data);

优化代码：

// 传递参数
public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }

    public void sendArgs(View view) {
        Intent intent = OtherActivity.newIntent(this, "data value");
        startActivity(intent);
    }
}

// 接受参数
public class OtherActivity extends AppCompatActivity {

    private static final String ARG = "data";

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

        TextView textView = (TextView) findViewById(R.id.tv);
        String data = getIntent().getStringExtra(ARG);
        textView.setText(data);
    }

    // 解除参数名称"data"带来的依赖性
    public static Intent newIntent(Context context, String data) {
        Intent intent = new Intent(context, OtherActivity.class);
        intent.putExtra(ARG, data);
        return intent;
    }
}

二、传递数据包Bundle

发送数据包：

Intent intent = new Intent(MainActivity.this, OtherActivity.class);
Bundle bundle = new Bundle();
bundle.putString("name", "xian xiaotao");
bundle.putInt("age", 28);
intent.putExtras(bundle);
startActivity(intent);

接受数据包：

Bundle data = getIntent().getExtras();
textView.setText(String.format(Locale.getDefault(), "name=%s,age=%d", data.getString("name"), data.getInt("age")));

三、传递值对象

实现Parcelable

import android.os.Parcel;
import android.os.Parcelable;

public class User implements Parcelable {
    private String mName;
    private int mAge;

    public User(String name, int age) {
        mName = name;
        mAge = age;
    }

    public String getName() {
        return mName;
    }

    public void setName(String name) {
        mName = name;
    }

    public int getAge() {
        return mAge;
    }

    public void setAge(int age) {
        mAge = age;
    }

    @Override
    public int describeContents() {
        return 0;
    }

    @Override
    public void writeToParcel(Parcel dest, int flags) {
        // 更复杂的数据借用Bundle
        dest.writeString(getName());
        dest.writeInt(getAge());
    }

    public static final Creator<User> CREATOR = new Creator<User>() {
        @Override
        public User createFromParcel(Parcel source) {
            return new User(source.readString(), source.readInt());
        }

        @Override
        public User[] newArray(int size) {
            return new User[size];
        }
    };
}

传递参数：

Intent intent = new Intent(MainActivity.this, OtherActivity.class);
intent.putExtra("user", new User("xian xiaotao", 28));
startActivity(intent);

接收参数

User user = getIntent().getParcelableExtra("user");
textView.setText(String.format(Locale.getDefault(), "name=%s,age=%d", user.getName(), user.getAge()));

Serializable的作用是为了保存对象的属性到本地文件、数据库、网络流、rmi以方便数据传输，当然这种传输可以是程序内的也可以是两个程序间的。而Android的Parcelable的设计初衷是因为Serializable效率过慢，为了在程序内不同组件间以及不同Android程序间(AIDL)高效的传输数据而设计，这些数据仅在内存中存在，Parcelable是通过IBinder通信的消息的载体。
Parcelable的性能比Serializable好，在内存开销方面较小，所以在内存间数据传输时推荐使用Parcelable，如activity间传输数据，而Serializable可将数据持久化方便保存，所以在需要保存或网络传输数据时选择Serializable，因为android不同版本Parcelable可能不同，所以不推荐使用Parcelable进行数据持久化

四、获取Activity返回参数

public class QuizActivity extends AppCompatActivity {

	private static final int REQUEST_CODE_CHEAT = 0;

	... 

	// startActivityForResult代码
	Intent i = CheatActivity.newIntent(QuizActivity.this, answerIsTrue);
    startActivityForResult(i, REQUEST_CODE_CHEAT);

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        if (resultCode != Activity.RESULT_OK)
            return;

        if (requestCode == REQUEST_CODE_CHEAT) {
            if (data == null)
                return;
            mIsCheater = CheatActivity.wasAnswerShown(data);
        }
    }
}

public class CheatActivity extends AppCompatActivity {
	private static final String EXTRA_ANSWER_SHOWN = "com.xxtking.geoquiz.CheatActivity.answer_shown";

	...

	private void setAnswerShownResult(boolean isAnswerShown) {
        Intent data = new Intent();
        data.putExtra(EXTRA_ANSWER_SHOWN, isAnswerShown);
        setResult(RESULT_OK, data);
    }

	public static boolean wasAnswerShown(Intent result) {
        return result.getBooleanExtra(EXTRA_ANSWER_SHOWN, false);
    }
}