Android中数据的传递

Posted 2020-08-15 醉清风

android中当两个Activity需要有信息交互的时候，可以使用Intent。具体来说：

发送单一类型数据：

发送方：
String data = "Hello SecondActivity";
Intent intent = new Intent(FirstActivity.this, SecondActivity.class);
intent.putExtra("extra_data", data);
startActivity(intent); #在onClick中调用
接收方：
Intent  intent = getIntent();
String data = intent.getStringExtra("extra_data");#可以在onCreate中读取

除了putExtra("key", value)/getStringExtra("key")之外, 根据传递的value的类型还有很多对，比如：

putExtra("key", intvalue)/getintExtra("key")
putExtra("key", floatvalue)/getfloatExtra("key")
putExtra("key", doublevalue)/getDoubleExtra("key")
putExtra("key", bundlevalue)/getBundleExtra("key")

...

发送多种数据类型的组合：

也可以用Bundle把很多数据类型（包括嵌套Bundle）放到Bundle中一并发送：

//sender
Bundle b = new Bundle();
b.putInt("age", 2);
b.putString("data", "hello");
intent.putExtras(b);
startActivity(intent);

//receiver
Intent i = getIntent();
Bundle b = i.getExtras();
int age = b.getInt("age");
String data = b.getString("data");

发送类对象：

方法1：Serializable

Serializable是Java提供的序列化方法，优点是使用简单，一切由系统负责；缺点是速度稍慢。

public class User implements Serializable{
    private String name;
    private Integer age;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public User(String name, Integer age){
        this.name = name;
        this.age = age;
    }
}

//sender
intent.putExtra("user", (Serializable) new User("JM", 30));

//Receiver
Intent i = getIntent();
User user = (User) i.getSerializableExtra("user");
textView.setText(String.format("name: %s, age: %s", user.getName(), user.getAge()));

方法2：Parcelable

public class User implements Parcelable{
    private String name;
    private Integer age;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public User(String name, Integer age){
        this.name = name;
        this.age = age;
    }

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

    @Override
    public void writeToParcel(Parcel parcel, int i) {
        //write all the fields that want to send
        parcel.writeString(getName());
        parcel.writeInt(getAge());
    }

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

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

//Sender
            intent.putExtra("user", (Parcelable) new User("JM", 30));
                startActivity(intent);

//Receiver
        User user = (User) i.getParcelableExtra("user");
        textView.setText(String.format("name: %s, age: %s", user.getName(), user.getAge()));

如果在User中有多个同类型字段，比如String，可以用Bundle来实现：

@Override
    public void writeToParcel(Parcel parcel, int i) {
        //write all the fields that want to send
//        parcel.writeString(getName());
//        parcel.writeInt(getAge());
        Bundle b = new Bundle();
        b.putString("name", getName());
        b.putInt("age", getAge());
        parcel.writeBundle(b);
    }

    public static final Creator<User> CREATOR = new Creator<User>() {
        @Override
        public User createFromParcel(Parcel parcel) {
//            return new User(parcel.readString(), parcel.readInt());
            Bundle b = parcel.readBundle();
            return new User(b.getString("name"), b.getInt("age"));
        }

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

从别的Activity得到返回结果：

启动端：

startActivityForResult(intent, 0);

0表示请求码，说明此次请求的意图是什么。

接收端：

        Intent i = new Intent();
        i.putExtra("data", editText.getText().toString());
        setResult(RESULT_OK, i);
        finish();