将变量从活动传递到 Java 类

Question

我想将一个 int 从 FirstActivity 传递给 TheAdapter（不是一个活动）。当在 FirstActivity 中单击一个按钮时，它会打开 SecondActivity，它会创建一个 TheAdapter 的实例，并在列表视图中显示其内容。

第一个活动：

viewBtn.setOnClickListener(new View.OnClickListener(){
        @Override
        public void onClick(View v) {
            number = 5; //this is an integer
            Intent in = new Intent(FirstActivity.this, SecondActivity.class);
            startActivity(in);
        }
    });

第二个活动：

TheAdapter adapter = new TheAdapter(this, 0);
myListView.setAdapter(adapter);

我想从 FirstActivity 获取整数，以便在 TheAdapter 中使用它。

Answer 1

第一个活动：

viewBtn.setOnClickListener(new View.OnClickListener(){
    @Override
    public void onClick(View v) {
        number = 5; //this is an integer
        Intent in = new Intent(FirstActivity.this, SecondActivity.class);
        in.putExtra("name of your value (eg. adapter_int)", number);
        startActivity(in);
    }
});

第二个活动：

Intent intent = getIntent();
int yourInt = intent.getExtra("name of your value (eg. adapter_int)", 0); // 0 is a default value

Answer 2

Intent in = new Intent(FirstActivity.this, SecondActivity.class);
in.putExtra(Key , value);
startActivity(in);

//在SecondActivity中

Bundle bundle = this.getIntent().getExtras();

//for example int param
int param = 0;
if(bundle == null){
     Log.e(TAG, "bundle is null.");
}else{
     param = bundle.getInt(key);
}

如果你想要传递对象（可序列化对象）它应该很有用

public class Serializer {

public static byte[] serialize(Object obj) throws IOException {
    try(ByteArrayOutputStream b = new ByteArrayOutputStream()){
        try(ObjectOutputStream o = new ObjectOutputStream(b)){
            o.writeObject(obj);
        }
        return b.toByteArray();
    }
}

public static Object deserialize(byte[] bytes) throws IOException, ClassNotFoundException {
    try(ByteArrayInputStream b = new ByteArrayInputStream(bytes)){
        try(ObjectInputStream o = new ObjectInputStream(b)){
            return o.readObject();
        }
    }
}

}