Question

我有两个活动，第一个活动有一个名为songurl的公共String var，按钮导致了第二个活动，第二个活动有mediaplayer从第一个活动中的String var接收URL，然后开始播放，但问题是mediaplayer没有不起作用，我遇到了错误

这里是MainActivity1.kt或.java作为您的语言：-

class Magazine {
  constructor() {
    this.hamburgers = [];
  }

  sumHamburgers() {
    return this.hamburgers.map(el => el.price).reduce((p, c) => p + c);
  }

  hamburgersAvgN() {
    return this.sumHamburgers() / Hamburger.counter;
  }

  toStorage() {
    let serialCounter = JSON.stringify(Hamburger.counter);
    let serialAvgN = JSON.stringify(this.hamburgersAvgN());
    return localStorage.setItem(['orders', 'avg'], [`number of orders: ${serialCounter}`, ` average check: ${serialAvgN} UAH`]);
  }
}

class Hamburger {
  constructor(size, ...stuffing) {
    this.size = size;
    this.stuffing = stuffing;
    this.toppingArr = [];
    this.counter = ++Hamburger.counter;
  }

  calculatePrice() {
    const stuffingCost = this.stuffing.map(el => el.price).reduce((p, c) => p + c);
    let allCost;
    if (this.toppingArr.length === 0) {
      return allCost = this.size.price + stuffingCost;
    } else {
      const toppingCost = this.toppingArr.map(el => el.price).reduce((p, c) => p + c);
      return allCost = this.size.price + stuffingCost + toppingCost;
    }
  }
}

Hamburger.counter = 0;

Hamburger.small = {
  name: 'small',
  price: 10,
  kcal: 200
}

Hamburger.cheese = {
  name: 'cheese',
  price: 4,
  kcal: 10
}

Hamburger.meet = {
  name: ' meet',
  price: 40,
  kcal: 103
}

let magazine = new Magazine;
magazine.hamburgers.push(new Hamburger(Hamburger.small, Hamburger.meet));
magazine.hamburgers.push(new Hamburger(Hamburger.small, Hamburger.cheese));
magazine.hamburgers.push(new Hamburger(Hamburger.small, Hamburger.meet));

console.log(magazine.sumHamburgers());

这是 MainActivity2：-

  lateinit var songurl :String
class MainActivity1 : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
    songurl = "https//...... My URL"

        var btnstart_MainActivity2:Button = findViewById(R.id.btn)
        btnstart_MainActivity2.setOnClickListener {
            startActivity(Intent(this,Main2Activity::class.java))
        }

    }
}

这是错误
class Main2Activity : AppCompatActivity() { lateinit var mediaplayer: MediaPlayer override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) mediaplayer= MediaPlayer() mediaplayer.setDataSource(songurl) mediaplayer.prepare() mediaplayer.start() } }

Answer 1

您的问题是您的songurl仅在您的第一次活动中出现。活动2中没有任何价值甚至分配。

考虑将其作为意图的bundle参数传递：

Activity1:
Bundle bundle= new Bundle();
bundle.putString("key", songurl);

Intent i = new Intent(Activity1.this,Activity2.class);
i.putExtras(bundle);
startActivity(i);

Activity2:
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_another_activity);

    Bundle p = getIntent().getExtras();
    String songurl = p.getString("key");

}

示例在Java中。

Answer 2

您应该在Android Intent Extras中发送songUrl。出现错误的原因是，它未在您在活动1中定义的活动2中定义。

发送更多意向

var intent = Intent(this,Main2Activity::class.java)
intent.putExtra("songurl", songurl)

获得更多其他活动

if(getIntent().hasExtra("songurl"){
 var songurl = getIntent().getStringExtra("songurl")
}

尽管我做了lateinit属性songurl尚未初始化

2 个答案: