putextra和getextra不将字符串传递给下一个活动

Question

我有三个活动A，B和C

在我的B活动中，我有一个imageview，当我从活动A到B获得一个String时，该imageview应该可见。

当我从活动C到B获得字符串时，imageview应该不可见。

//From activity A
Intent iin= getIntent();
Bundle b = iin.getExtras();
//From Activity C
Intent i2=getIntent();
Bundle abcd=i2.getExtras();

if(b!=null)
{
    String j =(String) b.get("arrowvisi");

    Toast.makeText(getApplicationContext(), j, Toast.LENGTH_LONG).show();
    if(j==b.get("arrowvisi"))
    {
        img_back.setVisibility(View.VISIBLE);
        Toast.makeText(getApplicationContext(), "Operational arrow visible", Toast.LENGTH_LONG).show();

    }
    else
    {
        if(abcd!=null)
        {
            String jst =(String) abcd.get("arrow_val");
            if(jst==abcd.get("arrow_val"))
            {
                img_back.setVisibility(View.GONE);
                Toast.makeText(getApplicationContext(), "scan dispatch visble", Toast.LENGTH_LONG).show();
            }
            else
            {
                //img_back.setVisibility(View.GONE);

                System.out.println("from scan dispatch");
                Toast.makeText(getApplicationContext(), "scan dispatch not visible", Toast.LENGTH_LONG).show();
            }

        }


        Toast.makeText(getApplicationContext(), "Operational not visible", Toast.LENGTH_LONG).show();
    }

}

Answer 1

首先，要比较java中的字符串，需要使用.equals

所以改变

 if(j==b.get("arrowvisi"))

至

 if(j.equals(b.getString("arrowvisi")))

和

if(jst==abcd.get("arrow_val"))

至

if(jst.equals(abcd.getString("arrow_val")))

其次，您的条件将永远为真，因为您总是在比较两个相等的值，即首先在jst获取值，然后再比较相同的值。

编辑：解决空指针更改

 String j =(String) b.get("arrowvisi");

至

 String j = b.getString("arrowvisi");

和

 String jst =(String) abcd.get("arrow_val");

至

 String jst =abcd.getString("arrow_val");

并发布logcat异常。

Answer 2

更换

String j = (String) b.get("arrowvisi");

与

String j = b.getString("arrowvisi");

和

String jst = (String) abcd.get("arrow_val");

与

String jst = abcd.getString("arrow_val");

还字符串比较应该像

j.equals(b.getString("arrowvisi")) // change again

和

jst.equals(abcd.getString("arrow_val"))  // change again 

因此，最终的答案应该类似于

//From activity A
Intent iin = getIntent();
Bundle b = iin.getExtras();

//From Activity C
Intent i2 = getIntent();
Bundle abcd = i2.getExtras();

if(b != null){
    String j = "String to check"; // Replace content inside "" with your string 
    Toast.makeText(getApplicationContext(), j, Toast.LENGTH_LONG).show();
    if(j.equals(b.getString("arrowvisi"))){
        img_back.setVisibility(View.VISIBLE);
        Toast.makeText(getApplicationContext(), "Operational arrow visible", Toast.LENGTH_LONG).show();
    }else{
        if(abcd != null){
            String jst = "String to check"; // Replace with string you want to check
            if(jst.equals(abcd.getString("arrow_val"))){
                img_back.setVisibility(View.GONE);
                    Toast.makeText(getApplicationContext(), "scan dispatch visble", Toast.LENGTH_LONG).show();
                }else{
                    //img_back.setVisibility(View.GONE);
                    System.out.println("from scan dispatch");
                    Toast.makeText(getApplicationContext(), "scan dispatch not visible", Toast.LENGTH_LONG).show();
                }
            }
            Toast.makeText(getApplicationContext(), "Operational not visible", Toast.LENGTH_LONG).show();
        }
    }

还要注意 ，做类似的事情

String jst = abcd.getString("arrow_val"));
if(jst.equals(abcd.getString("arrow_val"))) // this will be always true

这将导致if语句始终为true。

2种选择：

1）删除if语句，因为它始终为true。

2）更改String jst = "Some string to compare" （对此jst = "Some string to compare"更改），现在在if循环中使用jst.equals(abcd.getString("arrow_val"))比较jst与getString("arrow_val")

Answer 3

改变这个

String j = (String) b.get("arrowvisi");

与

String j = b.getString("arrowvisi");

和

String jst = (String) abcd.get("arrow_val");

与

String jst = abcd.getString("arrow_val");

也把它放在括号中

b.get("arrowvisi")
abcd.get("arrow_val")