Question

我正在与改造工作以获取一些统计信息。他们到达应用程序。当我尝试将某些TextView的文本设置为值时，它们会抛出NullPointerException。有什么我应该知道的吗？

public void init() {
    getStatistics();
txtNrCompleted.setText(String.format("%s", statistics.getTask()));
}

private void getStatistics(){
    endpoints = RetrofitJsonCaller.call(APIEndpoints.class);
    callStatistics = endpoints.getStatistics(URLEndpoints.getStatistics());
    callStatistics.enqueue(new Callback<STATISTIC>() {
        @Override
        public void onResponse(Call<STATISTIC> call, Response<STATISTIC> response) {
            if(response.isSuccessful()) {
                setStatistics(response.body());

            }else{
                Log.d("STATISTICS", "Error: " + response.code());
            }
        }

        @Override
        public void onFailure(Call<STATISTIC> call, Throwable t) {
            Timber.d(t.getMessage());
        }
    });

}

public void setStatistics(STATISTIC statistics){
    this.statistics = statistics;
}

日志：

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Integer com.example.taskmanagement.model.STATISTIC.getTaskComplet()' on a null object reference
    at com.example.taskmanagement.MainActivity.onCreate(MainActivity.java:111)
    at android.app.Activity.performCreate(Activity.java:6948)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1126)

Answer 1

Retrofit正在发出异步获取统计信息的调用，但是您正在同步设置TextView中的文本。您调用getStatistics()会触发调用以获取新的统计信息，但不等待其完成。然后，您立即设置文本，此时statistics对象仍为null。得到成功的响应后，您需要更新TextView。例如：

public void init() {
    getStatistics(); 
}

private void getStatistics() {
    ...
        @Override
        public void onResponse(Call<STATISTIC> call, Response<STATISTIC> response) {
            if (response.isSuccessful()) {
                setStatistics(response.body()); 
                // Call the code to update your UI here, as we have now received the stats
                updateUI(); 
            } else {
                ...
            }
        }
    ...
}

...

private void updateUI() {
    textNrCompleted.setText(String.format("%s", statistics.getTask())); 
}

改造后设置文本

1 个答案: